Finally, Retinol-binding protein 1, a downstream target of RAR, has recently been shown to become hypermethylated following knock-in of a mt IDH1 gene into a cancer cell line26 and we have confirmed hypermethylation of the Retinol-binding protein 1 promoter and associated downregulation of gene expression in IDH mt CS. The gene discussed is IDH1; the disease is cancer.