Fasting hypoglycemia with hepatomegaly in an 11-month-old
An 11-month-old girl is brought after two early-morning episodes in which she was difficult to rouse and sweaty; each resolved within 20 minutes after breastfeeding. She was born at term, has been breastfed on demand with complementary foods since 6 months, and now weighs 7.8 kg (below the 3rd percentile). Her liver edge is 4 cm below the right costal margin and her abdomen is otherwise soft. Fasting for 4 hours during the evaluation produced glucose 34 mg/dL, lactate 4.8 mmol/L, triglycerides 420 mg/dL, uric acid 9.2 mg/dL, ammonia 38 micromol/L, and trace urine ketones. ALT is 42 U/L and creatinine is 0.3 mg/dL. Blood gas shows pH 7.30 with bicarbonate 17 mmol/L. She has no dysmorphic features and her development is appropriate for age.
1. Which metabolic disorder best explains this, and how do the ketones, lactate and uric acid discriminate between the alternatives?
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The pattern is fasting hypoglycemia with hepatomegaly, lactic acidosis, hyperuricemia, hypertriglyceridemia and inappropriately low ketones, which is the classic profile of glycogen storage disease type Ia (glucose-6-phosphatase deficiency). The mechanism explains each number: glucose-6-phosphate cannot be converted to free glucose, so fasting produces hypoglycemia; the accumulated glucose-6-phosphate is shunted into glycolysis (lactate) and the pentose phosphate pathway (uric acid), while low insulin and abundant substrate drive lipogenesis (triglycerides). Ketones are low because hepatic fatty acid oxidation is suppressed by malonyl-CoA generated from the excess cytosolic substrate.
This is why hypoketotic hypoglycemia should not automatically be labeled a fatty acid oxidation defect. In fatty acid oxidation disorders there is usually no massive hepatomegaly, creatine kinase and free fatty acids are elevated, ammonia may be high, and uric acid and lactate are not the dominant features. Fructose-1,6-bisphosphatase deficiency causes fasting lactic acidosis but not marked hyperuricemia, hypertriglyceridemia, or hepatomegaly, and hypoglycemia is less prominent. Confirmation is by G6PC sequencing or liver enzyme assay.
2. Write the acute and long-term management plan, including dietary restrictions and surveillance.
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Acutely, give 2-3 mL/kg of 10% dextrose slowly to correct symptomatic hypoglycemia, then a continuous infusion of 10% dextrose at about 1.5 times maintenance to keep glucose above 70 mg/dL, and recheck glucose in 30 minutes. Avoid bicarbonate unless acidosis is severe and unresponsive, since it can worsen intracellular acidosis, and avoid lactate-containing fluids.
For the long term, restrict fructose and galactose strictly: no sucrose, fruit, juice, honey, sorbitol or regular sweetened formula, because these cannot be converted to glucose and worsen lactic acidosis. Under 1 year, use frequent daytime feeds of glucose polymer with a continuous overnight nasogastric glucose infusion; cornstarch at 1.6-2 g/kg/dose every 3-4 hours becomes practical after about 1 year as amylase activity matures. Add allopurinol if uric acid stays high, and consider lipid-lowering therapy if triglycerides remain above 500-1000 mg/dL.
Surveillance includes liver ultrasound and alpha-fetoprotein every 6-12 months for adenomas, renal function and microalbuminuria, growth, and developmental review. Involve a metabolic dietitian and provide a written emergency plan.
3. The child develops vomiting and fever at home. What is the sick-day plan and what mistake must be prevented?
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The highest-risk situations are gastroenteritis, fever and any period of reduced intake, because hepatic glucose release fails within about 3-4 hours of fasting and the child can become hypoglycemic and acidotic at home. Provide a written emergency plan: check glucose at the start of any illness and every 3-4 hours, offer glucose-containing fluids (breast milk, glucose polymer solution, or oral rehydration solution) every 2-3 hours, and come to hospital if vomiting prevents intake, if glucose falls below 70 mg/dL, or if she becomes drowsy or breathes fast.
If vomiting persists, place a nasogastric drip of 10% dextrose at maintenance and admit rather than attempting repeated oral feeds at home. Warn the family explicitly against juices, sweetened drinks and honey, which worsen lactic acidosis without raising glucose.
The preventable mistake is that the first clinician to see her treats this as simple gastroenteritis and gives only saline without glucose, causing hypoglycemia and acidosis. Give the family a diagnosis card and an emergency letter for the local hospital, and register her with the metabolic team so that any admission triggers early contact with a metabolic center.