PRPS1 and Lethal ataxia with deafness and optic atrophy: Gain-of-function in hPRPS1 causes PRPS1 superactivity via the alteration of allosteric sites I and II, affecting either the trimer or the dimer interfaces, whereas the loss-of-function mutations in hPRPS1 result in the following neurological disorders: Arts syndrome, CMTX5 and DFNX1/DFN2.