Shortly after birth, an infant presents with severe lactic acidemia, hyperammonemia, citrullinemia, and hyperlysinemia with the presence of a-ketoglurate in the urine. Tests are performed to determine where the defect lies that is causing this cluster of symptoms. These tests indicate that the infant does not have a urea cycle defect, nor a defect in fatty acid oxidation. A defect in which of the following metabolic pathways is most likely the cause of this infants symptoms?
A) bile acid synthesis
B) branched-chain amino acid catabolism
C) gluconeogenesis
D) glycogen synthesis
E) glycolysis

Question

Quizplus · Accepted Answer

The infant is experiencing symptoms associated with a defect in pyruvate carboxylase. Pyruvate carboxylase is the first enzyme in the gluconeogenic conversion of pyruvate carbons into glucose. A defect in pyruvate carboxylase would restrict the conversion of lactate into pyruvate and then subsequently to glucose. This would lead to severe lactic academia. The other symptoms are primarily the result of liver damage due to impaired gluconeogenesis.

Shortly After Birth, an Infant Presents with Severe Lactic Acidemia