a newborn infant develops its first cold, and is fussy and cannot eat. after missing a few feedings, the child becomes quite lethargic, and the parents rush the child to the emergency department. blood analysis indicates elevated levels of lactate and uric acid, and significantly decreased levels of glucose. after stabilizing the child with glucose infusions, a glucagon challenge is given to the infant, and blood glucose levels do not increase, but decrease slightly. the accumulation of which metabolite in the liver is most responsible for the elevated uric acid seen in the circulation?