The present findings based on auditory P300 confirm our previous analyses showing an association between lower visual P300 amplitude and familial risk for alcohol dependence. The present report found an association between genetic variation of the CHRM2 rs1824024 SNP in the 8–12 year old group and not in the older age groups. This may represent a greater influence that muscarinic receptors might have in younger children. Alternatively, environmental effects on P300 amplitude should be considered. Van Beijsterveldt et al., (1999) have noted that biometrical modeling of ERP data for adolescent twins reveals both genetic and environmental variance with approximately 50% of the variance in P300 amplitude explained by genetic factors while the other proportion appears to be environmental. Possibly environmental influences that accrue with advancing age may dampen the impact of specific genetic variation, here variation in intron 4 of the CHRM2 gene.
