A neonate develops hemolytic anemia, jaundice, and cataracts within days of starting breastfeeding. Urine reducing substance test is positive but glucose oxidase test is negative. The enzyme most likely deficient in this infant catalyzes which reaction?

• A Galactose + ATP → Galactose-1-phosphate + ADP
• B UDP-galactose → UDP-glucose
• C Galactose-1-phosphate + UDP-glucose → Glucose-1-phosphate + UDP-galactose ✓
• D Galactitol → Galactose

Explanation

Classic galactosemia results from galactose-1-phosphate uridylyltransferase (GALT) deficiency, which catalyzes the exchange of galactose-1-phosphate with UDP-glucose to produce glucose-1-phosphate and UDP-galactose. Accumulation of galactose-1-phosphate causes hepatotoxicity, hemolysis, and intellectual disability; galactose also undergoes aldose reductase reduction to galactitol, which accumulates in the lens causing cataracts. The urine reduces Fehling solution (non-glucose reducing sugar) but is negative on glucose oxidase, distinguishing galactosuria from glucosuria.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.