Phosphoribosyl transferase domain containing 1 (PRTFDC1) is highly homologous to the hypoxanthine phosphoribosyltransferase (HPRT1) and may have arisen from a gene duplication event of a common ancestor gene. Recently, it was shown that CpG islands in the PRTFDC1 promoter could be hypermethylated in ovarian cancers and oral squamous-cell carcinomas (OSCC), leading to gene silencing. Restoration of PRTFDC1 expression in OSCC inhibited cell growth in colony-formation assays, while knockdown of PRTFDC1 expression in OSCC that expressed the gene promoted cell growth. These results suggest that PRTFDC1 can act as a tumor-suppressor gene. At least three isoforms of PRTFDC1 are known to exist.