A study, investigating three CYP1A2 polymorphisms, found that the coffee-PD association was the strongest among subjects homozygous for either variant allele c.-164A>C (p for interaction = 0.05) or c.1545T>C (p for interaction = 0.04) (i.e., slow metabolizers of caffeine) [56]. The gene discussed is CYP1A2; the disease is Parkinson disease.