PSEN1 and hyperinsulinemic hypoglycemia, familial, 4: If PS-1 dysregulation indeed is a factor in the development of neuropathology in HPRT deficiency, it seems unlikely that its role is through accumulation of a toxic Aβ42, since no histopathological evidence has ever been provided for accumulation of Aβ or other storage materials in the brain of LND patients or in the HPRT knockout mouse.