ALCOHOL AND DRUG PROBLEMS - A MULTIVARIATE BEHAVIORAL GENETIC-ANALYSIS OF CO-MORBIDITY

Multivariate biometrical genetic analyses of self-report questionnaire items assessing problem alcohol and drug use were performed on data o btained from a sample of 438 volunteer twin pain (236 monozygotic twin pairs, 247 dizygotic twin pairs). Additive genetic influences were mo derate for all alcohol abuse items (21-46%), frequency of drug use (32 %) and illicit drug use (32%). Prescribed drug use and debilitating dr ug use were largely environmentally determined (86% and 94%, respectiv ely). The influence of environmental factors that influence all member s of a family to the same degrees (shared family environment) on each item was generally small (0-20%), whereas the influence of environment al factors unique to each family member (non-shared environment) compr ised over half of the total variance on all items. Genetic factor anal yses identified three uncorrelated common genetic factors. The first g enetic factor appears to represent problems associated with alcohol an d drug use, such as the inability to fulfil obligations at home, work or school. The second genetic factor is more specific to drug use and represents a general liability towards drug use, illicit or otherwise. The third genetic factor is specific to the alcohol use items only. T he observed co-morbidity of alcohol and drug misuse can be attributed largely to a non-shared environmental factor common to both domains. G enetic co-morbidity appears to be limited to alcohol and substance mis use behaviours that interfere with normal daily functioning.