Recent studies suggest that the effects of some genetic variants related to asthma, located on glutathione S-transferase (GST), methylenetetrahydrofolate reductase (MTHFR), gasdermin-like (GSDML) and ORMDL3 genes, are modified by environmental exposures, including tobacco smoke exposure [116, 162–167]. The gene discussed is MTHFR; the disease is asthma.