The MAO-A enzyme, which degrades 5-HT and other biogenic amines, could be contributing to the risk of AD in the Brazilian cohort (Nishimura et al., 2005), although a more recent study could not associate either the 5-HTTLPR genotype or a low-activity MAO-A variant with AD, but did observe an association between the 5-HTTLPR/MAO-A variants and a history of depression (Scholz et al., 2014). Here, MAOA is linked to Alzheimer disease.