A 3-day-old boy is brought to the office due to poor feeding, vomiting, and progressive lethargy. The parents also report that his diapers have a "burnt sugar smell" differing from their previous children's diapers. The mother and infant were discharged from the hospital yesterday after a normal pregnancy and spontaneous vaginal delivery. The mother is exclusively breastfeeding. Her other 2 children are healthy and have no medical problems. Physical examination shows a lethargic infant with dry mucous membranes and generalized hypertonia. Which of the following should be restricted from this infant's diet?

Question

A 3-day-old boy is brought to the office due to poor feeding, vomiting, and progressive lethargy.  The parents also report that his diapers have a "burnt sugar smell" differing from their previous children's diapers.  The mother and infant were discharged from the hospital yesterday after a normal pregnancy and spontaneous vaginal delivery.  The mother is exclusively breastfeeding.  Her other 2 children are healthy and have no medical problems.  Physical examination shows a lethargic infant with dry mucous membranes and generalized hypertonia.  Which of the following should be restricted from this infant's diet?

Quizplus · Accepted Answer

11ec160b_36cb_7f99_9249_7b9859273228_MD0001_00 This infant has symptoms typical of maple syrup urine disease (MSUD), an autosomal recessive inborn error of metabolism due to branched-chain α-ketoacid dehydrogenase complex (BCKDC) deficiency. This enzyme normally allows for the breakdown of leucine, isoleucine, and valine into substrates for entry into the TCA cycle. BCKDC deficiency is neurotoxic primarily due to elevated levels of leucine. Infants present in the first few days of life with progressive irritability, poor feeding, lethargy, and increased muscle tone. The urine characteristically has a sweet, "maple syrup" odor. Diagnosis can be confirmed by the presence of elevated branched-chain amino acid levels. Therapy consists of dietary restriction of branched-chain amino acids, but patients remain at lifelong risk for neurotoxicity in the setting of intercurrent illnesses and fasting. (Choice A) Galactosemia is an autosomal recessive disorder due to galactose-1-phosphate uridyltransferase deficiency. The buildup of galactose (normally found in breast milk and regular infant formula) leads to neonatal jaundice, cataracts, hepatomegaly, and frequently Escherichia coli sepsis. Dietary restriction of galactose is the mainstay of treatment. (Choice C) Homocystinuria is an autosomal recessive disorder marked by a defect in cystathionine β-synthase, resulting in elevated levels of homocysteine and methionine. Restriction of methionine for these patients is one aspect of therapy. (Choice D) Phenylketonuria is an autosomal recessive disorder characterized by phenylalanine hydroxylase deficiency, leading to hyperphenylalaninemia. Untreated patients develop intellectual disability, seizures, decreased hair/skin pigmentation, and a "musty" odor. (Choice E) Dietary tyrosine restriction may be beneficial for patients with hypertyrosinemia (progressive liver and renal disease) or alkaptonuria (pigmented osteoarthritis). Educational objective: Maple syrup urine disease classically presents with irritability, dystonia, poor feeding, and a "maple syrup" scent to the patient's urine within the first few days of life. Dietary restriction of branched-chain amino acids (eg, leucine, isoleucine, valine) is the hallmark of treatment. __________ References: Branched-chain amino acid metabolism: From rare Mendelian diseases to more common disorders. (http://www.ncbi.nlm.nih.gov/pubmed/24651065) Maple syrup urine disease. (http://www.ncbi.nlm.nih.gov/pubmed/20301495)

A 3-Day-Old Boy Is Brought to the Office Due to Poor