PRPS1 and retinitis pigmentosa: 30 mutations in the PRPS1 coding region have been reported thus far: 11 cause DFNX1, 10 cause Charcot-Marie-Tooth disease-5 (CMTX5), 9 cause Phosphoribosyl pyrophosphate synthetase 1 (PRS-1) superactivity, 5 cause Arts syndrome, and 4 cause other phenotypes (e.g., retinitis pigmentosa, cone-rod dystrophy, or peripheral neuropathy with HL).