Within-Family Transmission of Alcohol Use Disorder in Parent-Offspring, Sibling, and Cousin Pairs: A Contagion Model.

To determine whether alcohol use disorder (AUD) is transmitted within families as predicted by contagion, we examined parent-offspring, siblings, and cousin pairs ascertained from Swedish registries with a primary case with AUD. Our outcome variable was AUD registration in at-risk secondary cases. In offspring, risks for AUD registration in the 3 years after a parental index registration residing in the same household, neighborhood, or municipality increased by 1.6%, -0.5%, and 0.3%, respectively. For siblings of sibling index cases, parallel results were 3.2%, 1.2%, and 0.3%. For cousins of cousin index cases, no excess risk was seen for those residing in the same neighborhood or municipality. In siblings, AUD transmission was stronger in same versus opposite sex pairs and from older to younger versus younger to older siblings. These results support the hypothesis that AUD is transmitted among close family relationships and over limited geographical distances by a temporally dynamic contagion model.