Specifically, compared to healthy controls, individuals with idiopathic postpartum mood disorders and relevant animal models may display (a) an elevated ratio of sulfated to free circulating steroids including allopregnanolone, pregnenolone, and cholesterol; (b) genetic association with, and altered expression/activity of, steroid-modulating, extracellular matrix, and signalling molecules (e.g. STS, STOML3, CCN2, CCN3, ADCY8, ARHGDIG, HMCN1, TRPM3, and PDE10A); and (c) evidence for dysregulation of calcium signalling. The gene discussed is ARHGDIG; the disease is mood disorder.