Patent Application
20190194756
The present invention relates to a gene panel of at least 14 genes or the combination of said at least 14 genes for use in a method of diagnosis of a genetic disposition to pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH). The present invention relates to using said gene panel or combination of genes in the in vitro or ex vivo diagnosis of a genetic disposition to pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH). The present invention relates to a method and a kit for the diagnosis of a genetic disposition to pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH). The present invention further relates to said gene panel, method and kit with respect to a genetic disposition to pulmonary veno-occlusive disease (PVOD) and/or hereditary haemorrhagic telangiectasia (HHT).
Pulmonary arterial hypertension (PAH) is characterised by plexiform lesions of the small pulmonary arteries leading to an increase in pulmonary vascular resistance and right heart failure (Galiè et al., 2016; Grünig et al., 2011). The recent decade witnessed the discovery of hereditary predisposition to PAH. In 2000, mutations in the bone morphogenic protein receptor type 2 (BMPR2) gene, a member of the transforming growth factor-beta (TGF-β) super family, have been identified in families with autosomal dominantly inherited PAH (hereditary PAH, HPAH) (see e.g. Deng et al., 2000; Grünig et al., 2000; Lane et al., 2000). Defects of the BMPR2 gene have been detected to be the major heritable cause for development of PAH (Machado et al., 2015; Soubrier et al., 2013) albeit having an incomplete penetrance of about 20-40% (Larkin et al., 2012; Sztrymf et al., 2007) in single families up to 50% (Newman et al., 2001; Frydman et al., 2012). In approximately 85% of familial PAH and 14-35% of sporadic idiopathic PAH (IPAH) cases, mutations of BMPR2 gene were identified (Soubrier et al., 2013; Pfarr et al., 2011; Kabata et al., 2013; Girerd et al., 2016). In PAH patients with hereditary haemorrhagic telangiectasia (HHT) mutations in the activin receptor-like kinase 1 (ALK1 or ACVRL1) (Trembath et al., 2001) and endoglin (ENG) (Chaouat et al., 2004; Harrison et al., 2003) gene were documented. Therefore, diagnostic genetic testing within the last decade has concentrated on these 3 genes and is usually performed by direct Sanger sequencing in a sequential manner, terminating the sequencing as soon as a mutation has been identified in one of these genes. However, within the last years further genes belonging to the BMPR2/Alk1-signalling pathway have been detected by whole exome next generation sequencing (NGS) to be involved in the pathogenesis of PAH and/or pulmonary veno-occlusive disease (PVOD) and/or hereditary haemorrhagic telangiectasia (HHT). HHT often lead to pulmonary arterial hypertension which drastically worsens patients' survival (Lyle et al., 2016). In hereditary PVOD cases 100% of hereditary patients carried two mutations in the gene EIF2AK4 (Girerd et al., 2016). The ERS/ESC guidelines thus suggest a mutation analysis to be preferred to a biopsy to ascertain the diagnosis of PVOD (Galiè et al., 2016).
Recently mutations and large deletions were also discovered in the three major genes BMPR2, ENG and ALK1 in patients with chronic thromboembolic pulmonary hypertension (CTEPH) (Feng et al., 2014, Xi et al., 2016). Therefore, it is likely that genetic defects also play a role in the manifestation of CTEPH.
The availability of genetic testing including genetic counselling has become more and more important for patient care and for family members of PAH patients. Therefore, genetic testing and counselling has been addressed and recommended in the new European Respiratory Society/ European Society of Cardiology (ERS/ESC)-guidelines for selected PAH patients and their family member (Galiè et al., 2016). The most common molecular approach is genetic testing by Sanger technique of only 3 genes. This might no longer be appropriate, since today at least 14 PAH/CTEPH/PVOD/HHT genes are known and the Sanger technique assessing one gene at a time is a very time consuming and expensive method (at least 11 h analysis time—in reality 1-2 weeks turnaround time for the three major genes). Furthermore, there is growing evidence that in some patients at least 2 gene defects are necessary for disease manifestation (second hit hypothesis) (Eichstaedt et al., 2016; Rodriguez Viales et al., 2015; Wang et al., 2014).
There is a need in the art for improved means and methods for diagnosing PAH/CTEPH and screening of PAH/CTEPH, including PVOD and/or HHT.
According to the present invention this object is solved by providing a gene panel or combination of genes comprising at least the genes with the nucleotide sequence of SEQ ID Nos. 1 to 14 for use in a method of diagnosis of a genetic disposition to pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH).
According to the present invention this object is solved by using a gene panel or combination of genes comprising at least the genes with the nucleotide sequence of SEQ ID Nos. 1 to 14 in the in vitro or ex vivo diagnosis of a genetic disposition to pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH).
According to the present invention this object is solved by a method for the diagnosis of genetic defects in pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH), comprising the following steps:
According to the present invention this object is solved by providing a kit for the diagnosis of genetic defects in pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH), comprising
Before the present invention is described in more detail below, it is to be understood that this invention is not limited to the particular methodology, protocols and reagents described herein as these may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. For the purpose of the present invention, all references cited herein are incorporated by reference in their entireties.
Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “1 to 96” or “2 to 96” should be interpreted to include not only the explicitly recited values of 1 to 96, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 1, 2, 3, 4, 5 . . . 91, 92, 93, 94, 95, 96 and sub-ranges such as from 2 to 10, 15 to 50, 1 to 90, etc. This same principle applies to ranges reciting only one numerical value, such as “at least 2”. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.
In this disclosure we disclose the development of a PAH/CTEPH-specific gene diagnostic panel using NGS and including 14 known PAH and further candidate genes. The new procedure is widely available, easy to perform and will allow assessing up to 50 genes and up to 96 patients at once in a short time at reduced costs. Furthermore, it is possible to assess sensitivity and specificity of this new panel in a cohort of patients/family members using additional Sanger sequencing.
Preferably, the use comprises the in vitro or ex vivo diagnosis of a genetic disposition to pulmonary veno-occlusive disease (PVOD) and/or hereditary haemorrhagic telangiectasia (HHT).
The terms “PAH/CTEPH” or “PAH/CTEPH/PVOD/HHT”, such as when referring to gene(s) and/or patient(s), are used interchangeably throughout the specification.
As discussed above, the present invention provides a gene panel or combination of genes comprising at least the genes with the nucleotide sequence of SEQ ID Nos. 1 to 14 for use in a method of diagnosis of pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH), in particular the diagnosis of a genetic predisposition to PAH and/or CTEPH.
As discussed above, the present invention provides the use of a gene panel or combination of genes comprising at least the genes with the nucleotide sequence of SEQ ID Nos. 1 to 14 in the in vitro or ex vivo diagnosis of pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH), in particular the diagnosis of a genetic predisposition to PAH and/or CTEPH.
Preferably, the present invention provides the use of the gene panel or combination of genes in the in vitro or ex vivo diagnosis of pulmonary arterial hypertension (PAH), chronic thromboembolic pulmonary hypertension (CTEPH), pulmonary veno-occlusive disease (PVOD) and/or hereditary haemorrhagic telangiectasia (HHT), in particular the diagnosis of a genetic predisposition to PAH and/or CTEPH and/or PVOD and/or HHT.
In a preferred embodiment, the gene panel or combination of genes of the present invention is used which comprises the at least 14 genes with the nucleotide sequence of SEQ ID Nos. 1 to 14 and up to the 50 genes, wherein said 50 genes comprise the genes with the nucleotide sequence of SEQ ID Nos. 1 to 43.
In a preferred embodiment, the gene panel or combination of genes comprises the at least the genes with the nucleotide sequence of SEQ ID Nos. 1 to 14 and 42.
Preferably a range of at least 14 genes and up to 50 genes are used. In one embodiment 15 genes are used, in one embodiment 36 genes are used, in one embodiment 43 genes are used.
In a preferred embodiment, the gene panel or combination of genes is used which comprises at least the genes with the nucleotide sequence of SEQ ID Nos. 1 to 14 and 42, more preferably comprises the genes with the nucleotide sequence of SEQ ID Nos. 1 to 36, more preferably comprises the genes with the nucleotide sequence of SEQ ID Nos. 1 to 43.
The term “gene panel” or “combination of genes” or “gene set” or “set of genes” refers to the genes included on the panel which are either genes identified as mutated in PAH, CTEPH, PVOD and/or HHT patients or such genes which have been associated with PH in animal models and might contribute to disease manifestation in case of a genetic defect.
The inventors have found that the following set of 14 genes allows for the diagnosis of genetic defects of PAH and partly CTEPH, PVOD and/or HHT:
Mutations in these 14 genes or “core genes” have been shown to lead to PAH manifestation and partly to CTEPH, PVOD and/or HHT manifestation.
