Although PAH is known to correlate with various genetic and environmental factors, including mutations in the BMPR2 gene, the presence of pre-existing connect tissue diseases (SLE, rheumatoid arthritis, systemic sclerosis, etc.), HIV/schistosomiasis infection, and others [148], the majority of PAH cases are idiopathic (occur without a known cause) [149]. The gene discussed is BMPR2; the disease is pulmonary arterial hypertension.