Since dPRPS has 89% protein sequence identity with the mammalian PRPS1 (S1A Fig) and the in vivo consequence of the patient-derived mutations has not been directly tested, we generated dPRPS alleles that carry mutations identified from Arts syndrome, dPRPSQ165P and dPRPSR228W [2, 16]. The gene discussed is PRPS1; the disease is Lethal ataxia with deafness and optic atrophy.