Sex differences in expression of the X chromosome encoded and cancer metabolism-related genes glucose-6-phosphate dehydrogenase (G6PD) and O-Linked N-acetylglucosamine (GlcNAc) transferase (OGT), differ at both the mRNA and protein level in the blastocysts of multiple species and are correlated with measurable differences in glucose metabolism [141–143]. This evidence concerns the gene G6PD and cancer.