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

A method for treating a human subject with depression, the method comprising:

• assaying a biological sample from said human subject who has been diagnosed with depression, and detecting in the biological sample a combination of the following single nucleotide polymorphisms (SNPs):
• (i) a SNP at position 677 of SEQ ID NO. 1 or position 27 of SEQ ID NO. 7 (rs1801133) comprising at least one thymine “T” allele, wherein the SEQ ID NO. 1 and SEQ ID NO. 7 are each independently a portion of a genomic nucleic acid sequence of methylenetetrahydrofolate reductase (MTIWR);
• and
• (ii) a SNP at position 2756 of SEQ ID NO. 2 or position 27 of SEQ ID NO. 9 (rs1805087) comprising at least one guanine “G” allele, wherein 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), which human subject has an increased likelihood of response to a treatment;
• administering said treatment comprising a composition comprising an effective amount of a folate-containing compound, wherein said folate containing compound is at least 15 mg/day of 6-(S) 5-methyltetrahydrofolate, together with an antidepressant drug, wherein the antidepressant drug is a selective serotonin reuptake inhibitor, to the human subject to treat depression.