MSMB and Lethal ataxia with deafness and optic atrophy: Therefore, to better understand the in vivo function of PRPS and to directly assess the physiological consequence of patient-derived mutations, we engineered two dPRPS alleles that carry the mutations identified from Arts syndrome via CRISPR/Cas9: dPRPSQ165P and dPRPSR228W (S2A Fig and Fig 2A).