Question:medium
A 2-week-old baby presented with vomiting, acidosis and early cataract. Which of the following enzyme is defective?
A 2-week-old baby presented with vomiting, acidosis and early cataract. Which of the following enzyme is defective?
Show Hint
Vomiting + acidosis + hepatic illness + cataract in a milk-fed neonate = the severe (classic) form, not the cataract-only galactokinase form.
Updated On: Jun 22, 2026
- Galactose 1 Po4 uridyl transferase
- Galactokinase
- Hexokinase
- Aldol reductase
Show Solution
The Correct Option is A
Solution and Explanation
Pin down the syndrome. A two-week-old who, after taking milk, develops vomiting, acidosis, poor feeding and cataract is showing classic galactosemia. Milk lactose is split into glucose + galactose, so symptoms begin once milk feeding starts; toxic intermediates then damage multiple organs.
Which enzyme produces this severe form. The galactose pathway is: galactose -> (galactokinase) -> galactose-1-phosphate -> (GALT) -> UDP-galactose. The severe, life-threatening 'classic' galactosemia is due to loss of galactose-1-phosphate uridyltransferase (GALT). The galactose-1-phosphate that piles up behind the block is directly toxic to liver, kidney and brain, explaining the vomiting, acidosis, hepatomegaly and risk of E. coli sepsis.
The cataract link. Surplus galactose is reduced to galactitol by aldose reductase; galactitol osmotically swells the lens and forms an early cataract. So the cataract and the systemic toxicity together signal the transferase (GALT) defect.
Comparison of the choices.
- Galactokinase deficiency: only isolated cataract, no systemic toxicity - too mild for this baby.
- Hexokinase: a glycolytic enzyme for glucose, irrelevant here.
- Aldose ('aldol') reductase: it makes galactitol; it is overactive, not deficient - losing it would prevent cataract, not cause this illness.
Therefore the defective enzyme is Galactose-1-phosphate uridyltransferase (Option A).
Which enzyme produces this severe form. The galactose pathway is: galactose -> (galactokinase) -> galactose-1-phosphate -> (GALT) -> UDP-galactose. The severe, life-threatening 'classic' galactosemia is due to loss of galactose-1-phosphate uridyltransferase (GALT). The galactose-1-phosphate that piles up behind the block is directly toxic to liver, kidney and brain, explaining the vomiting, acidosis, hepatomegaly and risk of E. coli sepsis.
The cataract link. Surplus galactose is reduced to galactitol by aldose reductase; galactitol osmotically swells the lens and forms an early cataract. So the cataract and the systemic toxicity together signal the transferase (GALT) defect.
Comparison of the choices.
- Galactokinase deficiency: only isolated cataract, no systemic toxicity - too mild for this baby.
- Hexokinase: a glycolytic enzyme for glucose, irrelevant here.
- Aldose ('aldol') reductase: it makes galactitol; it is overactive, not deficient - losing it would prevent cataract, not cause this illness.
Therefore the defective enzyme is Galactose-1-phosphate uridyltransferase (Option A).
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