Assays and methods for selecting a treatment regimen for a subject with depression

An assay for selecting a treatment regimen for a human subject with depression, comprising (a) subjecting a test sample previously obtained from a human subject, who is diagnosed as having depression or having a risk for depression, to at least one genotyping assay adapted to determine the genotypes of at least two loci. The at least two loci are: i. position 677 of SEQ ID NO. 1 or position 27 of SEQ ID NO. 7 (identified by rs1801133), where the SEQ ID NO. 1 and SEQ ID NO. 7 are each independently a portion of a genomic nucleic acid sequence of methylenetetrahydrofolate reductase (MTHFR) or ii.position 2756 of SEQ ID NO. 2 or position 27 of SEQ ID NO. 9 (identified by rs1805087), where the SEQ ID NO. 2 and SEQ ID NO. 9 are each independently a portion of a genomic nucleic acid sequence of methionine synthase (MTR). The assay furhter includes b) detecting from the genotypes of said at least two loci the presence of a single nucleotide polymorphism (SNP) selected from the following: i. a SNP677 at position 677 of SEQ ID NO. 1 or position 27 of SEQ ID NO. 7 comprising at least one thymine "T" allele; ii. a SNP2756 at position 2756 of SEQ ID NO.2 or position 27 of SEQ ID NO. 9 comprising at least one guanine "G" allele; and iii. a combination of at least one SNP677 T allele and at least one SNP2756 G allele; and if at least one of T allele at position SNP677 or at least one G allele at position SNP2756 or both at least one T allele at position SNP677 and at least one G allele at position SNP2756 is detected, then selecting a treatment regimen comprising an effective amount of a folate-containing compound.