Abstract
It is a common observation that individuals differ greatly in their consumption of alcohol and, if they do drink, in their sensitivity to it. Comparison of identical (MZ) and non-identical (DZ) twins is perhaps the best available design for estimating the relative contributions of environmental and genetic factors to individual differences. We have studied drinking habits in 3,810 adult twin pairs who responded to a mailed questionaire. Genetic factors are of major importance in determining the alcohol consumption of females of all ages but are modified in their expression by marriage. They are also important in young males but are overshadowed by environmental influences shared by brothers as they get older. In a laboratory study of alcohol metabolism and psychomotor sensitivity in more than 200 twin pairs we found heritabilities of 0.62 for peak BAC and 0.49 for rate of elimination. These did not differ significantly from their respective test-retest reliabilities, which were surprisingly low, indicating the importance of short-term environmental influences on ethanol metabolism. For certain psychomotor tests, particularly body sway, we found evidence that sensitivity to alcohol was strongly genetically determined. However, only 2 per cent of variance was accounted for by blood alcohol concentration. Two possible interpretations of our results are :- i) the psychomotor tests we have used have little to do with driving competence and therefore our results are irrelevant for practical purposes, or ii) roadside tests of driving competence will be a more effective preventive measure than measuring concentrations of alcohol or other drugs in the blood.
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N.G. Martin
Both authors formerly Public Health Officers, Eastern Sydney Area Public Health Unit Previously general practitioner, Orange NSW, Australia.