As allopurinol is administered to LND patients as soon as possible after birth, we hypothesized that allopurinol treated HPRT-/- mice could represent a better model of the human disease and provide insights into the consequences of free purine accumulation in the presence of HPRT-deficiency. This evidence concerns the gene HPRT1 and hyperinsulinemic hypoglycemia, familial, 4.