The genes ACVRL1, BMRP2, ENG (SEQ ID NOs. 1, 3, 6) have been found to be mutated in CTEPH.
The gene EIF2AK4 (SEQ ID NO 5) has been shown to be mutated in PVOD.
The genes ACVRL1, BMPR2, ENG, GDF2, SMAD4 (SEQ ID NOs. 1, 3, 6, 7, 12) have been shown to be mutated in HHT.
The inventors have found that the following set of 15 genes further allows for the diagnosis of genetic defects of PAH and partly CTEPH, PVOD and/or HHT:
Within the last years genes belonging to the BMPR2/Alk1-signalling pathway have been detected by whole exome next generation sequencing (NGS) to be involved in the pathogenesis of PAH, pulmonary veno-occlusive disease (PVOD) and/or HHT. In hereditary PVOD cases 100% of hereditary patients carried two mutations of the gene EIF2AK4 (Girerd et al., 2016). The ERS/ESC guidelines thus suggest a mutation analysis to be preferred to a biopsy to ascertain the diagnosis of PVOD (Galiè et al., 2016). Defects in genes apart from BMPR2 leading to PAH manifestation have been described so far in 0.5-4% of PAH patients (Machado et al., 2015; Soubrier et al., 2013). A mutation in the gene KLF2 has been shown by the inventors to cause hereditary PAH (HPAH) (Eichstaedt et al., 2017) and mutations in the gene TBX4 have been identified in several cases of paediatric PAH, idiopathic PAH (IPAH) and HPAH (Levy et al., 2016). Moreover, mutations in two additional genes are now considered responsible for the onset of HHT: the bone morphogenic protein 9 (BMP9 or GDF2) (Wooderchak et al., 2013) and the SMAD Family member 4 (SMAD4) (Toning et al., 2014). HHT often lead to pulmonary arterial hypertension which drastically worsens patients' survival (Lyle et al., 2016).
The inventors have further found that the following set of 43 genes, which comprise the 14 “core genes” (in grey), as well as the set of 15 genes, and further genes are even more preferred for the diagnosis of a genetic predisposition to PAH, PVOD, HHT and partly CTEPH:
The genes ACVRJ, BMP2, BMPR1A, ID1, ID2, ID3, ID4, SMAD5, SMAD6, and SMAD7 (SEQ ID NOs. 15-17, 21-24, 29-31) are part of the BMPR2 pathway.
As discussed above, the genes ACVRL1, BMRP2, ENG (SEQ ID NOs. 1, 3, 6) have been found to be mutated in CTEPH.
As discussed above, the gene EIF2AK4 (SEQ ID NO 5) has been shown to be mutated in PVOD.
As discussed above, the genes ACVRL1, BMPR2, ENG, GDF2, SMAD4 (SEQ ID NOs. 1, 3, 6, 7, 12) have been shown to be mutated in HHT.
The genes CREB1, FOXO1, HRG, IL6, KLF4, KL5, VCAN, and ZFYVE16 (SEQ ID NOs. 18-20, 25-27, 34, 36) are known from PAH animal models.
The gene NOTCH3 (SEQ ID NO. 28) is involved in pediatric PAH manifestation.
The gene SOD2 (SEQ ID NO. 32) is known from a PH animal model and is epigenetically changed in PAH patients and PH animal model.
The gene THBS1 (SEQ ID NO. 33) is involved in hereditary PAH (HPAH) manifestation.
The gene VHL (SEQ ID NO. 35) is known from a PH animal model and involved in Chuvash-associated PAH (Chuvash-APAH) manifestation.
The gene BTNL2 (SEQ ID NO. 37) is involved in sarcoidosis associated PAH.
The gene CYP1B1 (SEQ ID NO. 38) has a decreased expression in BMPR2 mutation carriers.
The gene EPAS1 (SEQ ID NO. 39) is involved in HPAH manifestation and is associated with erythrocytosis.
The gene JAK2 (SEQ ID NO. 40) is involved in myeloproliferative disease (MDS) and chronic thromboembolic pulmonary hypertension (CTEPH).
The genes TBX2 and TBX4 (SEQ ID Nos. 41-42) are involved in pediatric PAH manifestation associated with microcephaly thyroid and sensorineural abnormalities or small patella syndrome.
The gene TMEM70 (SEQ ID NO. 43) is involved in persistent neonatal PAH with ATPase synthase deficiency.
In one embodiment the following set of 36 genes, which comprise the 14 “core genes” (in grey) and further genes are preferred for the diagnosis of a genetic predisposition to PAH and partly CTEPH, PVOD and/or HHT:
The diagnosis of genetic defects/a genetic predisposition comprises sequencing of target genomic regions of the genes of the gene panel, which can be the exons (preferably all the exons), exon-intron boundaries of the genes, and/or base pairs at the 5′ and 3′ untranslated region (UTR).
Said sequencing is preferably carried out or comprises next generation sequencing.
“Next generation sequencing” refers to high-throughput sequencing based on different technologies, which enable the generation of a great amount of sequence data in a short time frame opposed to the conventional, slower and more expensive direct Sanger sequencing.
Next-generation sequencing (NGS), also known as high-throughput sequencing, include e.g. the following sequencing technologies:
These recent technologies allow to sequence DNA and RNA more quickly and cheaply than the previously used Sanger sequencing.
In one embodiment, the diagnosis optionally further comprises an additional sequencing, preferably Sanger sequencing, or an analysis technique, preferably multiplex ligation-dependent probe amplification (MLPA) or quantitative polymerase chain reaction (quantitative PCR).
In embodiments where large(r) deletions or insertions in the PAH/CTEPH genes are determined, an additional analysis technique (such as MLPA or quantitative PCR) is useful for confirmation.
The sample(s) is/are patient sample(s) or sample(s) from a relative of a PAH/CTEPH patient or a PAH/CTEPH/PVOD/HHT patient, respectively.
The terms “PAH/CTEPH patient” and “PAH/CTEPH/PVOD/HHT patient” are used interchangeably throughout the specification.
In one embodiment, at least two (patient) samples are tested simultaneously. A (patient) sample is preferably whole blood, peripheral blood or tissue.
In further embodiments a higher number of (patient) samples are tested, such as up to e.g. 48 samples, 96 samples or up to 384 samples. The number of samples depends also on the type of sample plate used as well as on the type of sequencer.
The gene panel or combination of genes of the present invention can preferably be used for diagnostic genetic testing in subjects, preferably in PAH/CTEPH/PVOD/HHT patients and/or its family members.
Said diagnosis includes determining whether one mutation in the respective genes is present or a second mutation in terms of one or more altered base pairs, smaller and larger deletions or insertions, wherein said mutation(s) is/are genetic confirmation of manifest or existing PAH or indicative for the increased probability for PAH/CTEPH/PVOD/HHT to occur or manifest in not yet affected family members of PAH/CTEPH/PVOD/HHT patients. Patients with mutations have been shown to have more severe symptoms and shorter survival (Evans et al., 2016), and thus these patients may be checked on their clinical symptoms in shorter intervals and their family members may be invited for genetic counselling and testing.
The gene panel or combination of genes of the present invention can preferably be used for screening of newborns, such as of babies/newborns of patients with PAH/CTEPH/PVOD/HHT or their family members, but also in a general newborn screening. The early detection of mutations may enable an early diagnosis and treatment as soon as symptoms occur.
The gene panel or combination of genes of the present invention can preferably be used for pre-implantation diagnostics, as currently offered in e.g. France (Girerd et al., 2015). In particular in families, in which the disease penetrance is high, i.e. in which many mutation carriers develop the disease, pre-implanation diagnostics may be applied within the legal framework.
As discussed above, the present invention provides a method for the diagnosis pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH), in particular for the diagnosis of genetic defects in PAH and/or CTEPH.
Preferably, the diagnosis of genetic defects in pulmonary arterial hypertension comprises the diagnosis for pulmonary veno-occlusive disease (PVOD) and/or hereditary haemorrhagic telangiectasia (HHT).
Said method comprises the following steps:
The sample(s) provided in step (a) is/are patient sample(s) or sample(s) from a relative of a PAH/CTEPH patient or a PAH/CTEPH/PVOD/HHT patient, respectively. Preferably, the (patient) sample is whole blood, peripheral blood or tissue.
As discussed above, the terms “PAH/CTEPH patient” and “PAH/CTEPH/PVOD/HHT patient” are used interchangeably throughout the specification.
In one embodiment, in step (c) the presence of at least one mutation in terms of one or more altered base pairs, smaller and larger deletions or insertions in the 14 genes with the nucleotide sequence of SEQ ID Nos. 1 to 14 and in up to 50 genes is determined, wherein said 50 genes comprise the genes with the nucleotide sequence of SEQ ID Nos. 1 to 43. Preferably, a range of at least 14 genes and up to 50 genes are used. In one embodiment 15 genes are used, in one embodiment 36 genes are used, in one embodiment 43 genes are used.
