Genetic origins of the association between verbal ability and alcohol dependence symptoms in young adulthood

Background. Cognitive deficits in alcohol dependence (AD) have been observed, poorer verbal ability being among the most consistent findings. Genetic factors influence both cognitive ability and AD, but whether these influences overlap is not known. Method. A subset of 602 monozygotic (MZ) and dizygotic (DZ) twins from FinnTwin16, a population-based study of Finnish twins, was used to study the associations of verbal ability with DSM-III-R diagnosis and symptoms of AD, the maximum number of drinks consumed in a 24-h period, and the Rutgers Alcohol Problem Index (RAPI) scores. These twins, most of them selected for within-pair discordance or concordance for their RAPT scores at age 18.5 years, were studied with neuropsychological tests and interviewed with the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA) in young adulthood (mean age 26.2 years, range 23-30 years). Results. All alcohol problem measures were associated with lower scores on the Vocabulary subtest of the Wechsler Adult Intelligence Scale - Revised (WAIS-R), a measure of verbal ability. In bivariate genetic models, Vocabulary and the alcohol problem measures had moderate heritabilities (0.54-0.72), and their covariation could be explained by correlated genetic influences (genetic correlations -0.20 to -0.31). Conclusions. Poorer verbal ability and AD have partly overlapping biological etiology. The genetic and environmental influences on the development of cognitive abilities, alcohol problems and risk factors for AD should be studied further with prospective longitudinal designs.