Recurrent Fasting Hypoglycemia With Lactic Acidosis in a Young Adult
A 24-year-old man is brought to the emergency department after a witnessed tonic-clonic seizure at 7:00 AM. He slept through dinner the night before, so the seizure followed roughly 14 hours without food. Point-of-care glucose is 34 mg/dL, and he wakes fully within minutes of intravenous dextrose. Serum studies show lactate 6.2 mmol/L, bicarbonate 17 mmol/L, uric acid 9.8 mg/dL, triglycerides 480 mg/dL, ALT 78 U/L, insulin <2 µIU/mL, C-peptide 0.5 ng/mL, and beta-hydroxybutyrate 3.9 mmol/L; a sulfonylurea screen is negative. He has never used insulin or any hypoglycemic drug, drinks no alcohol, and takes no medications. Since childhood he avoided long runs and had a protuberant abdomen that was never evaluated. His parents are first cousins. Examination shows a soft, nontender liver edge 6 cm below the costal margin, no jaundice, no edema, and a normal neurologic examination.
1. How does this fasting study localize the defect, and why are lactate and uric acid elevated?
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The fasting study tells you what the body is and is not doing. Insulin and C-peptide are both suppressed, so there is no excess insulin, and the negative sulfonylurea screen removes the other common secretagogue. Beta-hydroxybutyrate is 3.9 mmol/L, so fatty acid oxidation and ketogenesis are intact, which argues against a fatty acid oxidation defect - those classically produce hypoketotic hypoglycemia. What remains is failure of endogenous glucose production in a patient with hepatomegaly. Glucose-6-phosphatase is the final shared step of glycogenolysis and gluconeogenesis; without it, glucose-6-phosphate cannot be dephosphorylated and released, so the liver cannot defend blood glucose no matter which substrate is supplied.
The same block explains the rest of the panel. Glucose-6-phosphate accumulates and is pushed into glycolysis, generating pyruvate and lactate, hence lactate 6.2 and bicarbonate 17. ATP depletion and accelerated purine turnover raise uric acid, and lactate competes with urate for renal tubular secretion, further reducing excretion. Excess acetyl-CoA and malonyl-CoA drive triglyceride synthesis, producing the 480 mg/dL triglycerides and the hepatic steatosis behind the ALT of 78. Adult presentation is uncommon but recognized in milder variants, and consanguinity supports a recessive glycogen storage disorder.
2. He must be NPO for 12 hours for a procedure. Outline the fluid plan and the endpoints you would use.
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The trap is treating the glucose number without securing the substrate supply. He needs continuous exogenous glucose because his liver cannot produce any, and that supply must be uninterrupted through the NPO period. Start D10 in water with maintenance electrolytes at roughly 1.5 times maintenance volume, targeting a glucose infusion rate of about 6-8 mg/kg/min. Check bedside glucose hourly until stable, then every 2-4 hours. Avoid lactated Ringer's, which adds an exogenous lactate load to a patient who cannot clear lactate, and avoid any fluid strategy that leaves the dextrose rate inadequate.
Endpoints: glucose above 70 mg/dL at all times, falling lactate, rising bicarbonate, and adequate urine output. When enteral feeding resumes, maintenance consists of frequent carbohydrate-containing feeds by day plus uncooked cornstarch at bedtime, which is slowly digested and provides a sustained overnight glucose source. If enteral intake is interrupted again, the dextrose infusion must be running before the fast begins and must never be stopped abruptly - rebound hypoglycemia in this disorder can be rapid and severe.
3. Which two interventions would you avoid in this patient, and why?
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First, glucagon. Glucagon stimulates glycogen breakdown and gluconeogenesis, but both pathways converge on glucose-6-phosphatase, which he lacks. It will not raise his glucose; it will drive glucose-6-phosphate into glycolysis and worsen the lactic acidosis. Second, fructose, sucrose, and large galactose loads, including fruit juice, table sugar, and standard lactose-containing formula in quantity. These enter glycolysis downstream of the block, so they generate lactate and pyruvate and can precipitate hypoglycemia rather than correct it. Lactose should be limited and replaced with a glucose-based feeding regimen.
Also avoid prolonged fasting, lactate-containing intravenous fluids, and bicarbonate for the acidosis - the acidosis resolves with glucose and time, and bicarbonate risks overshoot alkalosis. Monitor uric acid; allopurinol is used when hyperuricemia is significant. Surveillance for hepatic adenomas, triglycerides, and renal function is part of long-term care. If this were type Ib, neutropenia would be expected and G-CSF would be indicated; type Ia does not cause neutropenia. A medical alert card, a sick-day plan that avoids fasting, and counseling about alcohol are practical parts of management.