While the phenotypes of the Hprt−/0/Tg mice do not recapitulate the full spectrum of severe phenotypes observed in LND patients, these results do support a genetic interaction in mice between HPRT and PRTFDC1 in which the presence/absence of PRTFDC1 acts as an enhancer/suppressor of HPRT-deficiency. The gene discussed is PRTFDC1; the disease is hyperinsulinemic hypoglycemia, familial, 4.