This invention provides: methods of determining a predisposition or susceptibility of a subject to a mood disorder, a schizophrenia, or a neuro-psychiatric disease or disorder, comprising detecting a presence of a polymorphism in a vesicular monoamine transporter 1 (VMAT1) gene or a haplotype comprising the polymorphism, and methods of treating a mood disorder, a schizophrenia, or a neuro-psychiatric disease or disorder in a subject, comprising contacting the subject with a composition that encodes a VMAT protein or modulates an expression or activity of same.