Genetics of suicide: a systematic review of twin studies.
OBJECTIVE
Convergent evidence from a multitude of research designs (adoption, family, genomescan, geographical, immigrant, molecular genetic, surname, and twin studies of suicide) suggests genetic contributions to suicide risk. The present account provides a comprehensive and up-to-date review of the twin studies on this topic.


METHODS
A total of 32 studies (19 case reports, 5 twin register-based studies, 4 population-based epidemiological studies, 4 studies of surviving co-twins) located through extensive literature search strategies are summarized and discussed here. This literature corpus was published between 1812 and 2006 in six languages and reports data from 13 countries.


RESULTS
A meta-analysis of all register-based studies and all case reports aggregated shows that concordance for completed suicide is significantly more frequent among monozygotic than dizygotic twin pairs. The results of co-twin studies rule out exclusively psychosocially based explanations of this pattern. Population-based epidemiological studies demonstrate a significant contribution of additive genetic factors (heritability estimates: 30-55%) to the broader phenotype of suicidal behavior (suicide thoughts, plans and attempts) that largely overlaps for different types of suicidal behavior and is largely independent of the inheritance of psychiatric disorders. Nonshared environmental effects (i.e. personal experiences) also contribute substantially to the risk of suicidal behavior, whereas effects of shared (family) environment do not.


CONCLUSIONS
The totality of evidence from twin studies of suicide strongly suggests genetic contributions to liability for suicidal behavior. To further research progress in this area, an extensive discussion of design limitations, shortcomings of the literature and further points is provided, including sources of bias, gaps in the literature, errors in previous reviews, age and sex effects and twin-singleton differences in suicide risk, and notes from a history-of-science view.
Voracek
Martin
M
Department of Basic Psychological Research, School of Psychology, University of Vienna, Vienna, Austria. martin.voracek@univie.ac.at
Loibl
Lisa Mariella
LM
D002423:Cause of Death; D004200:Diseases in Twins / Q000235:genetics* / Q000401:mortality / Q000523:psychology; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics*; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000235:genetics / Q000401:mortality / Q000523:psychology; D010641:Phenotype; D011159:Population Surveillance; D012307:Risk Factors; D012931:Social Environment; D013405:Suicide / Q000706:statistics & numerical data; D013406:Suicide, Attempted / Q000706:statistics & numerical data; D018433:Twin Studies as Topic; D014429:Twins, Dizygotic / Q000235:genetics / Q000523:psychology; D014430:Twins, Monozygotic / Q000235:genetics / Q000523:psychology