Bone morphogenetic protein receptor-II mutation Arg491Trp causes malignant phenotype of familial primary pulmonary hypertension

The features of rare pathogenic BMPR2 variants in pulmonary arterial hypertension: Comparison between patients and reference population

BACKGROUND

Mutations in the gene encoding bone morphogenetic protein receptor type 2 (BMPR2) are the most common genetic risk factors underlying pulmonary arterial hypertension (PAH). However, the features of PAH-related BMPR2 rare variants remain unclear. We propose that the discrepancy of BMPR2 rare variants landscape between patients with PAH and reference population would be important to address the genetic background of PAH-related variants.

METHODS

We genotyped BMPR2 rare variants in 670 Chinese patients with pulmonary arterial hypertension. The BMPR2 rare variants were screened in 10,508 reference people from two exome databases.

RESULTS

The prevalence of rare BMPR2 variants in patients with PAH was significantly higher compared to the reference population (21.5%, 144/670 vs 0.87%, 91/10508, p = 1.3 × 10^-118). In patients with PAH, 49% of identified BMPR2 rare variants were loss-of-function or splicing. These BMPR2 rare variants were only observed in 1% of the reference population (p = 9.0 × 10^-12). Arg491, which is absent in the reference population, represented as hot-spot site (14.6%, 21/144) in PAH patients. BMPR2 missense mutations in PAH patients were more likely distributed in extracellular ligand-binding domain (ECD, 29.7% vs 11.1%, p < 0.001). Compared with Non-PAH-related variations, PAH-related missense variants tend to alter the amino acid electric status (51.4% vs 23.3%, p < 0.001).

CONCLUSIONS

BMPR2 variants located in extracellular ligand-binding domain or altered the amino acid electric status are more pathogenic.

The specialty of pulmonary vascular medicine in China: historical development and future directions

Over the past 40 years, Chinese experts have made great progress on research, diagnosis, and therapy of pulmonary vascular disease, including pulmonary embolism and pulmonary hypertension. These theoretical and clinical advances have increased public awareness about this group of conditions, which are associated with significant morbidity and mortality in China and worldwide. With its theoretical basis combining knowledge from cardiovascular and pulmonary medicine, pulmonary vascular disease has developed into a separate, unique specialty in hospitals across China and worldwide. This article will provide a short historical perspective but also an outlook into the future of this exciting novel discipline. We provide a Chinese perspective, based on our research and clinic experience over the past decades.

Novel promoter and exon mutations of the BMPR2 gene in Chinese patients with pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH), which is clinically characterized by a sustained elevation in mean pulmonary artery pressure leading to significant morbidity and mortality, is caused by intense remodeling of small pulmonary arteries by endothelial and smooth muscle proliferation. Genetic studies in familial PAH (FPAH) have revealed heterozygous germline mutations in the bone morphogenetic protein type II receptor (BMPR2), a receptor for the transforming growth factor (TGF)-beta/BMP superfamily. In this study, we conducted mutation screening in the promoter region and the entire coding regions as well as the intron/exon boundaries of the BMPR2 gene in 20 Chinese patients with either idiopathic or FPAH. All novel detected mutations were excluded by their presence in a panel of 200 chromosomes from normal individuals. A novel mutation, G-669A, in the promoter sequence of the BMPR2 gene was identified in one patient with FPAH, and no exonic mutations were detected in the proband. This mutation abolished a potential specificity protein 3 (sp3) transcription factor-binding site, and a dual luciferase assay showed that the promoter carrying the -669A allele had significantly decreased transcriptional activity compared with -669G allele. Of the other 19 patients, three novel heterozygous exonic mutations were identified: a frame shift mutation with deletion of TG at the nucleotide position 608-609 in exon 5 (Leu203fsX15), a nonsense mutation at the nucleotide position 292 in exon 3 (Glu98X) and a missense single nucleotide substitution in exon 12 (Ser863Asn).

Registry and Survival Study in Chinese Patients With Idiopathic and Familial Pulmonary Arterial Hypertension

BACKGROUND

To evaluate the clinical features and survival data of patients with idiopathic pulmonary arterial hypertension (PAH) and familial PAH in Chinese patients.

