The aims of the present study are to identify alcohol use disorder (AUD) classes among a population-based Swedish sample, determine if these classes differ by variables known to be associated with AUD and determine whether some AUD classes have stronger genetic influences than others.
A latent class analysis (LCA), based on types of registrations, was conducted on Swedish individuals with an AUD registration born between 1960 and 1990 (N = 184,770). These classes were then validated using demographics; patterns of comorbidity with drug abuse, psychiatric disorders and criminal behavior; and neighborhood-level factors, i.e. peer AUD and neighborhood deprivation. The degree of genetic and environmental influence was also investigated.
The best-fit LCA had four classes: (a) outpatient/prescription, characterized by a mix of outpatient medical and prescription registrations, (b) low-frequency inpatient, characterized entirely by inpatient medical registrations, with the majority of individuals having one AUD registration, (c) high-frequency mixed, characterized by a mix of all four registration types, with the majority having four or more registrations and (d) crime, characterized almost entirely by criminal registrations. The highest heritability for both males and females was found for Class 3 (61% and 65%, respectively) and the lowest for Class 1 (20% for both), with shared environmental influences accounting for 10% or less of the variance in all Classes.
Using comprehensive, nationwide registry data, we showed evidence for four distinct, meaningful classes of AUD with varying degrees of heritability.
BACKGROUND: Two forms of alcoholism with distinct clinical features and mode of inheritance were first distinguished in the Stockholm Adoption Study. This involved a large sample of children born in Stockholm, Sweden, who were adopted at an early age and reared by nonrelatives. Type 1 alcoholism had adult onset and rapid progression of dependence without criminality, whereas type 2 had teenage onset of recurrent social 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 environmental backgrounds of the adoptees were classified by the exact procedures calibrated by discriminant analysis in the original study. RESULTS: Both type 2 and severe type 1 alcoholism were confirmed as independently heritable forms of alcoholism in male adoptees. The lifetime risk of severe alcoholism was increased 4-fold in adopted men with both genetic and environmental risk factors characteristic of type 1 alcoholism compared with the others (11.4% vs 3.0%). Neither genetic nor environmental risk factors for type 1 alcoholism by themselves were sufficient to cause alcoholism. In contrast, the risk of type 2 alcoholism was increased 6-fold in adopted sons with a type 2 genetic background compared 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 genetic or environmental background. CONCLUSION: Type 1 and type 2 alcoholism are clinically distinct forms of alcoholism with causes that are independent but not mutually exclusive.