POLG and cancer: DNA methylation can be quantitatively assessed as de novo DNA methylation and demethylation by determining levels of enrichment for 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC), respectively 32 through immunoprecipitation of methylated DNA (MeDIP).33 We have determined whether cancer cells are more extensively DNA methylated at exon 2 of POLGA, which would restrict mtDNA copy number to low levels and promote cell proliferation.