In a preferred embodiment, in step (c) the presence of at least one mutation in terms of one or more altered base pairs, smaller and larger deletions or insertions in the genes with the nucleotide sequence of SEQ ID Nos. 1 to 14 and 42.
In one embodiment, in step (c) the presence of at least one mutation in terms of one or more altered base pairs, smaller and larger deletions or insertions in the genes with the nucleotide sequence of SEQ ID Nos. 1 to 36 is determined.
In a preferred embodiment, in step (c) the presence of at least one mutation in terms of one or more altered base pairs, smaller and larger deletions or insertions in the genes with the nucleotide sequence of SEQ ID Nos. 1 to 43 is determined.
In one embodiment, the presence of at least two mutations in terms of one or more altered base pairs, smaller and larger deletions or insertions is indicative for the existence of PAH or the increased probability for PAH to become manifest.
In one embodiment, in step (b) the genomic DNA is extracted from peripheral blood using procedures known in the art.
Preferably, at least two (patient) samples are tested simultaneously. In further embodiments a higher number of (patient) samples are tested, such as up to e.g. 48 samples, 96 samples or up to 384 samples. The number of samples depends also on the type of sample plate used as well as on the type of sequencer.
The genomic DNA can be tagged, such as with a barcode. The DNA of each patient/each subject can be tagged differently allowing multiple samples to be tested in parallel/simultaneously.
The genomic DNA can be digested e.g. with restriction enzymes and the desired genes can be captured by 50 to 500 bp biotinylated probes annealing to the respective genomic sequence. The pull-down of desired fragments can be achieved via biotin-streptavidin beads. The fragments can be amplified via PCR and loaded onto a sequencer for sequencing.
In one embodiment, the method comprises the further step of
In embodiments where large(r) deletions or insertions in the PAH/CTEPH/PVOD/HHT genes are determined, an additional analysis technique (such as MLPA or quantitative PCR) is useful for confirmation.
In one embodiment, the method is used for
As discussed above, the present invention provides a kit for the diagnosis of pulmonary arterial hypertension (PAH) and/or chronic thromboembolic pulmonary hypertension (CTEPH), in particular for the diagnosis for a genetic predisposition to PAH and/or CTEPH.
Preferably, the diagnosis of genetic defects in pulmonary arterial hypertension comprises the diagnosis for pulmonary veno-occlusive disease (PVOD) and/or hereditary haemorrhagic telangiectasia (HHT).
Said kit comprises
In one embodiment, the means (i) are means for carrying out next generation sequencing and detecting at least one such mutation in the genes with the nucleotide sequence of SEQ ID Nos. 1 to 14 and 42.
In one embodiment, the means (i) are means for carrying out next generation sequencing and detecting at least one such mutation in the genes with the nucleotide sequence of SEQ ID Nos. 1 to 36, preferably in the genes with the nucleotide sequence of SEQ ID Nos. 1 to 43.
Said means comprise probes suitable for sequencing target genomic regions of the respective genes and for determining whether at least one such mutation in said genes is present.
Said target genomic regions can be the exons (preferably all the exons), exon-intron boundaries of the genes, and/or base pairs at the 5′ and 3′ untranslated region (UTR).
Said probes can have a length of 50 to 500 nucleotides. Said probes can be labelled, such as via biotin, and/or fluorophores.
Said means can, for example, be designed and generated using HaloPlex technology or SureSelectXT technology (Agilent Technologies, Santa Clara, USA) or using the in silico tool SureDesign (Agilent Technologies, Santa Clara, USA).
Said kit can optionally further comprise
Said processing means can be for tagging, digesting, capturing etc.
The genomic DNA can be tagged, such as with a barcode. The DNA of each patient can be tagged differently allowing multiple samples to be tested in parallel/simultaneously.
The genomic DNA can be digested with e.g. restriction enzymes and the desired genes can be captured by 50 to 500 bp biotinylated probed annealing to the respective genomic sequence. The pull-down of desired fragments can be achieved e.g. via biotin-streptavidin beads.
The fragments can be amplified via PCR and loaded onto a sequencer for sequencing.
Said kit optionally further comprises
Said means (iii), for example, comprise dNTPs, polymerases, buffer, magnesium chloride, specific primers and probes.
In embodiments where large(r) deletions or insertions in the PAH/CTEPH/PVOD/HHT genes are determined, an additional analysis technique (such as MLPA or quantitative PCR) is useful for confirmation.
In this study we developed a new specific gene panel for pulmonary arterial hypertension (PAH), chronic thromboembolic pulmonary hypertension (CTEPH), pulmonary veno-occlusive disease (PVOD) and hereditary haemorrhagic telangiectasia (HHT) including major disease genes and further candidates. The new PAH-specific gene panel developed in this study allowed for the first time the assessment of all known PAH genes and further candidates at once and markedly reduced overall sequencing time and costs. Sensitivity and specificity reached 100% when Sanger technique was additionally applied. Thus, this technique will potentially change the routine diagnostic genetic testing in PAH patients.
We developed a PAH/CTEPH/PVOD/HHT-specific gene panel based on NGS and tested sensitivity and specificity including 43 PAH/CTEPH/PVOD/HHT genes and candidates in up to 96 patients and family members. A pilot study, including 29 genes, revealed BMPR2, ALK1, ENG and EIF2AK4 mutations in 59% of patients and documented a 100% sensitivity and 100% specificity of the panel, when Sanger technique was additionally applied in a “two step” procedure. The study showed that mutations in “new” genes such as EIF2AK4 could be frequently detected in PAH patients which would have been overlooked by the commonly used standard procedure addressing the 3 major PAH/CTEPH/PVOD/HHT genes (BMPR2, ALK1, ENG) only. Therefore, this technique will completely change the usual molecular diagnostic approach. NGS enables the screening of many genomic regions at once, Sanger sequencing of the pathologic variants as second step enables a 100% specificity.
Very recently another study was published by Piao and colleagues (2016) investigating mutations in 22 PAH associated genes in a cohort of IPAH/HPAH patients. They could only identify mutations in the genes BMPR2 and ALK1 in 25% of the patients. No mutations in other candidate genes were uncovered. While 11 genes overlapped with our panel we also present data for 34 distinct candidate genes. EIF2AK4 was not sequenced by Piao et al. and thus potential mutations might have been overlooked. This exemplifies how crucial the selection of candidate genes is to detect PAH causing mutations.
The PAH/CTEPH-specific gene panel is much more time and cost efficient than the conventional Sanger sequencing. The time per patient can be drastically reduced even further with different hardware analysing up to 96 patients at once. The number of genes could be increased up to 50, albeit lowering the average coverage of analysed genes.
The newly developed panel generates results for all genes in the same process. In contrast, Sanger sequencing is performed sequentially, one gene at a time. Hence, Sanger sequencing would be terminated as soon as a single mutation was identified excluding the possibility of detecting additional mutations as second hits (Rodriguez Viales et al., 2015). Therefore, a similar NGS panel approach is already in use for common diseases such as familiar breast and ovarian cancer (Schroeder et al., 2015).
Alternatively to Sanger technique whole exome NGS has been previously applied in PAH patients and detected 4 new PAH genes: the membrane protein caveolin-1 (Austin et al., 2012), the potassium channel KCNK3, the translation factor EIF2AK4 and the topoisomerase binding protein TOPBP1 (de Jesus Perez et al., 2014). However, whole exome NGS requires such an enormous amount of work (approximately several months to identify putative PAH genes in one patient) in teams of bioinformatics analyses, data processing and storage that this technique is currently no option for the routine diagnostic setting. It is only feasible for scientific use.
Additional 5 candidate genes identified with conventional methods included BMPR1B (Chida et al., 2012), KCNA5 (Remillard et al., 2007), SMAD1 (Nasim et al., 2008), SMAD4 (Nasim et al., 2008) and SMAD9 (Shintani et al., 2009). These genes represent the most promising candidates to be mutated in IPAH/HPAH patients with no mutations in BMPR2, ENG or ALK1 (Kwapiszweska et al, 2014). Hence, a targeted screening of all of these genes increases the probability of a disease causing mutation to be detected. Moreover, the continuous inclusion of putative candidate genes in the same panel will advance our knowledge of the PAH aetiology and highlight new genes involved in disease manifestation. The new PAH/CTEPH/PVOD/HHT-specific gene panel presented in this application will allow to better identify additional mutations, acting as modifiers for disease manifestation.
