The heritability of alcoholism symptoms: "Indicators of genetic and environmental influence in alcohol-dependent individuals" revisited

There is consistent evidence from twin and adoption studies implicating gen etic factors in the etiology of alcoholism, yet few studies have examined t he role of genetic influences on individual symptoms of alcoholism. In a pr evious study of 113 male twins, Johnson et al. (1996a) identified 7 alcohol ism symptoms that were more "genetic" and 14 that were more "environmental" (that is, non-genetic) in their etiology by examining symptom concordances among monozygotic and dizygotic twin pairs. The present study represents a n attempt to replicate the results of this previous study and extend them b y estimating the contribution of genetic factors to the variation in liabil ity for different alcoholism symptoms. Subjects were 3356 male twin pairs f rom the Vietnam Era Twin Registry. Lifetime histories of alcoholism symptom s were assessed by a structured psychiatric telephone interview. The result s of the previous study were not replicated. The correlations between sympt om classifications as genetic and non-genetic in the present and previous s tudy were nonsignificant and ranged from -0.27 to 0.11. However, within the present study the correlation between symptom classifications as genetic a nd non-genetic was statistically significant across random split-half subsa mples (r = 0.59); nine alcoholism symp toms were consistently classified as genetic and six symptoms-as non-genetic in their etiology. Model-fitting a nalyses applied to different alcoholism symptoms yielded heritability estim ates ranging from 0.03 to 0.53 with broad and overlapping confidence interv als around these estimates, ranging from 0.00 to 0.65. The results of this study highlight the difficulty of identifying mon or less heritable phenoty pes in twin research, and suggest that it may not be possible to identify s pecific alcoholism symptoms that are more genetic in their etiology than ot hers. Nevertheless, there appears to be potentially important variation in the relative magnitude of genetic influences for individual alcoholism symp toms, and exploring these differences may lead to further insights into the nosology and etiology of alcohol-related problems.