A 2-day-old neonate develops jaundice, hepatomegaly, and cataracts. Urine reducing substances are positive but glucose oxidase test is negative, indicating a non-glucose reducing sugar in urine. The infant was being breastfed. Deficiency of which enzyme is most likely responsible?

• A Aldose reductase
• B UDP-glucose-4-epimerase
• C Glucose-6-phosphatase
• D Galactose-1-phosphate uridylyltransferase ✓

Explanation

Classical galactosemia results from deficiency of galactose-1-phosphate uridylyltransferase (GALT), causing accumulation of galactose-1-phosphate and galactitol. Galactose is a reducing sugar giving a positive Benedict's test, but it is not detected by glucose oxidase (which is glucose-specific). Galactitol accumulates in the lens, causing cataracts; galactose-1-phosphate accumulates in liver and brain, causing hepatomegaly and intellectual disability.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.