BACKGROUND: Population-based and family studies showed that impulsive-aggression predicts suicidality; however, the underlying etiological nature of this association is poorly understood. The objective was to determine the contribution of genes and environment to the association between childhood impulsive-aggression and serious suicidal ideation/attempt in young adulthood.
METHODS: N = 862 twins (435 families) from the Quebec Newborn Twin Study were followed up from birth to 20 years. Repeated measures of teacher-assessed impulsive-aggression were modeled using a genetically informed latent growth model including intercept and slope parameters reflecting individual differences in the baseline level (age 6 years) and in the change (increase/decrease) of impulsive-aggression during childhood (6 to 12 years), respectively. Lifetime suicidality (serious suicidal ideation/attempt) was self-reported at 20 years. Associations of impulsive-aggression intercept and slope with suicidality were decomposed into additive genetic (A) and unique environmental (E) components.
RESULTS: Additive genetic factors accounted for an important part of individual differences in impulsive-aggression intercept (A = 90%, E = 10%) and slope (A = 65%, E = 35%). Genetic (50%) and unique environmental (50%) factors equally contributed to suicidality. We found that 38% of the genetic factors accounting for suicidality were shared with those underlying impulsive-aggression slope, whereas 40% of the environmental factors accounting for suicidality were shared with those associated with impulsive-aggression intercept. The genetic correlation between impulsive-aggression slope and suicidality was 0.60, p = .027.
CONCLUSIONS: Genetic and unique environmental factors underlying suicidality significantly overlap with those underlying childhood impulsive-aggression. Future studies should identify putative genetic and environmental factors to inform prevention.