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]. This evidence concerns the gene CX3CR1 and pulmonary arterial hypertension.