Genetic assessment might receive a more prominent role within the actual and future diagnostic algorithm as indicated in the new ESC/ERS-guidelines and may even be useful for risk stratification. At the same time, the use of the PAH/CTEPH/PVOD/HHT-specific gene panel diagnostic requires a more comprehensive genetic counselling before and after the molecular analysis, since more genes are analysed and variants of unknown significance will also have to be explained. Once mutations have been identified in PAH/CTEPH/PVOD/HHT patients the genetic assessment and counselling of family members is furthermore complicated by the yet unknown penetrance of mutations in less common PAH genes (Girerd et al., 2016).
Both newly identified heterozygous mutations of the pilot study were located within EIF2AK4. Mutations in EIF2AK4 have been previously described in families with PVOD (Eyries et al., 2014) and pulmonary capillary haemangiomatosis (Best et al., 2014). Whereas we included one patient with PVOD this patient showed no mutation or variant in EIF2AK4 but a BMPR2 mutation. Recently, mutations in EIF2AK4 were also identified in 5 families of an Iberian population suffering from an aggressive form of HPAH (Tenorio et al., 2014) and two additional families (Gomez et al., 2015). Thus, this is the third study reporting mutations of EIF2AK4 in I/HPAH-patients.
Twelve variants were classified as variants of unknown significance in a pilot study analysing a subset of 29 genes in 37 patients and 5 family members of other PAH patients since not all in silico prediction programmes characterised them as “pathogenic” and/or they were present in a public database. Nevertheless, variants, which were classified as “pathogenic” by at least one prediction programme and are absent in non-PAH patients, represent interesting follow-up candidates for functional studies such as the variants in exon 23 of EIF2AK4, in exon 3 of SMAD7 or in SMAD6 exon 4. Due to the low frequency of PAH in the population (15:1,000,000) already two individuals with the same variant in the public ExAC database rise the population frequency of the variant above 0.0015%, the conservative cut-off expected for mutations causing PAH (Machado et al., 2015). Considering this level, a variant at a frequency of 0.0016%, which occurs in two individuals in the database, such as the variant in exon 3 of the VCAN gene might still represent an interesting follow-up candidate.
The new approach of a panel diagnostic including a vast array of PAH/CTEPH/PVOD/HHT associated genes has shown to have a high sensitivity and specificity together with confirmatory Sanger sequencing. In already a small subset of patients two mutations in EIF2AK4 were identified, which would have not been detected with the previous routine procedure. Therefore, for patients and for practitioners this approach offers a comprehensive, cost and time efficient way to investigate genetic influences of PAH/CTEPH/PVOD/HHT and can be continuously adapted to include newly detected causative PAH/CTEPH/PVOD/HHT genes.
1) The inventors have found evidence that in some patients at least 2 gene defects are necessary for disease manifestation (second hit hypothesis) (Eichstaedt et al., 2016; Rodriguez Viales et al., 2015).
Mutations in the EIF2AK4 gene have recently been identified in recessively inherited VOD. In this study we assessed if EIF2AK4 mutations occur also in a family with autosomal dominantly inherited pulmonary arterial hypertension (HPAH) and incomplete penetrance of BMPR2 mutations.
Clinical examinations in a family with 10 members included physical examination, electrocardiogram, (stress)-echocardiography and lung function. Manifest PAH was confirmed by right heart catheterisation in three affected subjects. Genetic analysis was performed using a new PAH-specific gene panel analysis with next generation sequencing of all known PAH and further candidate genes. Identified variants were confirmed by Sanger sequencing.
All living family members with manifest HPAH carried two pathogenic heterozygous mutations: a frame shift mutation in the BMPR2 gene and a novel splice site mutation in the EIF2AK4 gene. Two family members who carried the BMPR2 mutation only did not develop manifest HPAH.
This is the first study suggesting that EIF2AK4 can also contribute to autosomal dominantly inherited HPAH. Up to now it has only been identified in a recessive form of HPAH. Only those family members with a co-occurrence of two mutations developed manifest HPAH. Thus, the EIF2AK4 and BMRPR2 mutations support the “second hit” hypothesis explaining the variable penetrance of HPAH in this family. Hence, the assessment of all known PAH genes in families with a known mutation might assist in predictions about the clinical manifestation in so far non-affected mutation carriers.
This is the first report of an autosomal dominantly inherited EIF2AK4 mutation as second hit in a family with HPAH and known BMPR2 mutation. Only those family members with a co-occurrence of a mutation in BMPR2 and EIF2AK4 were clinically affected and developed manifest HPAH, whereas carriers of the BMPR2 mutation only had no symptoms of PAH. Thus, the results of this study offer an explanation for the reduced penetrance of the disease in this family and show that EIF2AK4 may play a role also in families with autosomal dominantly inherited PAH.
EIF2AK4 was first described in the autosomal recessively inherited pulmonary veno-occlusive disease (PVOD) (Eyries et al., 2014) and pulmonary capillary haemangiomatosis (Best et al., 2014). Recently a single recessively inherited EIF2AK4 mutation (c.3344C>T, p.(P115L)) was repeatedly identified in six consanguineous HPAH families with autosomal recessive mode of inheritance (Gomez et al., 2014; Tenorio et al., 20105). Only homozygous mutation carriers developed the disease plus a single heterozygous carrier of a distinct EIF2AK4 mutation, in whom the authors suspected a second non-identified mutation in the same gene (Gomez et al., 2015). Therefore, up to now EIF2AK4 mutations have been believed to be a very rare in HPAH. Apart from the mentioned family we were able to identify a nonsense mutation in exon 8 in the EIF2AK4 gene in another PAH patient with sporadic IPAH who had no other mutation in known candidate genes (data not shown). Thus, this gene might be more often affected than initially thought and contributes to the disease in an autosomal dominant manner. In contrast, BMPR2 mutations occur in up to 85% of familial cases and are autosomal dominantly inherited (Machado et al., 2015; Pfarr et al., 2011). However, many BMPR2 gene carriers have no clinical symptoms and do not develop manifest PH even during a more than 10 year follow-up period (Hinderhofer et al., 2014). Hence, the family described here provides an explanation for the decreased penetrance and suggests an autosomal dominantly contribution of EIF2AK4 to disease manifestation.
Up to date only four families with second hits have been described (Rodriguez Viales et al., 2015; Wang et al., 2014). This might be due to the fact that usually only 3 genes (BMPR2, ACVRL1, ENG) are analyzed routinely in PAH patients in a sequential processes, i.e. if one mutation is discovered the other genes are not assessed. Thus, second hit mutations might be overlooked in general in the current routine diagnostic setting and particularly in genes such as EIF2AK4, which are usually not included in the diagnostic analysis.
While second hits are still rarely described in PAH this model is often found in other diseases such as the nephrotic syndrome or the long QT-syndrome. At the same time the decreased penetrance in PAH is an acknowledged pattern. Thus, second hits or modifier genes might be more common in PAH than known to date. We therefore contrast two genetic models: Firstly, we propose the “second hit model” to explain the low disease penetrance in PAH. In this model a single mutation in each gene on its own has a very low penetrance. Two mutations however, lead to a synergistic effect resulting in a high disease penetrance. The second model is the “single gene model”, representing the classical view for PAH suggesting BMPR2 mutations alone are responsible for disease manifestation. Under this assumption, the EIF2AK4 mutation would randomly occur in this family and not impact PAH manifestation. In the latter model the penetrance for the BMPR2 variant must be moderate, since 4 (obligate) carriers of the mutation did not develop PAH up to ages 31, 37, 49 and 59.
Considering both models, it is significantly unlikely that both mutations in two known PAH genes occurred by chance in this family. Moreover, the EIF2AK4 mutation clearly co-segregates with the disease in BMPR2 positive family members suggesting a second hit model.
We have not observed an EIF2AK4 mutation alone within this family, albeit in a different IPAH patient (data not shown) indicating at least a low penetrance to be present. Disease severity might moreover be influenced by the location of the respective mutations within the protein and thus their variable impact on protein function (Machado et al., 2015). Therefore, we hypothesize according to the second hit model the penetrance to be intermediate if only BMPR2 was positive, very low if only EIF2AK4 was positive, and very high if EIF2AK4 and BMPR2 each harbor a mutation.
The gene EIF2AK4 encodes a kinase termed general control nonderepressable 2 (GCN2) which phosphorylates the eukaryotic translation initiation factor 2α leading to a global down regulation of protein synthesis in response to amino acid starvation, hypoxia and viral infection but the up-regulation of specific stress response proteins (Montani et al., 2016). Gene expression is increased in smooth muscle cells in the vessel wall and interstitial tissue (Eyries et al., 2014). While the gene function has been studied a clear link to PVOD or PAH still remains to be detected. However, an interaction between EIF2AK4 and the BMPR2 pathway genes SMAD1, SMAD4, ACVRL1 and ENG has been observed (Barrios-Rodiles et al., 2005; Eyries et al., 2014). Thus, an impaired functioning of both, BMPR2 and GCN2 (EIF2AK4), might potentiate its effect on the transcription of target genes of the BMPR2 pathway.
