These variable findings obtained in different populations support the notion of genetic heterogeneity of EEG variation suggested by the first linkage study (Anokhin et al., 1992). Importantly, other studies have provided evidence for functional significance of the LVEEG variant. Enoch et al. reported the association between the LVEEG phenotype, anxiety disorders, and alcoholism, with the strongest association observed for a subtype of alcoholism associated with anxiety disorders (Enoch et al., 1995; Enoch et al., 1999). Finally, it should be noted that the prevalence of the LVEEG phenotype shows considerable differences across different human populations and ethnic groups (Anokhin et al., 1992; Ehlers and Phillips, 2003; Ehlers et al., 2004). This observation has important implications for association studies, since group differences in both the frequency of the phenotype and the frequency of a genetic variant can lead to spurious association (see section 6.2.2). Thus, categorical approach to phenotypic characterization of the human EEG based on the identification of specific patterns of activity can be an alternative to the analysis of separate quantitative characteristics, however, there is a need for more accurate
