As examples, recent ambient PM2.5 levels were associated with lower DNA methylation of the proinflammatory gene inducible nitric oxide synthase (iNOS encoded by NOS2A) [20], and chronic exposure to PAH was associated with methylation of the asthma regulatory gene Forkhead box transcription factor 3 (FOXP3) [21]. The gene discussed is NOS2; the disease is asthma.