Clinical Relevance

Several lines of evidence, coming from studies of family history of suicide and more definitively from twin and adoption studies, suggest that suicidal behavior has a genetic component partly independent from the familial transmission of major psychiatric disorders (Garfinkel et al. 1982; Pfeffer et al. 1994; Roy et al. 1997). This is supported by clinical data. In fact, about 10% of those who commit or attempt suicide have no identifiable psychiatric illness (Oquendo et al. 2008). It is proposed that suicidal behavior could be considered a separate diagnostic category documented on a sixth axis as part of the newer classification of mental diseases within the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-V) (Oquendo et al. 2008). This is because suicidal behavior meets the criteria for diagnostic validity set forth by Robins and Guze (1970), and it does so to the same extent as most conditions treated by clinicians. In fact, such behavior is described so well clinically that research has pointed towards postmortem and in vivo laboratory markers (Mann 2003; Posner et al. 2007).

It is now possible to perform a strict differential diagnosis for suicidal behavior, and recent data from follow-up studies confirm higher rates in those with a previous diagnosis of psychiatric illness and a family history of suicidal behavior (Posner et al. 2007; Oquendo et al. 2006; Brent et al. 2002). Voracek and Loibl (2007) showed that the heritability of suicidal behavior as a broader phenotype (attempts, thoughts, and plans) is between 30% and 55%. Data from twin studies (Roy 1993; Statham et al. 1998) strongly supports the role of a genetic component in suicidal behavior, specifically, suicide attempts and completion.

Independently transmitted factors may partly explain the genetic risks for major depression (Gershon 1990) and for suicide (Roy 1993; Roy et al. 1995). Adoption studies rule out effects of a shared environment that may influence results of twin studies and indicate that genetic transmission of suicide risk is independent from transmission of major psychiatric disorders such as mood disorders or schizophrenia.

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