Which disease is caused by deficiency of galactose-1-phosphate uridyltransferase?

• A. Classic galactosemia
• B. Phenylketonuria
• C. Maple syrup urine disease
• D. Galactokinase deficiency

Answer: (A)

The key idea is that this enzyme deficiency disrupts the Leloir pathway’s step that normally converts galactose-1-phosphate and UDP-glucose into UDP-galactose and glucose-1-phosphate. When galactose-1-phosphate uridyltransferase is missing or severely deficient, galactose-1-phosphate and galactose accumulate in tissues, leading to toxic effects in the liver, kidneys, and brain. Clinically, newborns present with poor feeding, jaundice, liver enlargement, vomiting, and failure to thrive; without early dietary treatment, there’s a high risk of liver damage, cataracts later on, and potential developmental problems. Management focuses on eliminating lactose and galactose from the diet to prevent accumulation.

Other listed disorders involve different enzyme defects: phenylketonuria is due to phenylalanine hydroxylase deficiency; maple syrup urine disease arises from defects in the branched-chain α-ketoacid dehydrogenase complex; galactokinase deficiency causes galactose buildup with typically cataract formation but less severe liver involvement.