MSMB and Lethal ataxia with deafness and optic atrophy: Three clinical phenotypes are associated with loss-of-function <i>PRPS1</i> variants and decreased PRPS activity: Arts syndrome (OMIM: 301835), Charcot-Marie-Tooth disease type 5 (CMTX5, OMIM: 311070), and nonsyndromic X-linked deafness (DFN2, OMIM: 304500).