Another endophenotype that has been described is related to an individual's sensitivity to a given substance. A lowered individual sensitivity to alcohol has been demonstrated to be an inherited factor that affects the likelihood of drinking and mediates, in part, the disposition for developing alcoholism [15]. In one empirical study, California Indian participants, like Caucasian sons of alcoholics, were found to have less intense objective and subjective effects of alcohol in an alcohol challenge paradigm. Additionally, participants with at least 50% Native American heritage reported less intense effects of alcohol than did those with less than 50% Native American heritage, despite equivalent blood alcohol concentrations [14]. Further, Ehlers and colleagues [42] asked participants in the California Indian population to provide retrospective reports of their responses to alcohol during the first five times they had ever drank alcohol using the Self-Rating of the Effects of Alcohol (SRE) questionnaire. A linkage analysis using these responses as the phenotype, revealed loci on chromosomes 6q25.2 and 9p24.1 that had a LOD score greater than 3.0. Like the EEG studies previously described, these studies provide
