Review Question - QID 107974

A 2-year-old boy presents to the emergency department with new onset seizures. After controlling the seizures with fosphenytoin loading, a history is obtained that reveals mild hypotonia and developmental delay since birth. There is also a history of a genetic biochemical disorder on the maternal side but the family does not know the name of the disease. Physical exam is unrevealing and initial lab testing shows a pH of 7.34 with a pCO2 of 31 (normal range 35-45) and a bicarbonate level of 17 mg/dl (normal range 22-28). Further bloodwork shows an accumulation of alanine and pyruvate. A deficiency in which of the following enzymes is most likely responsible for this patient's clinical syndrome?