One potential explanation for these discrepant findings is that high prevalence rates of the disorder among Native Americans may make it difficult to detect genetic influences. Alternatively, the heritability of disorders like alcohol dependence may be reduced or difficult to detect, in some populations, because only some aspects of the diagnosis may be heritable. Two symptoms that have been long associated with severe alcohol dependence are withdrawal and tolerance, specified in DSM-IV as alcohol dependence with a “physiological component.” In the California Indian population, evidence for the heritability of DSM-III-R symptoms of alcohol dependence with withdrawal (.71) and symptoms of alcohol dependence associated with heavy drinking (.37) were found to be heritable [20-21] whereas psychosocial problems associated with alcohol dependence were not. These findings are consistent with those of a previous general population twin study demonstrating that some specific alcohol dependence symptoms, including withdrawal symptoms, are more heritable than others, but also differ in that the latter study reported that heritability estimates of specific symptoms did not exceed that of the alcohol dependence diagnosis [22]. These studies suggest that specific
