ATP6AP2 mutations are found in X-linked ID with Parkinsonism and spasticity, and PRPS1 mutations in Arts syndrome, X-linked recessive Charcot-Marie-Tooth disease 5 and X-linked non-syndromic hearing loss [11,55,56,57,95,96,97,98]. The gene discussed is PRPS1; the disease is Lethal ataxia with deafness and optic atrophy.