REPLICATION OF THE STOCKHOLM ADOPTION STUDY OF ALCOHOLISM - CONFIRMATORY CROSS-FOSTERING ANALYSIS

Background: Two forms of alcoholism with distinct clinical features an d mode of inheritance were first distinguished in the Stockholm Adopti on Study. This involved a large sample of children born in Stockholm, Sweden, who were adopted at an early age and reared by nonrelatives. T ype 1 alcoholism had adult onset and rapid progression of dependence w ithout criminality, whereas type 2 had teenage onset of recurrent soci al and legal problems from alcohol abuse. Methods: A replication study was carried out with 577 men and 660 women born in Gothenburg, Sweden , and adopted at an early age by nonrelatives. The genetic and environ mental backgrounds of the adoptees were classified by the exact proced ures calibrated by discriminant analysis in the original study. Result s: Both type 2 and severe type 1 alcoholism were confirmed as independ ently heritable forms of alcoholism in male adoptees. The lifetime ris k of severe alcoholism was increased 4-fold in adopted men with both g enetic and environmental risk factors characteristic of type 1 alcohol ism compared with the others (11.4% vs 3.0%). Neither genetic nor envi ronmental risk factors for type 1 alcoholism by themselves were suffic ient to cause alcoholism. In contrast, the risk of type 2 alcoholism w as increased 6-fold in adopted sons with a type 2 genetic background c ompared with others, regardless of their postnatal environment (10.7% vs 2.0%). The sons with a type 2 genetic background in the replication sample had no excess of type 1 alcoholism, and vice versa, There was no increased risk of mild abuse in adopted men regardless of their gen etic or environmental background. Conclusion: Type 1 and type 2 alcoho lism are clinically distinct forms of alcoholism with causes that are independent but not mutually exclusive.