Objective: Several theoretical typology models have been proposed to classify alcoholism into more homogeneous subtypes using various criteria, for which age at onset of alcohol dependence is shared across many models. We investigated the evidence for the distinction between early- versus late-onset alcoholism by examining relevant phenotypic and genotypic variables.

Method: Data are from 1,248 individuals with alcohol dependence, who were interviewed to collect detailed clinical information. Early versus late onset of alcohol dependence was defined by the age at onset of 22 years. Odds ratio (OR) and Cohen's d were calculated as effect size for comparisons of clinical features between the two groups. We adjusted interviewed age and gender in logistic regression models. Case-control genetic analyses were conducted for the association between HTR1B, SLC6A4, DRD2, and OPRμ1 genes and subgroups of alcohol dependence using a sample of 530 controls screened for alcohol problems.

Results: Early-onset alcoholism exhibited significantly (p < .01) different clinical characteristics from late-onset alcoholism, including higher severity in alcohol dependence symptoms (d = 0.22) and maximum drinking quantity within 24 hours (d = 0.40), more rapid progression from regular drinking to meet alcohol dependence diagnosis (d = 1.73), higher expectancies for alcohol (d = 0.22–0.47), more comorbidity with externalizing disorders (ORs = 2.8–2.9), and greater prevalence of family alcohol use problems (d = 0.26–0.43). In addition, markers in the HTR1B and OPRμ1 genes showed genetic associations with subgroups of alcohol dependence (ORs = 1.5–2.4).

Conclusions: Our findings support that subgroups of alcohol dependence defined by onset age have phenotypic and genetic differences. The early-onset subgroup had more severe features for almost every aspect we examined. Coupled with genetic association findings, age at onset of alcohol dependence may serve as a simple but important clinical marker with implications for future etiological research and intervention.