Parental psychiatric illness linked to 40% of genetic transmission of suicide attempt
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Parental psychiatric illness was associated with suicide attempts among offspring, according to study results published in American Journal of Psychiatry.
“Psychiatry has long been interested in the familial transmission of suicidal behavior,” Kenneth S. Kendler, MD, of the Virginia Institute for Psychiatric and Behavioral Genetics and department of psychiatry at Virginia Commonwealth University, and colleagues wrote. “Despite a substantial number of family and twin studies of both suicide attempt and death by suicide that have confirmed important familial and genetic contributions, we are aware of only two previous adoption studies specifically focused on death by suicide and only one focusing on suicide attempt.”
One of these studies examined only aggregated data and adoptive relatives of adoptees who died by suicide, and the other examined biological and adoptive siblings of adoptees who died by suicide or had suicide attempt history, respectively. To the researchers’ knowledge, no study had yet looked at rates of suicidal behaviors among offspring of adoptive and biological parents who had a history of suicide attempt and/or died by suicide.
In the current study, Kendler and colleagues sought to evaluate the sources of cross-generational transmission of suicide death and attempt. Specifically, they examined three sources of parent-child resemblance, which were genes plus rearing, genes only and rearing only. They obtained data from Swedish national samples from four family types, which were intact nuclear families, families with a not-lived-with biological father, families with a stepfather and adoptees and their adoptive and biological parents. Further, they used tetrachoric correlation to assess parent-child resemblance.
Genes plus rearing, genes only and rearing only best-estimate tetrachoric correlations were 0.23 (95% CI, 0.23-0.24), 0.13 (95% CI, 0.11-0.15) and 0.14 (95% CI, 0.11-0.16), respectively, for suicide attempt to suicide attempt transmission. Male offspring were more likely to exhibit suicide attempt transmissions than female offspring. Parental psychiatric disorders had no impact on rearing effects; however, they accounted for 40% of the genetic transmission. Best estimates of tetrachoric correlations for genes plus rearing, genes only and rearing only were 0.16 (95% CI, 0.15-0.18), 0.07 (95% CI, 0.02-0.12) and 20.05 (95% CI, 20.17-0.07), respectively, for suicide death to suicide death transmission.
“Suicide attempt is strongly transmitted from parents to their children, and this transmission arises nearly equally from genetic and rearing effects,” the researchers wrote. “While parental psychiatric and substance use disorders can explain almost half of the genetic transmission of suicide attempt across generations, these disorders had no effect on the impact of being reared by a nonbiological parent with a history of suicide attempt.
“Suicide death is modestly transmitted across generations, with genetic effects likely being more important than rearing effects,” they added. “While suicide attempt and suicide death are substantially genetically correlated, a model that proposes that they reflect quantitatively different degrees of severity on the same continuum of liability can be ruled out.”