This study has two hypotheses: (1) premenopausal women who suffer from MDD and are being treated with SSRI treatment exhibit lower BMD when compared to healthy controls; (2) premenopausal women who are diagnosed with MDD and are being treated with SSRI treatment exhibit evidence of lower bone formation (i.e., P1NP) but higher bone metabolism markers (i.e., RANKL, OPG and RANKL/OPG ratio). The gene discussed is TNFRSF11B; the disease is major depressive disorder.