The Sources of Parent-Child Transmission of Risk for Suicide Attempt and Deaths by Suicide in Swedish National Samples

OBJECTIVE: The authors aimed to clarify the sources of parent-child transmission for suicide attempt and death by suicide. METHODS: Three sources of parent-child resemblance (genes plus rearing, genes only, and rearing only) were examined in parents and offspring from four family types from Swedish national samples: intact nuclear families, families with a not-lived-with biological father, families with a stepfather, and adoptees and their biological and adoptive parents. Parent-child resemblance was assessed primarily by tetrachoric correlation. RESULTS: For suicide attempt to suicide attempt transmission, best-estimate tetrachoric correlations for genes plus rearing, genes only, and rearing only 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. Suicide attempt was more strongly transmitted to male offspring compared with female offspring. Parental psychiatric disorders accounted for 40% of the genetic transmission but had no impact on rearing effects. For suicide death to suicide death 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 -0.05 (95% CI=-0.17, 0.07), respectively. Although the suicide attempt-suicide death genetic correlation was high (0.84), the hypothesis that they reflect behaviors only differing in severity on the same continuum of genetic liability could be rejected. CONCLUSIONS: The transmission of suicide attempt across generations is moderately strong and arises equally from genetic and rearing effects. Parental psychiatric illness explains almost half of the genetic transmission of suicide attempt but none of the rearing effect. Suicide death is modestly transmitted across generations, probably via genetic effects, although rearing may play a role. While suicide attempt and suicide death share a substantial proportion of their hereditary risk, they do not, from a genetic perspective, simply reflect milder and more severe forms of the same diathesis.