METHODS

Seventy-two patients with idiopathic PAH and familial PAH were enrolled in the study from 1999 to 2004 and were classified into two groups according to World Health Organization (WHO) functional class (I/II and III/IV). Clinical and hemodynamic data were recorded.

RESULTS

The mean age of the 72 patients was 35.9 years with female patient/male patient ratio of 2.4:1. A significant difference was identified in the clinical presentation between two WHO functional class groups at baseline. Echocardiography showed a mean pulmonary systolic pressure of 98 mm Hg. Left ventricular end-diastolic diameter was significantly smaller in the group of patients in WHO functional class III/IV than in those in class I/II group. After follow-up for a mean (+/- SD) duration of 40.1 +/- 20.0 months, the survival rates at 1, 2, 3, and 5 years were 68.0%, 56.9%, 38.9%, and 20.8%, respectively. A significant difference was identified in survival rate between the class I/II and class III/IV groups (p = 0.02 [log rank test]).

CONCLUSIONS

The baseline characteristics and survival rates of our cohort study are close to those of the National Institutes of Health Registry in the 1980s, and the 1-year survival rate is obviously lower for patients in this registry than for those in the French registry between 2002 to 2003. Lack of effective treatment was the main cause of poor survival in this study. Our results support the need of an appropriate treatment strategy for this devastating disease in China.

Mutations of the TGF-beta type II receptor BMPR2 in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is clinically characterized by a sustained elevation in mean pulmonary artery pressure leading to significant morbidity and mortality. The disorder is typically sporadic, and in such cases the term idiopathic PAH (IPAH) is used. However, cases that occur within families (familial PAH (FPAH)) display similar clinical and histopathological features, suggesting a common etiology. Heterozygous mutations of a type II member of the TGF-beta cell signaling superfamily known as BMPR2 on chromosome 2q33 have been identified in many kindreds with FPAH, yet display both reduced penetrance and sex bias. This report presents the compilation of data for 144 distinct mutations that alter the coding sequence of the BMPR2 gene identified in 210 independent PAH subjects. This large data set characterizes the extent of sequence variation and reveals that the majority (71%) of mutations in FPAH and IPAH comprise nonsense, frameshift, and splice-site defects, and gene rearrangements. These predict premature termination of the transcript with likely loss through the process of nonsense-mediated decay (NMD). A total of 44 missense mutations were identified that substitute amino acid residues at highly conserved sites within recognized functional domains of the mature receptor. We assess this category of mutations in the context of their heterogeneous effects on cell signaling when assayed by in vitro cell-based systems. Disease-causing mutation hot-spots within BMPR2 are summarized. Taken together, these observations are likely to aid in the development of targeted mutation detection strategies relevant for patient management. Finally, we examine the age- and sex-dependent reduced penetrance of BMPR2 mutations by reviewing bmpr2 animal models and the requirement for additional genetic and/or environmental modifiers of disease. In conclusion, these data provide compelling genetic evidence that haploinsufficiency is the predominant molecular mechanism underlying disease predisposition, and support the concept of a critical threshold of signaling activity below which disease may be precipitated.

Gross BMPR2 gene rearrangements constitute a new cause for primary pulmonary hypertension

PURPOSE

Approximately 50% of patients with familial primary pulmonary hypertension (FPPH) have been reported to have mutations within the bone morphogenic protein receptor type 2 (BMPR2) gene. The vast majority of these mutations were identified by PCR amplification and sequencing of individual exons. The aim of our study was to determine if additional BMPR2 mutations not found by exon sequencing alone could account for a significant portion of these negative cases.

METHODS

We examined DNA samples from 12 families, previously found to be negative for BMPR2 mutations, to identify any large BMPR2 gene rearrangements.

RESULTS

Southern blot analysis found large gene rearrangements in four (33%) unrelated kindreds. Further analysis by reverse transcriptase PCR (RT-PCR) of BMPR2 transcripts from two of these kindreds found one to be heterozygous for a exon 10 duplication and the second to be heterozygous for a deletion of exons 4 to 5. Nonhomologous recombination is believed to be the cause of these large insertions/deletions.

CONCLUSION

Our results demonstrate the inherent problems associated with exon-by-exon sequencing and the importance of other screening methods such as Southern blot and RT-PCR in the identification of BMPR2 mutations.