The EIF2AK4 mutation of this family leads to the loss of a splice site and subsequently the loss of exon 38, presumably a frame shift and premature stop codon. In the last exons of the functional gene (31-39) lies the ribosomal binding domain and the dimerisation domain between amino acids 1396-1643 (Padayana et al., 2005). The last 51 amino acids of this domain were missing or partly exchanged by wrong amino acids in the affected members of this HPAH family. The domain is essential to recruit ribosomes for protein synthesis (Narasimhan et al., 2004), thus a partial deletion will at least moderately affect protein-ribosome binding if not fully impair it. Moreover, in the same region the dimerisation domain is located. This facilitates the formation of a homodimer (2 EIF2AK4 proteins bind to each other) and thus a functional protein (Narasimhan et al., 2004). The formation of homodimers has been shown to be conserved in mice and yeast (He et al., 2014). Single amino acid substitutions in the C-terminal domain in yeast already led to an inability of the protein to dimerise and to be functionally active (Narasimhan et al., 2004). The gene sequence of the C-terminal domain is highly conserved from mice to mammals suggesting corresponding functional impairments in humans (Berlanga et al., 1999). A total deletion of this region in our HPAH family thus likely leads to a loss of function in the mutated gene.
We were able to show EIF2AK4 contributes to disease manifestation in this HPAH family in an autosomal dominant manner. We report a new mutation within EIF2AK4 leading to HPAH as a second hit together with a mutation in BMPR2 providing an explanation for the observed penetrance in this family. Only those family members with a co-occurrence of two mutations developed manifest HPAH. The occurrence of several mutations in PAR associated genes might be more frequent than initially thought. Thus, a simultaneous assessment of all PAH associated genes in more patients might shed light on the long standing question surrounding the reduced penetrance.
2) A mutation in the gene KLF2 has been shown by the inventors to cause hereditary PAH (HPAH) (Eichstaedt et al., 2017).
Heritable pulmonary arterial hypertension (HPAH) is an autosomal dominantly inherited disease caused by mutations in the BMPR2 gene and/or genes of its signalling pathway in approximately 85% of patients. We clinically and genetically analysed an HPAH family without mutations in previously described PAH genes. Clinical assessment included electrocardiogram, lung function, blood gas analysis, chest X-ray, laboratory testing, echocardiography and right heart catheterization in case of suspected disease. Genetic diagnostics were performed using a PAH-specific gene panel including all known 12 PAH genes and 20 further candidate genes by next-generation sequencing (NGS). HPAH was invasively confirmed in two sisters and their father who died aged 32 years. No signs of HPAH were detected in five first-degree family members. Both sisters were lung transplanted and remained stable during a follow-up of >20 years. We detected a novel missense mutation in the Krüppel-like factor 2 (KLF2) likely leading to a disruption of gene function. The same KLF2 mutation has been described as a recurrent somatic mutation in B-cell lymphoma. Neither the healthy family members carried the mutation nor >120000 controls. These findings point to KLF2 as a new PAH gene.
In this study we detected a novel germline mutation in the KLF2 gene likely causing autosomal inherited HPAH in a family with three affected patients, a follow-up of >20 and no mutations in any of the previously described 12 PAH genes. The identification of KLF2 as potential PAH gene will generate new insights into the pathogenesis of the disease since it regulates pathways which have been shown to be involved in PAH development such as cell proliferation, inflammation and vasodilation.
KLF2 is a promising PAH gene, as Krüppel-like factors play an important role in many cellular functions which are also involved in the disease aetiology of HPAH. The pathogenicity of the detected KLF2 mutation was supported by several levels of evidence. Firstly, the functional spectrum of the KLF2 transcription factor, in particular its implication in endothelial activation and proliferation (Bhattacharya et al., 2005) and regulation of vasotonus points to an involvement in the development of PAH. Since KLF2 is able to inhibit a driver of endothelial cell proliferation, the VEGF receptor 2 (Bhattacharya et al., 2005), mutations which impair KLF2 functioning, may also lead to an increased cell proliferation. Similarly, functional KLF2 downregulates vasoconstrictors such as endothelin-1 and upregulates vasodilators such as eNOS (Dekker et al., 2005). Hence, a disturbance in this regulation is likely increasing vascular tonus, which is also observed in PAH.
Secondly, the mutation is significantly associated with PAH and co-segregated with the disease in our family. It has not been described before in PAH and was absent in unaffected family members as well as more than 120,000 controls.
Thirdly, the same mutation has been identified in splenic marginal zone lymphoma (Clipson et al., 2015) and functional studies clearly indicated a displacement from the nucleus and reduced transcriptional activity (Piva et al., 2015). The lymphoma-associated mutations have been identified as somatic mutations, whereas the presumption in this study is that the KLF2 mutation is a germline event and thus present during development. This is a critical distinction, as homozygous germline deletion of KLF2 in mice has been published to be embryonic lethal or at least very deleterious to normal embryonic development (Yeo et al., 2014). The mechanism of embryonic lethality relates in part to loss of vascular integrity, lending some additional biological plausibility to KLF2 as a PAH-related gene. However, the published data suggest a specific activity of the mutant that is strongly reduced compared to the wild-type (Piva et al., 2015). This would fit with an incompletely penetrant, embryonically viable mutation that nonetheless manifests in disease. Thus, considering all evidence it is highly likely that the KLF2 mutation in this family led to PAH manifestation.
A closer review of KLF2 functionality and cellular localisation revealed a tight connection to the BMPR2 signalling pathway (
The findings of this study highlight for the first time KLF2 as a potential PAH gene. KLF2 functions are closely tied to the disease aetiology of PAH as it regulates vasotonus, cell proliferation and endothelial activation and the gene is linked to the BMPR2 pathway.
The following examples and drawings illustrate the present invention without, however, limiting the same thereto.
(A) In the first step the panel is designed in silico. The customised panel is manufactured and the desired PAH/CTEPH/PVOD/HHT genes are extracted from DNA of PAH/CTEPH patients and family members. PAH/CTEPH/PVOD/HHT genes from each patient are enriched leading to a high coverage of the regions of interest allowing 100% sensitivity to detect all true positive variants. Samples are pooled and loaded together onto a next generation sequencer.
(B) Resulting data is passed through quality control, the reads are aligned to a reference sequence and any variant from polymorphisms to mutations is identified. These variants are assessed regarding their clinical significance with comparative data bases and in silico prediction programs. To eliminate false positives direct Sanger sequencing is applied in a second sequencing step reaching 100% specificity.
Next to the ladder the affected individual 11:4 shows a heterozygous PCR product for the cDNA of EIF2AK4 exons 36-39. The upper band shows the wildtype sequence (266 bp) while the lower band shows a product without exon 38 (147 bp). The healthy family member III:4 is homozygous for the wild type PCR product indicating no loss of exon 38.
KLF2 is upregulated by laminar blood flow, apelin and the bone morphogenic protein 4 (BMP4), which binds to the dimerised BMP receptor 2 (BMPR2) and the activin receptor like kinase (ALK or ACVRL1). Signals are transduced via the adenosine monophosphate kinase (AMPK), the mitogen activated protein kinase kinase 5 (MEKS or MAP2K5) and subsequently the extracellular signal regulated kinase 5 (ERKS or MAPK7). Apelin transcription is down regulated by BMP4, 7 and 9 orchestrated via the sma- and mad-related (SMAD) pathway. In contrast, BMP2 is able to induce apelin expression via the nuclear complex beta-catenin and peroxisome proliferator-activated receptor gamma (PPARγ). Thus, the BMPR2 pathway can directly activate KLF2 and regulate apelin (APLN), an upstream regulator of KLF2. The KLF2 transcription factor inhibits endothelin-1 (ET-1 or EDN1) and vascular endothelial growth factor receptor 2 (VEGFR2 or KDR) expression while increasing endothelial nitric oxide synthase (eNOS or NOS3) transcription. These effects lead to a reduction in endothelial cell proliferation, the generation of NO and subsequent vasodilation of pulmonary artery smooth muscle cells (PASMCs). With a dysfunction of the KLF2 gene caused by a germline mutation as detected in this study, several PAH pathways will be activated. (Eichstaedt et al., 2017).
