Given that the APOE ε4 allele has been linked to AD in a Brazilian cohort via co-segregation with a MAO-A polymorphism and an allelic variant of the serotonin transporter (Nishimura et al., 2005) and that a multiplex protein biochip for screening for AD –based on the ε4 allele and MAO-B– has been proposed (Veitinger et al., 2014), there is surprisingly very little published on the interaction between APOE risk alleles and MAO. Here, APOE is linked to Alzheimer disease.