FKBP5 and major depressive disorder: In a clinical study by Piechaczek et al. (2019) involving cases of major depression (n = 148) and a normal control group (n = 143), participants carrying at least one copy of the FKBP5 CATT haplotype or at least one minor allele of various FKBP5 SNPs had the highest risk of being in the major depression group.