DO GENES INFLUENCE EXPOSURE TO TRAUMA - A TWIN STUDY OF COMBAT

Data from 4,029 male-male twin pairs who served in the United States m ilitary during the Vietnam era (1965-1975) were used to examine geneti c and non-genetic factors that influence wartime exposure to traumatic events. Specific events examined were volunteering for service in Vie tnam, actual service in Southeast Asia, a composite index of 18 combat experiences, and information from military records about being awarde d combat decorations. Correlations within monozygotic (MZ) and dizygot ic (DZ) twin pairs for volunteering for service in Vietnam were 0.40 a nd 0.22, respectively. For actually serving in Southeast Asia, the MZ correlation was 0.41 and the DZ correlation was 0.24. Analysis of twin pairs in which both siblings served in Southeast Asia (n = 820) demon strated a correlation for self-reported combat experiences within MZ a nd DZ pairs of 0.53 and 0.30, respectively. Heritability estimates ran ged from 35 to 47%. The family environment did not have a significant effect on any of the variables. Analyses of data from military records regarding being awarded a combat decoration provided very similar res ults to those found for self-reported combat experiences.