CYP1B1 and pulmonary arterial hypertension: CYP1B1, whichhydroxylates estrogen at the C4 and, to a lesser degree, C2 and C16 positions, isof particular interest as it is highly expressed in PASMCs isolated from PAHpatients [80], and genetic polymorphisms affecting CYP1B1 protein function havebeen associated with decreased ratios of “good” 2-estrogens metabolite to“bad” 16-estrogen metabolites as well as PAH penetrance in females withBMPR2 mutations [81].