Such mtDNA hypermethylation in PCOS may be linked to hyperhomocysteinemia and subsequent significant upregulation of the one-carbon metabolic enzymes betaine homocysteine methyltransferase (BHMT) and glycine N-methyltransferase (GNMT) and the DNA methyltransferase DNMT1 [62]. Here, GNMT is linked to hyperhomocysteinemia.