Second, it is possible that the 22 patients with familial PAH excluded from analysis because they did not carry a detectable BMPR2 mutation do carry mutations in unexplored parts of the BMPR2 gene (or that they have inappropriately been categorized as having a familial disease but are in fact patients with IPAH). This evidence concerns the gene BMPR2 and idiopathic pulmonary arterial hypertension.