Interestingly, recent studies have potentially identified certain genetic risk factors for the development of depression in AD but not AD without depression including the tryptophan hydroxylase-1 (TPH1) A218C allele, monoamine oxidase A (MAOA) variable number tandem repeat (VNTR), and BDNF Val66Met allele [4]. The gene discussed is TPH1; the disease is depressive symptom measurement.