Clinically, polymorphisms in aromatase (CYP19A1), the enzyme that synthesizes oestrogen, are associated with higher oestrogen levels and an increased risk of PH development in female patients with advanced liver disease.4 In line with this, physiological concentrations of oestrogen mediate proliferation of human PASMCs and an inhibitor of endogenous oestrogen synthesis can reverse the development of PH in female rodents.5,6. The gene discussed is CYP19A1; the disease is liver disorder.