Overlapping genetic and environmental influences on nonsuicidal self-injury and suicidal ideation: different outcomes, same etiology?
OBJECTIVE
Nonsuicidal self-injury (NSSI) and suicidal self-injury are very harmful behaviors and are associated with several psychiatric disorders. In the recently developed fifth edition of the DSM, NSSI and suicidal behavior disorder are for the first time introduced as conditions in their own right instead of symptoms of other psychiatric disorders. It is unclear to what extent NSSI and suicidal self-injury share the same underlying biological mechanisms and are influenced by the same environmental factors.


OBJECTIVE
To determine the relative importance of genetic and environmental influences on the variation in NSSI and suicidal ideation and their covariation.


METHODS
Classical twin design using a sample of 10,678 male and female adult twins (mean [SD] age, 32.76 [6.99] years) from the Australian Twin Registry, a population-based twin registry. Between 1996 and 2009, the twins participated in semistructured telephone interviews that primarily focused on psychiatric disorders.


METHODS
Lifetime presence of self-reported NSSI and suicidal ideation. RESULTS The prevalences of NSSI and suicidal ideation were 4.7% and 26.5%, respectively, and individuals who engaged in self-harm were much more likely to report suicidal ideation (odds ratio = 8.39; 95% CI, 6.84-10.29). Results from a bivariate genetic model indicated that genetic factors explain a substantial part of the variance in both NSSI (37% for men and 59% for women) and suicidal ideation (41% for men and 55% for women), while residual influences (including nonshared environmental influences and measurement error) explain the remainder of the variance. Shared (family) environment did not seem to play a role. Moreover, both behaviors were strongly correlated (r = 0.49 for men and 0.61 for women), and this correlation was largely explained by overlapping genetic influences (76% for men and 62% for women), whereas residual influences accounted for the remainder of the phenotypic correlation.


CONCLUSIONS
Results indicated that the substantial correlation between NSSI and suicidal ideation is largely driven by overlapping genetic factors, suggesting that the 2 behaviors share similar biological underpinnings. Overlapping residual influences also explain part of the covariance between the 2 traits. Future research should further investigate which genetic and environmental influences underlie the vulnerability to NSSI and suicidal ideation.
Department of Developmental Psychology and EMGO Institute for Health and Care Research, VU University, Amsterdam, the Netherlands.
Dominique F
DF
Maciejewski
Department of Developmental Psychology and EMGO Institute for Health and Care Research, VU University, Amsterdam, the Netherlands.
Hanneke E
HE
Creemers
Addictions Department, Institute of Psychiatry, King's College London, London, England.
Michael T
MT
Lynskey
Department of Psychiatry, Washington University School of Medicine, St Louis, Missouri.
Pamela A F
PA
Madden
Department of Psychiatry, Washington University School of Medicine, St Louis, Missouri.
Andrew C
AC
Heath
Faculty of Arts and Social Sciences, University of the Sunshine Coast, Sippy Downs, Australia.
Dixie J
DJ
Statham
Genetic Epidemiology, QIMR Berghofer Medical Research Institute, Brisbane, Australia.
Nicholas G
NG
Martin
Department of Developmental Psychology and EMGO Institute for Health and Care Research, VU University, Amsterdam, the Netherlands.
Karin J H
KJ
Verweij
D000328:Adult; D000368:Aged; D001315:Australia; D004777:Environment; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008957:Models, Genetic; D012042:Registries; D057566:Self Report; D016728:Self-Injurious Behavior / Q000209:etiology* / Q000235:genetics* / Q000523:psychology; D012737:Sex Factors; D059020:Suicidal Ideation