A twin study of psychomotor performance during alcohol intoxication: early results.

It Is a commonplace observation that some people are greatly affected by even small doses of alcohol while others seem relatively tolerant to even large doses. How much of this variation in susceptibility to intoxication is genetically deter-mined? Are there environmental factors that influence susceptibility to alcohol? In an attempt to answer-these <iueStio~, we aremeaS"uOi'ig f8-3S-year-old twins on a number of psychomotor tasks related to driving skills including motor coordination , body sway, hand steadiness, reaction time, and cognitive impairment before and after ingestion of alcohol. Our sample includes healthy twins of both sexes resident in Sydney and aged between 18 and 35. Each twin participating attends a testing session beginning about 9:00 AM, having eaten a light, nonfatty breakfast about an hour earlier. Four sets of variables are measured during an 8-hour session: personality and drinking history , parameters of the blood ethanol profile, and physiological and behavioural responses following ethanol ingestion. Before testing begins, a 20-00 blood sample " and a urine sample are collected; one aliquot of blood is used for typing to establish zygosity and another aliquot of blood and the urine Sample are used for quantitative haematological and biochemical assays, including mean corpuscular volume and plasma levels of gamma-glutamyl transpeptidase, aspartate amino-transferase, alkaline phosphatase, and triglycerides, all of which are putative indicators of previous drinking experience [8]. Subjects are trained on apparatUs uSed to test psychomotor "performance and then "prealcohol" (To) measurements are taken of all the physiological and behav-ioural tests. They are then given an alcohol dose of 0.75 g ethanoVkg body weight diluted to 10070 v/v in sugarless lemon squash (equivalent to about 7f.J to a full