DNA hyper-methylation has been observed in promoters already described as deregulated in PAH pathogenesis including the fibroblast growth factor (FGF) family, the receptor of the inflammatory chemokine fractalkine (CX3CR1) and the tumor necrosis factor family (TNFSF4, alias OX40L) [13]. The gene discussed is TNFSF4; the disease is pulmonary arterial hypertension.