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Endocrine, Metabolic, and Genetic Disorders

A 6-month old presents to the emergency center with seizures. The family denies fever and trauma, but does note the infant has had intermittent emesis for the last several weeks and has become progressively irritable and lethargic. They report no sick contacts or travel. The only recent change in the infant’s routine has been the introduction of baby foods and fruit juice after the 6-month checkup 1 week ago. On physical examination the temperature is 37°C (98.6°F), heart rate is 120 beats per minute, respiratory rate is 25 breaths per minute, and blood pressure is 90/55 mm Hg. She is irritable, but consolable and mildly jaundiced. Head is without trauma. Neck is supple. The mucous membranes are pink, moist, and without lesions. Pupils are equally round and reactive; sclera are icteric. The chest is clear. Heart has a normal S1 and S2 without murmur. The abdomen is soft and nontender. The liver edge is palpable 3 cm below the costal margin. Neurologic examination is nonfocal. Laboratory studies show:

  • Sodium: 140 mEq/L

  • Potassium: 4.5 mEq/L

  • Chloride: 102 mEq/L

  • Bicarbonate: 22 mEq/L

  • Glucose: 50 mg/dL

  • Creatinine: 0.5 mEq/L

  • Blood urea nitrogen (BUN): 10 mEq/L

  • Aspartate aminotransferase (AST): 95 IU/L

  • Alanine aminotransferase (ALT): 110 IU/L

  • Albumin 2.5 g/dL

  • Urinalysis: specific gravity 1.010, glucose, protein, white cells negative; reducing substances positive

Which of the following is likely to explain this infant’s condition?

a. Tyrosinemia

b. Galactosemia

c. Hereditary fructose intolerance

d. α1-Antitrypsin deficiency

e. Glucose-6-phosphatase deficiency

The answer is c. (Hay et al, p 999. Kliegman et al, pp 727-728. Rudolph et al, pp 608-609.) The patient in the question has new symptoms of emesis, irritability, and lethargy along with low serum glucose and albumin, elevated serum liver function studies, and reducing substances in the urine. These changes are likely due to hereditary fructose intolerance, manifest only when fructose in fruit juice is provided in the diet. Galactosemia, fructosemia, tyrosinosis, and glucose-6-phosphatase deficiency represent diseases in which a congenital deficiency of enzyme causes an interruption of a normal metabolic pathway and an accumulation of metabolic precursors that damage vital organs. Galactose (found in milk) and fructose (found in fruit juices) produce urinary reducing substances in their respective disorders. The mode of inheritance of galactosemia, fructosemia, and most forms of glucose-6-phosphatase deficiency is autosomal recessive. In galactosemia and fructosemia, errors in carbohydrate metabolism cause the accumulation of toxic metabolites when specific dietary sugars are introduced (lactose in galactosemia; fructose and sucrose in fructosemia). Exclusion of the offending carbohydrate from the diet will prevent liver damage. In tyrosinemia type I, or tyrosinosis, the accumulation of tyrosine and its metabolites is ...

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