In the context of galactosemia as described, which enzyme deficiency is cited as absent?

• A. Galactokinase
• B. Galactose-1-phosphate uridyltransferase
• C. Lactase
• D. Glucokinase

Answer: (A)

Galactose metabolism starts with a step that traps galactose by adding a phosphate group, turning it into galactose-1-phosphate. If this first enzyme is missing, galactose cannot enter the normal pathway, so free galactose accumulates. The excess galactose is then diverted by other enzymes to galactitol, which can build up in tissues such as the lens and lead to cataracts. This pattern explains why the described scenario points to the absence of galactokinase: the defect is at the initial phosphorylation step, before galactose-1-phosphate is formed.

In contrast, lactose intolerance due to lactase deficiency involves the gut enzyme that breaks down lactose into glucose and galactose and does not produce the systemic features of galactosemia. Glucokinase acts on glucose, not galactose, so it wouldn’t be the missing enzyme in galactose metabolism. And deficiency of galactose-1-phosphate uridyltransferase causes classic galactosemia with a different, typically more severe set of manifestations, due to buildup of galactose-1-phosphate rather than free galactose.