Research into the genetics of alcoholism, both in humans and in animal models, has made great strides over the past four decades, and even more approaches are beginning to be evaluated. For example, there is growing interest in studying epigenetic factors—that is, factors which alter certain phenotypes by modifying regulation of gene expression, without, however, changing the gene’s DNA sequence. One such factor that can impact gene expression is methylation of the DNA. Other epigenetic changes alter the packaging of DNA into chromatin. For example, two enzyme families called histone acetyltransferases and deacetylases can be used to alter chromatin structure experimentally, and studies found that when such changes accompany chronic drug administration, they can modify cocaine-related behaviors in rats (Renthal and Nestler 2009). Although similar research on alcohol-related traits still is in its infancy, some studies have found that alcoholic patients exhibited greater levels of DNA methylation of two different genes than nonalcoholics and, consequently, greater reduction in the expression of those genes (Bleich et al. 2006; Bonsch et al. 2005).
