Glycolysis

A 3-year-old boy from rural Maharashtra presents with recurrent episodes of severe hypoglycemia (blood glucose 35 mg/dL) occurring 3–4 hours after meals, accompanied by seizures and loss of consciousness. His parents report that he remains asymptomatic during fasting periods >8 hours. Physical examination reveals hepatomegaly. Serum lactate is elevated at 6 mmol/L (normal <2). A random blood glucose during a symptomatic episode is 32 mg/dL with simultaneous serum insulin 2 mIU/L (inappropriately low). Which is the most appropriate immediate next step in management?

A 7-year-old boy from Mumbai presents with recurrent episodes of dark urine and jaundice after strenuous play. Enzyme assay shows normal hexokinase and phosphofructokinase activity. Which finding best distinguishes his condition from phosphofructokinase deficiency?

A 28-year-old woman from Delhi presents with acute onset of severe muscle pain, dark urine, and myoglobinuria following intense exercise at a gym. Serum creatine kinase is 8,500 U/L (normal <200). Blood glucose is 78 mg/dL, lactate is 1.2 mmol/L (normal), and venous pH is 7.38. Muscle biopsy shows subsarcolemmal glycogen accumulation and absent acid maltase activity. Which glycolytic/glycogenolytic enzyme deficiency would explain the normal lactate despite severe muscle breakdown?

A 3-year-old boy from rural Maharashtra presents with recurrent episodes of severe hypoglycemia, lactic acidosis (pH 7.1, lactate 8 mmol/L), and hepatomegaly. His parents report that symptoms worsen during fasting and improve with frequent meals. Serum pyruvate is elevated at 4.2 mg/dL (normal <2). Blood glucose during a fasting challenge drops to 32 mg/dL within 4 hours. Liver biopsy shows glycogen accumulation. Which enzyme deficiency best explains this clinical presentation?

Which enzyme catalyzes the first committed step of glycolysis and is the primary site of allosteric regulation?