Chronic cigarette smoking has been linked to structural changes in several brain regions, including cerebellum33, and CYP2A6 variation mediates some functional brain changes in smokers34. These previous findings are consistent with the conclusion that brain nicotine or nicotine metabolite concentration can shape brain circuits, and raise the possibility that some of the toxicity they cause can be irreversible. Our observation of the association of the rs113288603 * T allele with age-related hearing loss symptoms and CYP2A6 expression in cerebellar hemisphere is consistent with and validated by these prior findings.
