The molecular cloning and characterisation of the gene mutated in primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a frequently lethal disease, of unknown aetiology. The disorder is characterised by an obliteration of small pulmonary arteries that generates a sustained elevation of pulmonary vascular resistance, leading to progressive right-heart failure. Among the estimated 6-10 % of cases with a family history of disease, the PPH gene segregates in an autosomal dominant manner and acts with substantially reduced penetrance. A positional cloning strategy was employed to isolate the causative gene. Initially, novel recombination events were identified in affected individuals from two PPH kindreds, to significantly reduce the previously established linkage interval, at chromosome 2q31-33, from 25 cM to 4.8 cM. A complete physical map, comprised of large-insert cloning vectors, was constructed across the new genetic interval, in combination with a comprehensive transcript map. Sequence analysis of six positional candidates led to the discovery of mutation, confined to PPH patients and gene carriers, in the BMPR2 gene, encoding the bone morphogenetic protein receptor type II, a member of the TGF-p superfamily. Further analysis of BMPR2 in a cohort of 55 PPH families and 50 sporadic patients revealed diverse pathogenic mutation in 50% and 32% of cases respectively. These data identified a common genetic mechanism, molecular haploinsufficiency, underlying most cases with the disease. An additional set of six families in which both pulmonary hypertension and the autosomal dominant disorder hereditary haemorrhagic telangiectasia (HHT), were observed to co-segregate were investigated. The detection of novel mutation, of the TGF-P type I receptor ALK1, in 5 of the 6 families emphasised the importance of TGF-P signalling in vascular stability of the pulmonary circulation. In conclusion, this study confirms that genetic abnormalities in either of the intracellular signalling receptors, ALK1 or BMPR-II, are critical elements in the pathogenesis of pulmonary hypertension.