APRT and hyperinsulinemic hypoglycemia, familial, 4: Since the identification of dihydroxyadenine stones or crystals is pathognomonic for adenine phosphoribosyltransferase deficiency, measurement of adenine phosphoribosyltransferase activity in erythrocytes, genetic testing or quantification of dihydroxyadenine in urine are not mandatory for diagnosis [4].