DNA methylation occurs when DNA methyltransferases (DNMT) catalyze the covalent addition of a methyl group (-CH3) to the 5-carbon of cytosine resulting in 5-methylcytosine (5-mC). Its primary function is to regulate gene expression either by recruiting proteins involved in gene expression, such as histone deacetylases and other chromatin remodeling proteins, or by inhibiting transcription factors from binding to DNA and initiating transcription.