Particulate matter with an aerodynamic diameter of <2.5 μm (PM2.5) exacerbates asthma symptoms [84], and a recent genome-wide study demonstrated that the effects of acute PM2.5 exposure are associated with changes in CysLT1 expression and methylation of CpG sites on the CysLT1 and LTC4S genes [85]. This evidence concerns the gene CYSLTR1 and asthma.