As with many diseases, there can be genetic predispositions for certain disease due to the presence of mutations. Pulmonary hypertension is no exception and research has demonstrated that mutations in the BMPR2 gene causes pulmonary arterial hypertension. It is believed that a mutation in BMPR2 actually promotes cell division (proliferation) or you prevents cell death. The result of this is an overgrowth of cells in the small arteries of the lungs. This in turn causes a narrowing of the vessel lumen effectively decreasing its diameter which increases resistance to blood flow. A larger diameter blood vessel has less resistance to flow. Blood pressure in the heart (right ventricle) and pulmonary artery increases to accommodate the increased resistance to flow. Research is currently underway to determine if other genes and possibly environmental factors might be involved as well.
It is known that BMPR2 is inherited in an autosomal dominant pattern. This means that each cell that expresses this gene has one copy of a mutated BMPR2 gene meaning you still have one good allele. People have two copies of a gene: one you got from your mother and one you got from your father. With one bad copy, this presents with predisposition. In other words, people need to come in contact with something that causes the good allele to mutate. This is what leads to contracting the disease. It has been reported that many individuals with a mutated BMPR2 gene never present with PAH. Nevertheless, the mutated gene will be passed down from generation to generation.