One ERO endophenotype for genetic studies, event-related theta power, has been examined in densely affected alcoholic families in the large Collaborative Study on the Genetics of Alcoholism (COGA). The densely affected families consisted of a proband and two additional first-degree relatives affected with alcohol dependence (DSM-IV), and control families that were randomly ascertained from the general population. These studies reported significant linkage and association between the CHRM2 (cholinergic muscarinic receptor M2) gene on chromosome 7 and frontal theta oscillations to target stimuli in a visual oddball task. Association analyses using both population based tests (Measured Genotype) and pedigree based tests (Quantitative Pedigree Disequilibrium Test, QPDT) indicated significant association of the frontal theta band ERO phenotype with several single-nucleotide polymorphisms (SNPs) surrounding exon 4 of CHRM2. Further, an examination of the slower frequency parietal delta band ERO revealed significant association with several SNPs surrounding the coding region of the CHRM2 gene [179,180].
