Genetic and environmental influences on posttraumatic stress disorder, alcohol and drug dependence in twin pairs

We investigated whether and to what degree genetic and environmental contri butions overlap among posttraumatic stress disorder (PTSD), alcohol depende nce (AD) and drug dependence (DD). Subjects were 3304 monozygotic and dizyg otic male-male twin pair members of the Vietnam Era Twin Registry who parti cipated in 1992 telephone administration of the Diagnostic Interview Schedu le Version 3 Revised (DIS-3R). Genetic model fitting was performed to estim ate the magnitude of genetic and environmental contributions to the lifetim e co-occurrence of DSM-III-R PTSD, AD and DD. The liability for PTSD was pa rtially due to a 15.3% genetic contribution common to AD and DD and 20.0% g enetic contribution specific to PTSD. Risk for AD was partially due to a 55 .7% genetic contribution common to PTSD and DD. Genetic influences common t o PTSD and AD accounted for 25.2% of the total risk for DD. Specific family environmental influence accounted for 33.9% of the total variance in risk for DD. Remaining variance for all three disorders was due to unique enviro nmental factors both common and specific to each phenotype. These results s uggest that PTSD, AD and DD each have etiologically distinct components and also have significant genetic and unique environmental contributions in co mmon. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.