High levels of BUN and serum creatinine were found in all HPRT-/- mice treated with allopurinol (S1 Fig), confirming that these animals were affected by severe renal failure, whereas vehicle-treated mice, as well as allopurinol-treated HPRT+/- and WT animals, had normal renal function. The gene discussed is HPRT1; the disease is acute kidney injury.