A 6-month-old infant presents with recurrent hypoglycemia, failure to thrive, and cataracts. Urine shows reducing substance (non-glucose). The enzyme deficient in this condition also provides precursors for glycoprotein and glycolipid synthesis. Which enzyme is deficient?
- A Galactokinase
- B Galactose-1-phosphate uridylyltransferase (GALT) ✓
- C UDP-galactose-4-epimerase
- D Aldose reductase
Correct answer: B. Galactose-1-phosphate uridylyltransferase (GALT)
Explanation
Classic galactosemia results from GALT deficiency. Galactose-1-phosphate accumulates and is toxic to liver, brain, and lens. The cataracts result from galactitol (via aldose reductase) accumulating in the lens. Urine shows galactosuria (reducing but non-glucose). GALT normally generates UDP-galactose which is used for glycoprotein and glycolipid synthesis. Galactokinase deficiency causes only cataracts (galactose → galactitol pathway) without liver disease. UDP-galactose-4-epimerase deficiency is the mildest variant.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.