Contribution of genes and environment to the longitudinal association between childhood impulsive-aggression and suicidality in adolescence

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.