[Biological review of completed suicide]

Family, twin and adoption studies have revealed genetic factors involved in suicide, while the accumulation of stress and mental illnesses are major contributing factors of suicide. Since higher lethality of suicidal behavior is considered to increase familial liability to suicidal behavior, we believe biological research of completed suicide is most important for a better understanding of the pathophysiology in suicide. Dysregulated hypothalamic-pituitary-adrenal axis has gained a special interest in the neurobiology of suicide, mostly because of the findings using a dexamethasone suppression test (DST), in which DST non-suppressors show a nearly 10-fold higher risk of completed suicide than DST suppressors in a depressed cohort. Other data mainly from postmortem brain studies indicate abnormalities of the noradrenergic-locus coeruleus system, serotonergic system, endogenous opioid system, brain-derived neurotrophic factor, inflammatory cytokines and omega-3 fatty acid in completed suicide. However, genetic research of complete suicide is behind other mental problems because it is extremely difficult to obtain tissue samples of completed suicide. Under the difficult situation, we now retain over 800 blood samples of suicide completers thanks to bereaved families' cooperation. We are actively working on the research of suicide, for instance, by performing a GWAS using 500 samples of suicide completers.