In all PAH patients of the pilot study diagnosis was performed according to current ERS/ESC-guidelines. All patients underwent a detailed clinical examination including right heart catheterisation as described previously (Grünig et al., 2009). Testing for vasoreactivity and left heart catheterisation were performed when clinically indicated. Clinical assessment of family members included taking medical history, lung function, six minute walking distance, physical examination, 12-lead electrocardiogram, echocardiography at rest and during supine bicycle exercise (Grünig et al., 2009; Kabitz et al., 2008). Acute or chronic pulmonary and cardiac diseases were ruled out in all family members. Blood samples were collected from all patients and relatives of other PAH patients. The protocol of this study confirms to the ethical guidelines of the Declaration of Helsinki. It was approved by the Ethic Committee of Heidelberg University and participants or their parents gave written informed consent.
We developed a technique which in general would allow to asses up to 50 genes in up to 96 patients/family members simultaneously. In brief, after DNA is extracted, genomic regions of interest were enriched with a self-designed customised PAH panel, sequenced with NGS and possible pathogenic variants confirmed with targeted Sanger sequencing (
The new gene panel was manually designed with the in silico tool SureDesign (Agilent Technologies, Santa Clara, USA). While the gene panel may assess up to up to 50 genes in 96 patients we concentrated on 43 genes and 37 patients and 5 relatives of other PAH patients to evaluate the sensitivity and specificity of this approach in the presented pilot study.
For this pilot study, a list of 29 genes including 12 PAH causal genes, was created after extensive literature research (Table 1 lists these 29 genes). The respective genomic regions, i.e. all exons plus 25 base pairs at 5′ and 3′ untranslated region and adjacent exon-intron boundaries, were extracted in silico from the human genome (GhR37/hg19). Subsequently, probes were designed which covered each single DNA base within the desired genomic regions by on average of 7 different probes. Based on the in silico design a customised gene panel was manufactured by Agilent Technologies (HaloPlex).
DNA from subjects was extracted from peripheral blood using standardised procedures (Qiagen, Hilden, Germany) and tagged with a bar code allowing multiple samples to be included in a single run. The library preparation in vitro included DNA digestion by 16 restriction enzymes and the capture of the desired target genes by biotinylated probes. After pull down of desired fragments with biotin-streptavidin beads fragments were amplified by PCR and loaded onto the MiSeq (Illumina, San Diego, USA) for subsequent sequencing. The kit may either be used entirely in one run on a NGS machine or split up in several runs. The latter option was used for the MiSeq and we performed four runs with 9-12 patients each.
Data was imported into SeqPilot 4.1.2 (JSI medical systems GmbH, Kippenheim, Germany). Transcripts were loaded using the GhR37/hg19 automated feature. Regions of interest were defined as coding exons including 20 base pairs of the 5′ and 3′ untranslated region. Default parameters were altered to highlighted changes in the sequence when >20 reads covered the specific base pair to account for non-random distributed reads over target regions in the HaloPlex design (Schroeder et al., 2015).
While heterozygosity in Sanger sequencing is characterised by an equal frequency of the two variants, NGS is based on probes which amplify regions of interest. Differential amplification of specific probes might lead to a skewed ratio of the two variants. The initial heterozygosity cut-off of 35% to 65% for the two respective alleles was lowered to ≥10% and potential pathogenic variants were re-assessed with Sanger sequencing.
Each variant was classified as either clearly benign (polymorphism), likely benign, uncertain significance, likely pathogenic or clearly pathogenic as recommended by the Human Genome Variation Society (HGVS, http://www.hgvs.org/) (Richards et al., 2015). Each variant was evaluated in terms of minor allele frequency (MAF) in ENSEMBL and absolute frequency in the Exome Aggregation Consortium (ExAC) including more than 60,000 exomes from unrelated individuals (Lek et al., 2016). The consideration of this large database can prevent common variants from being classified as disease causing (Granzow et al., 2015). Polymorphisms were defined as a MAF≥5% (Richards et al., 2015). All variants with a MAF<5% were sought in the Human Gene Mutation Database (HGMD Professional 2015.4). Additionally, for variants of BMPR2, ENG, ALK1 and SMAD4 present in the ARUP data base (http://www.arup.utah.edu/database/) a literature search was conducted. Non-synonymous missense variants with MAF<5% were characterised using four in silico prediction programmes: MutationTaster, SIFT, Align GVGD and PolyPhen2 implemented in Alamut 2.7.1 (interactive biosoftware, Rouen, France). Variants were considered as likely pathogenic in case of non-sense, frameshift and splice site mutations not occurring in the last exon of a gene (Wallis et al., 2013) and are tetmed mutations hereafter. Variants which could not be clearly assigned with the majority of the in silico prediction tools were classified as having an “uncertain significance”.
All variants of uncertain significance, likely pathogenic variants or mutations were reanalysed with Sanger sequencing after designing specific primers and evaluating the optimal polymerase chain reaction (PCR) conditions.
Sensitivity and the specificity were estimated using BMPR2, ALK1 and ENG genes fully sequenced with Sanger and NGS technique. Sensitivity is defined in our case as the percentage of mutations identified by Sanger (gold standard) which were also detected by NGS. By the set-up of NGS being followed by Sanger validation this two-step procedure has a specificity of 100%, since all NGS false positives are removed in the Sanger validation step.
Patients who showed no mutations within BMPR2, ALK1 or ENG were additionally assessed with multiplex ligand-dependent probe amplification (MLPA, it P093-C1, MRC-Holland, Amsterdam, Netherlands) to detect large deletions or duplications encompassing exonic regions of BMPR2, ALK1 and ENG.
Suspected splice site mutations were investigated on RNA level. RNA was extracted following standard procedures. Complementary DNA was generated with a reverse transcriptase assay. Exons of interest were amplified in samples and controls with PCR and splice site alterations were visualised by agarose gel electrophoresis and Sanger sequencing; conditions are available upon request.
We included 37 patients and 5 first degree family members of affected individuals in the panel. Of the patients 19 suffered from IPAH, 8 had HPAH, one patient had PAH associated with congenital heart defects (CHD-APAH) and one patient APAH with pulmonary veno-occlusive disease. Eight patients had PAH and hereditary haemorrhagic telangiectasia (HHT) (Table 2). In the 5 family members no pulmonary hypertension or any other cardio-pulmonary disorder has been detected.
Table 3 summarises the main clinical findings in the 37 PAH patients. Patients had severe PAH with impaired right ventricular function, lung function, lowered oxygen saturation and elevated NT-proBNP levels.
Two new heterozygous mutations in EIF2AK4 gene were identified in a H/IPAH patient, respectively. The first EIF2AK4 mutation led to an introduction of a stop codon (exon 8, c.933T>A p.(Y311*)). The second EIF2AK4 mutation (exon 38, c.4892+1G>T) led to a loss of a splice site and subsequent RNA analysis confirmed the loss of exon 38. Twelve UVs were identified in the following PAH genes: EIF2AK4, HRG, SMAD1, SMAD4, SMAD6, SMAD7 and VCAN (Table 5). Of the 12 UVs, four have not yet been identified in healthy individuals. However, these variants were only classified as “pathogenic” by 1-2 of the four in silico prediction programmes.
The first of four runs of the panel diagnostic experienced technical errors during the sequencing by synthesis on the MiSeq; only 0.8 gigabases (Gb) were sequenced albeit with an average base call error rate≤0.1% (≥Q30) of 91.2%. This drastically reduced the overall coverage leading to a lack of detection of 2 mutations previously identified with Sanger sequencing. These errors were clearly visible in quality parameters during sequencing and were addressed in the subsequent runs (run 2: 5.5 Gb, ≥Q30=90.5%; run 3: 5.8 Gb, ≥Q30=92.1%; run 4: 5.4 Gb, ≥Q30=90.6%). Hence, 100% sensitivity could be obtained in the following runs with an average coverage of approximately 800×. Nevertheless, 14 false positive mutations/variants were initially found with NGS panel which could not be confirmed by Sanger sequencing. These variants were either characterised by “short reads” of 25-36 bp (n=4), a very low heterozygosity of 10-15% (n=5) or other sequencing artefacts (n=5). Several of these artefacts were not confined to single patients and thus clearly identifiable as technical artefacts. Since in routine diagnostics all NGS mutations are verified with Sanger as a second step all false positives would be discovered. Therefore, a specificity of 100 is reached.
With the ultimate goal detecting new variants/mutations in PAH/CTEPH/PVOD/HHT related genes efficiently, the approach of NGS for a specific PAH/CTEPH/PVOD/HHT gene panel enabled highly sensitive, cost- and time-saving sequencing. Technical specifications of the commonly used Sanger sequencing and the new PAH/CTEPH/PVOD/HHT-specific gene panel diagnostic with NGS were compared in Table.
The panel diagnostic in the pilot study allowed sequencing all exons in 29 genes at the same time instead of only one direction of one exon per reaction by Sanger. Not only each exon has to be sequenced separately with Sanger sequencing but also each patient. Meanwhile, the panel diagnostic allows assessing up to 96 patients at the same time albeit keeping the data storage requirements at a moderate level.
