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Smoking Affects DNA Methylation Levels in Blood, Twin-Based Study Finds

Researchers have uncovered more than a dozen sites that are differentially methylated between smoking and non-smoking identical twins. Previous studies had found such discordant methylation between smokers and non-smokers but by focusing on monozygotic twins, researchers from Vrije Universiteit Amsterdam aimed to account for possible genetic predispositions to smoking and focus on methylation patterns that arise in response to smoking. As they report in the journal eLife, the researchers analyzed DNA methylation data from 769 monozygotic twin pairs to uncover 13 differentially methylated CpG sites between smoking and non-smoking identical twins. These sites include ones in CACNA1D and GNG12, which encode proteins that interact with the nicotinic acetylcholine receptor, which the researchers say indicates they might be reactive to nicotine exposure. By also examining DNA methylation profiles of twins who are both smokers but differ in the number of cigarettes they smoke, the researchers also found differences in DNA methylation patterns. "[B]y analysing data from monozygotic twins, we robustly demonstrate that DNA methylation level in human blood cells is reactive to cigarette smoking," the researchers write.