PRTFDC1 (phosphoribosyltransferase domain-containing protein 1), also known as HHGP, is a 225 amino acid protein that belongs to the purine/pyrimidine phosphoribosyltransferase family.The functions of PRTFCD1 are not well understood; however it has been suggested that it is frequently silenced in oral squamous-cell carcinomas by aberrant promoter hypermethylation. Conserved in vertebrates, PRTFDC1 is suggested to be a possible tumor-suppressor. PRTFDC1 is encoded by a gene which maps to chromosome 10. Spanning nearly 135 million base pairs, chromosome 10 makes up approximately 4.5% of the total DNA in cells and encodes nearly 1,200 genes. Three isoforms of PRTFDC1 exist due to alternative splicing events. Has low, barely detectable phosphoribosyltransferase activity (in vitro). Binds GMP, IMP and alpha-D-5-phosphoribosyl 1-pyrophosphate (PRPP). Is not expected to contribute to purine metabolism or GMP salvage.