PRPS1 and Lethal ataxia with deafness and optic atrophy: PRS-I deficiency is an extremely rare condition that can lead to three different disorders: Arts syndrome (MIM 301835), being the most extreme form of enzyme deficiency; Rosenberg-Chutorian syndrome or X-linked Charcot-Marie Tooth 5 (CMTX5, MIM 311070), which represents a less severe phenotype; and X-linked non-syndromic sensorineural deafness (DFN2, MIM 304500), as the mildest form of deficiency.