Class B-I genes (excluding ASCL2, NPY, and SLC5A8 genes, whose promoter DNA hypermethylation in hESC lines could be due to the in vitro culture process [11]) are frequently hypermethylated in hESCs and cancer cells lines but never in normal tissues, which suggests that the loss of methylation at the promoters of these genes might be an important influence on the loss of pluripotency during development. This evidence concerns the gene SLC5A8 and cancer.