POLD1 and xeroderma pigmentosum: In fibroblasts of the 3 patients, no differences were observed in the protein expression, apart from DPD, of phosphoribosylpyrophosphate amidotransferase (PPAT), xeroderma pigmentosum protein D (XPD), and DNA Polymerase Delta 1 (POLD1), which are known client proteins of CIAO1 and MMS1919,20,22 (Supplemental Figure S10).