Missense mutations in the PRPS1 gene have resulted in the classification of four distinct nonsyndromic and syndromic forms of hearing loss: PRS-I superactivity (MIM 300661), X-linked nonsyndromic sensorineural hearing loss (DFN-2) (MIM 304500), Charcot-Marie-Tooth disease-5 (CMTX5) (MIM 311070), and Arts syndrome (MIM 301835) (Table 1). The gene discussed is PRPS1; the disease is Arts syndrome.