MTHFR and hyperhomocysteinemia: When stratified by MTHFR genotype, hyperhomocysteinemia was significantly associated with prevalent depressive disorder in the presence of C/T and T/T genotypes, and with incident and persistent depressive disorder in the presence of T/T genotype (positive predictive value and negative predictive values for incident depressive disorder was 39 and 96%, respectively; and for persistent depressive disorder was 78% and 73%, respectively).