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

The present invention provides assays, methods and compositions for selecting a treatment regimen for a patient having depression or at risk for depression and/or treating at least one symptom of depression in the subject, based on the recognition that specific combinations of single nucleotide polymorphisms (SNPs) are associated with a therapeutic response to a folate-comprising compound. Provided herein are also methods for improving the effectiveness of an antidepressant drug administered to a subject with depression or at risk for depression by administering an adjunctive therapy of a folate-comprising compound to the subject if the subject carries a specific combination of SNPs that are predictive of a therapeutic response. Furthermore, provided herein are compositions of the folate-comprising compound.