While there have been mixed results about oxytocin levels in depression, certain oxytocin receptor single nucleotide polymorphisms (SNPs) have been associated with unipolar depression (Costa et al., 2009) and could be a mediator of selective serotonin reuptake inhibitor (SSRI) response (Uvnäs-Moberg et al., 1999). The gene discussed is OXTR; the disease is major depressive disorder.