observed in AUD subjects are attributable to alcohol consumption or due to comorbid nicotine or drug use, or other psychiatric disorders. When analyzing AUD-associated DNA methylation changes, we can exclude those subjects who use illicit drugs of abuse or are affected with psychiatric disorders, or alternatively, adjust analytically for comorbid phenotypes. Nevertheless, if we exclude those subjects who are also smokers, the sample size for the study will be significantly reduced: individuals with AUDs are four times more likely to be smokers than those without AUDs, and nearly 23% of smokers met past-year criteria for AUDs.111–113 To identify AUD-specific DNA methylation changes, we need to use a sample of AUD case and control subjects who are matched in smoking status and consider the status of smoking as a confounding factor in the data analysis.
