GSD type I (von Gierke disease)

Pathophysiology - Sugar Stuck Inside

• Primary Defect: Deficiency of Glucose-6-phosphatase in the liver, kidneys, and intestinal mucosa.
• Metabolic Block: The final step of gluconeogenesis & glycogenolysis is blocked: $G6P \nrightarrow Glucose$.
• Consequences: Glucose-6-phosphate gets "stuck" inside hepatocytes, leading to:
  • Severe fasting hypoglycemia.
  • G6P accumulation and shunting into other pathways.

⭐ Severe fasting hypoglycemia is the hallmark, often presenting within the first few months of life with seizures.

Clinical Features - Big Liver, Hangry Baby

• Presentation (3-6 months): Doll-like facies (fat cheeks, thin extremities), short stature, and a protuberant abdomen from massive hepatomegaly (glycogen buildup).
• Severe Fasting Hypoglycemia: Central, life-threatening feature. Leads to irritability, seizures, and lethargy if feedings are spaced.
  • Blood glucose often < 60 mg/dL.
• Key Metabolic Derangements:
  • ↑ Lactic acidosis (shunting of G6P).
  • ↑ Hyperuricemia → Gout in adolescence/adulthood.
  • ↑ Hyperlipidemia (milky/lipemic serum).
• Renal: Nephromegaly due to glycogen deposition, risking dysfunction over time.
• Hematologic: Impaired platelet function → bleeding tendency (e.g., epistaxis).

⭐ Patients often present with seizures due to profound hypoglycemia, a key feature distinguishing it from GSDs with milder hypoglycemia.

Diagnosis - The Proof is in the Labs

• Blood & Urine Panel:

  • ↓↓ Severe fasting hypoglycemia
  • ↑↑ Lactic acidosis
  • ↑↑ Hyperuricemia
  • ↑↑ Hyperlipidemia (esp. triglycerides)
  • Ketones are notably absent or low in urine/blood.

• Diagnostic Flow:

⭐ Glucagon Challenge Test: A hallmark finding is the failure of blood glucose to rise after glucagon administration, coupled with a paradoxical, sharp increase in blood lactate levels. This confirms a block in the final steps of gluconeogenesis and glycogenolysis.

Management - The Cornstarch Cure

• Primary Goal: Maintain normoglycemia (blood glucose >70 mg/dL) to prevent acute crises and support normal growth.
• Dietary Regimen:
  • Frequent daytime meals + continuous nocturnal glucose infusion (e.g., via NG tube) in infants.
  • Uncooked Cornstarch: Administered every 4-6 hours; acts as a slow-release glucose source, bypassing the enzyme defect.
• Dietary Restrictions:
  • Avoid fructose, sucrose, and galactose (lactose). These sugars are metabolized to glucose-6-phosphate, exacerbating intracellular accumulation.
• Pharmacotherapy:
  • Allopurinol: To control hyperuricemia and prevent gout.

⭐ The core principle is providing a constant exogenous source of glucose, like uncooked cornstarch, to bypass the defective endogenous glucose production (both glycogenolysis and gluconeogenesis).

High‑Yield Points - ⚡ Biggest Takeaways

• Deficiency in glucose-6-phosphatase, the final step of gluconeogenesis & glycogenolysis.
• Presents at 3-4 months with severe fasting hypoglycemia, lactic acidosis, and seizures.
• Classic findings include a protuberant abdomen (massive hepatomegaly), doll-like facies, and thin extremities.
• Lab results show hyperuricemia, hyperlipidemia (↑ triglycerides), and ↑ blood lactate.
• Treatment involves frequent oral glucose/cornstarch and avoiding fructose and galactose.