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Endocrine, Metabolic, and Genetic Disorders

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A 6-month old presents to the emergency center with seizures. Thex 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. There have been no ill contacts. The only recent change in the infant's routine has been the introduction of baby foods and fruit juice after the 6-month checkup. On physical examination, hepatomegaly and jaundice are noted. Laboratory studies reveal a sodium 140 mEq/L, glucose 50 mg/dL, albumin 2.5 g/dL, AST 95 IU/L, ALT 110 IU/L, and reducing substances in the urine.

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

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a. Tyrosinemia

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b. Galactosemia

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c. Hereditary fructose intolerance

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d. α1-Antitrypsin deficiency

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e. Glucose-6-phosphatase deficiency

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The answer is c. (Hay et al, p 999. Kliegman et al, p 503. McMillan et al, pp 2189-2190. Rudolph et al, pp 608-609.) The patient in the question likely has 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 associated with severe dysfunction of the liver, kidney, and CNS. Manifestations of acute liver failure can appear in infancy. A chronic form of the disorder presents as progressive cirrhosis and leads to liver failure or hepatoma. Dietary management does not prevent liver disease. Glucose-6-phosphatase deficiency (also known as glycogen storage disease type 1, or von Gierke disease) often presents at 3-4 months of age with failure to thrive, hypoglycemia, hepatomegaly, and acidosis. α1-Antitrypsin deficiency causes liver disease through accumulation of an abnormal protein, caused by a single amino acid substitution in the SERPINA1 gene on the long arm of chromosome 14. It has a variable and bimodal presentation, but the following are common in infancy: cholestasis; bleeding into the CNS, gastrointestinal (GI) tract, or at the umbilical stump; and elevation of transaminase concentrations. Affected children may have chronic hepatitis with cirrhosis and portal hypertension; pulmonary symptoms ...

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