Familial transmission of externalizing syndromes in extended Swedish families.

Risk for criminal behavior (CB), alcohol use disorder (AUD), and drug abuse (DA) are known to be familial. We know less about their transmission across three generations. We examined 844,109 probands born in Sweden 1980-1990, their parents, aunts/uncles, and grandparents for registration in population-based registers for CB, AUD, and DA. Mean tetrachoric relative-proband correlations (95% CIs) were highest for DA (+0.24, 0.24-0.25), followed by CB (+0.23,0.22-0.23) and AUD (+0.17, 0.16-0.17). AUD and CB were relatively stably transmitted across generations, while DA resemblance among relatives was stronger in the younger generations. For all three syndromes, male-male transmission was modestly stronger than female-female. Cross-sex transmission was significantly weaker than same-sex transmission for DA and CB but not AUD. Risk to probands with only an affected grandparent or aunt/uncle were increased 50-60% for CB and AUD, and 70-100% for DA. Parallel figures for affected parents only and parents + grandparent or aunt/uncle were 2-3-fold and 4-5-fold for CB and AUD, and 4-5-fold and 6-7-fold for DA. CB, AUD, and DA are all substantially familial in the Swedish population with the transmission across three generations stable for CB and AUD but not DA. Modest quantitative sex effects are seen in the familial transmission of CB, AUD, and DA, and qualitative sex effects for CB and DA. Risk prediction in offspring is orderly with affection status in grandparental and avuncular relationships adding appreciably to that from the parental generation.