- The frequency of several gene polymorphisms that are implicated in stress and affective disorder, including 5HTTLPR S/S (serotonin receptor), COMT (catechol-o-methyltransferase enzyme), Val/Met BDNF (brain-derived neurotrophic factor) and FKBP5 rs1360780 genotypes, as well as other polymorphisms or mutations to be determined later.