Another neurotransmitter system involved in the actions of alcohol is acetylcholine, which can interact with different types of receptors, including muscarinic and nicotinic receptors. As with the GABA-A receptor, the subunits for each of these receptors are encoded by different genes that have several different alleles (i.e. code for different forms of the receptor subunit), and certain alleles have been associated with an increased risk for alcoholism. For example, the gene that encodes the muscarinic acetylcholine receptor subtype 2, called CHRM2, appears to be an important risk factor for alcohol dependence. The receptor encoded by this gene is a G-protein–coupled receptor6 involved in many functions. In the COGA study, SNPs in CHRM2 were associated with alcohol dependence, a finding that was replicated in an independent study (Edenberg and Foroud 2006).