The Sanger technique requires approximately 11 h assessment time/per patient for the 3 major PAH/CTEPH/HHT genes BMPR2, ALK1 and ENG. In contrast, the new panel technique in our diagnostic setting allowed the assessment of 29 genes within 5 h assessment time/per patient plus the time required for confirmatory Sanger sequencing. This huge time advantage was enabled by processing several patient samples and PAH/CTEPH/PVOD/HHT genes simultaneously in the laboratory (48 h sample processing in the laboratory for 12 samples at once, see Table 6). While data generation is faster than Sanger sequencing, data analysis and bioinformatics processing is prolonged as any possible pathogenicity of rare variants has to be investigated by in silico prediction programmes and literature research. Nevertheless, once a data base has been established classifying the effect of variants data analysis can be accelerated.
When large deletions and insertions are identified with the PAH/CTEPH/PVOD/HHT-specific gene panel based on NGS, it is preferred to confirm such findings with a second method such as MLPA or quantitative PCR. The PAH/CTEPH/PVOD/HHT-specific gene panel is not limited to the sequence data analysis regarding mutations but also enables the detection of large deletions or insertions in the routine diagnostic setting.
Bold genes indicate 12 of the 14 known PAH genes.
Members of a family with autosomal dominantly inherited HPAH were clinically and genetically assessed. All living genetically related family members were invited to participate in a clinical and genetic evaluation. After written informed consent was obtained family members underwent clinical assessment and genetic counseling. A three generation pedigree was drawn including nine family members of the index patient. EDTA-blood was taken for genetic analysis.
Clinical procedures consisted of recording the family and medical history, physical examination, laboratory parameters including N-type pro brain natriuretic peptide (NT-proBNP), 12-lead electrocardiogram, lung function test, arterial blood gases, 6-minute walking distance, echocardiography, stress-Dopplerechocardiography and cardiopulmonary exercise testing as described previously (Hinderhofer et al., 2014). High resolution computer tomography of the lung was conducted to exclude pulmonary veno-occlusive disease. Left heart catheterisation was performed in all patients with suspected left heart diseases and when clinically indicated. Manifest HPAH was diagnosed according to the current guidelines (Galiè et al., 2016). Right heart catheterisation was performed in the living HPAH patients to confirm diagnosis and for follow-up.
Genomic DNA was isolated from peripheral blood using a salting out procedure (Miller et al., 1988) (Autopure, LGC, Germany). Sanger sequencing for BMPR2 (ENST00000374580) was conducted in the index patient using Big Dye Terminator V1.1 cycle sequencing kit and ABI 3130x1 genetic analyzer (ThermoFisher Scientific, USA). Duplications and deletions were screened by multiplex ligation-dependent probe amplification (MLPA, kit P093-C2, MRC-Holland, the Netherlands).
A new PAH gene panel diagnostic based on next-generation sequencing was designed to analyse second hit mutations in 11 PAH (ACVRL1 or ALK1, BMPR1B, BMPR2, CAV1, EIF2AK4, ENG, KCNA5, KCNK3, SMAD1, SMAD4, SMAD9) and 20 further candidate genes in the index patient. DNA was enriched with a customised SureDesign panel (Agilent Technologies, USA) and sequenced on the MiSeq (Illumina, USA). Exonic regions and exon-intron boundaries were analysed with SeqPilot 4.1.2 (JSI medical systems GmbH, Germany). Variants were characterised following the recommendations of the Human Genome Variation Society (HGVS version 2.15.11) (den Dunnen et al., 2016). Non-synonymous missense variants with a population frequency <5% were assessed regarding their evolutionary conservation, location within functional gene domains and functional consequence using four in silico prediction programs: MutationTaster, SIFT, Align GVGD and PolyPhen2 implemented in Alamut Visual 2.7.1 (interactive biosoftware, France). Variants were confirmed by Sanger sequencing in the index patient and assessed in family members to clarify mutation status. Any variants disrupting gene function were considered mutations.
RNA was isolated from EDTA blood using standard procedures. Copy DNA (cDNA) was generated with a reverse transcriptase reaction adding hexamers for 10 min at 65° C., a cDNA-Mix (Invitrogen, USA) for 2 hours at 37° C. and a final reaction for 10 min at 65° C.
A PCR was designed to assess the cDNA corresponding to the messenger RNA of EIF2AK4 (ENSG00000128829; SEQ ID NO. 5) The PCR product span the exon 38 using a forward primer annealing in exon 36 (5′ GACCTCCCTTGCCAACTTAC 3′; SEQ ID NO. 108) and a reverse primer annealing in exon 39 (5′ AGAT TCTGTAGTAGTCATCTCTATAGC 3′; SEQ ID NO. 109). The expected size of the intact PCR product was 266 bp and the one of the PCR product skipping exon 38 was 147 bp. cDNA was denatured for 5 min at 95° C., and subsequently amplified in 35 cycles (1 min at 95° C., 1 min at 56.5° C., 1 5 min at 72° C.; final elongation 10 min at 72° C.). While several transcripts exist for EIF2AK4 the considered isoform is the most common one in humans since it is referred to as reference sequence by NCBI RefSeq. NCBI RefSeq is a database which we used as reference standard for reporting the location of medically important variations. PCR products were sequenced with Sanger sequencing to identify the altered base pair sequence of the messenger RNA.
Significance of co-occurance of BMPR2 and EIF2AK4 was calculated by using an estimated heterozygote frequency of EIFAK4 mutations retrieved from the Exome Aggregation Consortium (ExAC) database (Lek et al., 2016) and taking into account the number of genes on the panel by correcting for multiplicity. A p-value lower than 5% was considered statistically significant.
Clinical parameters are presented in Table 7. PAH was excluded in healthy family members by regular clinical assessments including physical examination, lung function tests, ECG, and in particular by echocardiography, stress-Doppler-echocardiography, spiroergometry and NT-proBNP values. Diagnosis of PAH was confirmed by right heart catheterisation in patients II:4, III:2 and III:3. The disease was very severe in all three patients but could be stabilised with medication in patients II:4, and Patient III:3 showed a rapid progression and received a lung transplantation 1.5 years after diagnosis. She died only one year after transplantation due to a rejection of the donor organ. Patient II:4 and III:2 were under dual therapy at the time of this writing. Stable haemodynamic parameters were observed in the latest catheter of patient II:4 with a mean pulmonary artery pressure (mPAP) of 46 mmHg, pulmonary arterial wedge pressure (PAWP) of 12 mmHg, cardiac output 4.6 l/min, cardiac index 2.3 l/min/m2 and pulmonary vascular resistance of 591 dynes. Patient III:2 has improved under therapy to a mPAP of 55 mmHg, PAWP of 14 mmHg, cardiac output 6.0 l/min, cardiac index 2.9 l/min/m2 and pulmonary vascular resistance of 547 dynes. Pulmonary veno-occlusive disease (PVOD) was excluded in the patients on three grounds. Firstly, high resolution computer tomography showed no morphological changes typical for PVOD. Secondly, diffusion capacity of the lung for carbon monoxide (DLCO) values were greater than 50% predicted. Values around 50% are often seen in PVOD (Montani et al., 2008). Thirdly, patients II:4 and III:2 have received PAH medication for eight years and were stable under dual therapy. Whereas in PVOD a worsening of symptoms is often observed, once PAH medication has been given.
1mPAP ≥25 mmHg characterises pulmonary hypertension
2PAWP >15 mmHg together with mPAP ≥25 mmHg characterises post-capillary pulmonary hypertension due to left heart disease; PAWP ≤15 mmHg together with mPAP ≥25 mmHg characterizes pre-capillary PH
3sPAP >40 mmHg at rest and sPAP >45 mmHg at low workloads is considered here as abnotmal and exercise induced pulmonary hypertension, respectively (Nagel et al., 2015).
All living family members with manifest HPAH (II:4, III:2) carried a heterozygous mutations in BMPR2 and EIF2AK4. In contrast, two non-diseased family members (III:1 and III:4) carried only the BMPR2 mutation and no mutation in EIF2AK4. None of these family members developed manifest HPAH at of the time of this writing.
The first familial mutation lay within exon 12 of the BMPR2 gene (c.2308delC, p.(Arg770Glyfs*2)) and led to the deletion of a cytosine resulting presumably in a premature stop codon two amino acids downstream. The second mutation was located one base pair behind the end of exon 38 of the gene EIF2AK4 (c.4892+1G>T) resulting in the loss of the complete exon 38 (
While DNA was only available from five family members the pedigree analysis revealed two further obligate carriers of the BMPR2 mutation. The grandfather (I:1) and the aunt (II:2) of the index patient must have been carriers for the cousin (III:1) to harbour the mutation. At the same time, the EIF2AK4 mutation was most likely also present in the grandfather (I:1), who had died aged 49 years due to liver cirrhosis. Since the mother of the index patient (II:4) only developed manifest PAH at the age of 49 years, it is likely that the grandfather would have developed PAH due to the inferred presence of both mutations at a later stage in his life or had already developed the disease but had not been diagnosed until his death. Alternatively, the EIF2AK4 mutation might have arisen de novo in II:4 or as a genii line mosaicism in either grandparent of the index patient.
