Amino acid metabolism and disorders — MCQs

A 10-day-old infant with MSUD is admitted with lethargy, poor feeding, and plasma leucine of 2000 μmol/L (normal <200). Despite BCAA-free formula, the infant's condition worsens with encephalopathy. The neonatology team proposes hemodialysis, while the genetics team suggests continuing medical management with high-calorie IV fluids. The family is concerned about invasive procedures. Evaluate the optimal management strategy.

A research study compares three siblings with homocystinuria: one responds to pyridoxine therapy, one responds to betaine, and one requires both treatments plus dietary restriction. All have elevated homocysteine but different methionine levels. Analyze which underlying molecular mechanism best explains the variable treatment responses among these siblings.

A 4-year-old boy presents with dark urine that turns black upon standing. His parents report that his diapers developed dark stains since infancy. Physical examination is otherwise normal. Urine analysis shows elevated homogentisic acid. What metabolic consequence is this patient at risk for developing in adulthood?

A newborn screening program detects elevated leucine levels in a 3-day-old infant who appears clinically normal. Confirmatory testing shows elevated branched-chain amino acids. The parents ask about immediate treatment versus watchful waiting given the infant's current stable condition. Synthesize the most appropriate counseling and management approach.

A 14-year-old boy with a history of intellectual disability presents to the emergency department with acute hemiparesis and altered mental status. He has ectopia lentis and marfanoid habitus. MRI shows acute ischemic stroke. Laboratory studies reveal elevated plasma homocysteine (180 μmol/L; normal <15) and methionine (65 μmol/L; normal 10-40). Genetic testing shows compound heterozygous mutations in CBS gene. Evaluate the most appropriate long-term management strategy.