Two additional studies using EEG frequency measures as endophenotypes for substance use disorders were conducted in the Plains Indian population. In the first study, the authors conducted a genomewide linkage study that yielded significant evidence of linkage to a region of chromosome 5q13-14 containing the corticotropin releasing hormone-binding protein gene (CRHBP). Follow-up association studies suggested a relation between polymorphisms in this gene and alcoholism in a Caucasian sample but not in the Plains Indian population. In the second study, the authors conducted a genomewide association scan of EEG power phenotypes. Significant associations were observed between theta power and polymorphisms in the SH3-domain GRB2-like (endophilin) -interacting protein 1 gene (SGIP1) on chromosome 1p31.3 that also yielded an association with alcohol dependence in this sample [39]. Notably, this was not replicated in the COGA dataset [41]. Though preliminary, the studies conducted in the California Indian and Plains Indian populations demonstrate the utility of EEG phenotypes in identifying genetic loci that confer risk for these disorders.