In HPAH we expect a BMPR2 mutation with a probability of 85% (Machado et al., 2015; Pfarr et al., 2011). Under the null hypothesis stating that the mutation in EIF2AK4 does not contribute to disease manifestation but instead represents a random event for the proband, the chance to observe the association of the two mutations has the probability of 0.00046. Taking the number of genes on the panel into account this association of both mutations under the null hypothesis reveals p=0.00046*30=0.014, which is significant below the 5% level. Hence, the co-occurrence of both mutations in affected family members is a significant association. Moreover, EIF2AK4 co-segregates with disease conditioned on all BMPR2 positive family members supporting the hypothesis of a second hit model, in which the diplotype of mutations in both genes has a high penetrance for PAH.
Members of a HPAH family were genetically and clinically assessed after providing their written informed consent for genetic and clinical analysis. The study was approved by the Ethics Committee at Heidelberg University and carried out in accordance with the Declaration of Helsinki (2013) of the World Medical Association. Diagnosis of PAH was continued by right heart catheterisation in all affected family members. Family members with no symptoms or signs of PAH were assessed by obtaining medical history, physical examination, 12-lead ECG, lung function test, chest X-ray, echocardiography at rest and during exercise and laboratory assessment as described previously (Ehlken et al., 2016).
DNA was extracted from peripheral blood using standardised procedures (Autogene Qiagen, Germany). Sanger sequencing using Big Dye Terminator V1.1 cycle sequencing kit and ABI 3130x1 genetic analyser and multiplex ligation-dependent probe amplification (MLPA, kit P093-C2, MRC-Holland, the Netherlands) was conducted for the index patient for the genes BMPR2 (ENSG00000204217) [SEQ ID NO. 3], ACVRL1 (ENSG00000139567) [SEQ ID NO. 1] and ENG (ENSG00000106991) [SEQ ID NO. 6].
Next-generation sequencing (NGS) was carried out to investigate potential mutations in PAH and candidate genes as described previously (Song et al., 2016). All known PAH genes (ACVRL1, BMPR1B, BMPR2, CAV1, EIF2AK4, ENG, KCNA5, KCNK3, SMAD1, SMAD4, SMAD9 and TOPBP1) and further candidate genes from the BMPR2 pathway and genes which were shown to have a PAH relevance in animal models such as KLF2, KLF4 and KLF5 were included in a PAH-specific gene panel. DNA was enriched with a customised SureDesign panel (Agilent Technologies), sequenced on the MiSeq and analysed with SeqPilot 4.1.2 as described previously (Song et al., 2016). Variants in exonic regions and exon-intron boundaries were characterised following the recommendations of the Human Genome Variation Society (HGVS, http://www.hgvs.org;version 2.15.11) (den Dunnen et al., 2016). Non-synonymous missense variants with a population frequency of less than 5% were assessed regarding their evolutionary conservation, location within functional gene domains and their functional consequence using four in silico prediction programmes: MutationTaster, SIFT, Align GVGD and PolyPhen2 implemented in Alamut Visual 2.7.1. Furthermore, in order to determine gene function, a systematic literature search was performed to investigate mutations, their functions within the cell and their involvement in the BMPR2 pathway, which is affected in most HPAH families (Machado et al., 2015). Any variants disrupting the function of a gene were considered mutations.
The COSMIC data base (Forbes et al., 2015) for somatic mutations and HGMD for germline mutations, were used respectively together with a systematic literature search in PubMed to list previously reported mutations. Cellular and molecular functions of affected genes relevant to phenotypes observed in PAH were also investigated by a broad literature search.
Potential mutations were confirmed with Sanger sequencing guaranteeing a 100% specificity. Family members of the index patient were assessed with Sanger sequencing to clarify mutation status.
Thirteen unrelated IPAH/HPAH patients without mutations in the genes BMPR2, ENG and ACVRL1 were screened for the presence of rare mutations using NGS assessing all exons and exon-intron boundaries. The Fisher's exact test was used to compare mutations in our sample to 126,216 controls (Lek et al., 2016) calculated with BIAS v.11.02.
Three family members of the HPAH family were diagnosed with invasively confirmed manifest PAH. The father (II:4) of the index patient (III:3) had died one year after diagnosis of severe and rapidly progressive HPAH and right heart failure aged 32 years. His two daughters (III:2 and III:3) were diagnosed with HPAH in 1993 and suffered from severe and rapidly progressive disease unresponsive to medical therapy (Table 8). They underwent lung and heart/lung transplantation, respectively, shortly after diagnosis both at the age of 25 years. Both of them are still alive and are doing well as of the time of this writing having been clinically followed for more than 20 years after transplantation. Neither of the sisters had any children. The brother (III:1) and further family members remained unaffected up to the present day with a clinical follow-up of >20 years as well.
In the genetic analysis of the two affected sisters, no disease-causing mutation, deletion or duplication was found in the known and previously published PAH genes (Table 9). By including new candidate genes in the NGS approach, we identified a new, germline heterozygous missense mutation in exon 2, c.862C>T p.H288Y in the Krüppel-like factor 2 (KLF2) gene on chromosome 19 (ENSG00000127528) [SEQ ID NO. 10] in both affected sisters (Table 9).
No DNA was available from the father who died early due to HPAH. Since the mutation was absent in the healthy mother (II:5) we infer its presence in the deceased father (II:4). We screened all first degree related family members of the father for the presence of the mutation in KLF2 with Sanger sequencing. The mutation was absent in all paternal siblings (II:1-II:3). None of them nor the grand-parents (I:1, I:2) of the index-patient developed PAH. This germline mutation was absent in exomes of >120,000 control subjects assessed by the Exome Aggregation Consortium and the genome Aggregation Database (Lek et al., 2016).
Similarly, KLF2 was entirely absent from the germline mutation data bases HGMD and ClinVar. The Fisher's exact test showed that the absence of the mutation in 126,216 controls compared to our sample ( 1/14, 2-sided p-value=0.0001) demonstrated a significant association of the KFL2 variant with PAH. The effect of the mutation was classified as pathogenic by four in silico prediction programmes (respective scores: MutationTaster: 1, SIFT: 0, PolyPhen2: 0.927, Align GVGD: C65). The mutation led to the substitution of a highly conserved nucleotide and subsequently the exchange of a highly conserved amino acid within a zinc finger protein domain. This domain is characterised by two cysteine and two histidine residues (2Cys-2His) forming two beta sheets and one alpha helix.
The mutation might have occurred de novo in the father, who could not be analysed, or was inherited by one of the grandparent presenting with reduced penetrance. Under both assumptions KLF2 co-segregates with the disease in this family based on the genetically analysed family members. So far we could not identify further KLF2 mutations in 13 other unrelated IPAH/HPAH patients without mutations in BMPR2, ENG or ACVRL1.
KLF2 is highly important for lung functioning, represented by its previous name “Lung KLF” and its high expression in the adult mouse lung (Anderson et al., 1995). We summarised the diverse array of cellular processes regulated by KLF2 such as cell differentiation, migration, coagulation and tissue development (Kumar et al., 2005), which are all involved in PAH pathogenesis. Studies implicated KLF2 as a key transcriptional regulator of endothelial pro-inflammatory activation (Bhattacharya et al., 2005; SenBanerjee et al., 2004). KLF2 also inhibited endothelial activation and proliferation (Bhattacharya et al., 2005) as well as the expression of endothelin-1, adrenomedullin and angiotensin converting enzyme, all of which increase vascular contractile tone (Dekker et al., 2005).
Mice with homozygous germline deletions of KLF2 die around day 14 during development due to heart failure preceded by a high cardiac output state (Lee et al., 2006). In contrast, heterozygous mice are viable and fertile (Yeo et al., 2014). KLF2 overexpression in a PH model of hypoxic rats was able to reduce right ventricular systolic pressure (RVSP) while its knock down increased RVSP and reduced the expression of the vasodilator endothelial nitric oxide synthase (eNOS) in normoxia (Dungey et al., 2011).
The features disclosed in the foregoing description, in the claims and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realizing the invention in diverse forms thereof.
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| Number | Date | Country | Kind |
|---|---|---|---|
| 16187084.5 | Sep 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/071886 | 8/31/2017 | WO | 00 |
