Epidemiologic and molecular genetics of suicidal behavior

The current understanding of suicidal behaviors is that such behaviors are multidetermined and mental state and trait related. Genetic factors appear to be of great importance, as suggested by the findings of family, twin, and adoption studies. Whether these genetic factors are similar to those involved in the susceptibility to psychiatric disorders closely related to suicidal behavior (eg, manic depressive illness, schizophrenia or substance use disorders) is yet unknown. However, a genetic factor of susceptibility to suicide, independant or additive to the genetic transmission of the psychiatric disorders that are related to suicidal behavior, is strongly suggested by the data of the Copenhagen adoption study and a study of Amish families. Recently, new approaches have been proposed to identify the genetic component of such complex traits. Association studies between genetic markers and a disease phenotype has been suscessfully applied to several complex disease such as essential hypertension. One candidate gene for suicidal behaviors is the tryptophane hydroxylase (TPH) gene which is the first and possibly rate-limiting enzyme of the metabolic pathway for serotonin. Indeed, altered serotoninergic function in both completed suicide and suicide attempt has been one of the most replicated findings in modern biological psychiatry. In our knowledge, only two studies have tested the association between suicide attempt and the TPH gene and their authors found negative results. Despite these negative results, association studies that use candidate gene remain one of the methods of choice for studying the genetic component of suicidal behaviors.