Question

Galactosemia is a congenital disease condition with absence of the enzyme _______________.

• A. Galactose-1-phosphate uridylyltransferase
• B. UDP-galactosyl transferase
• C. UDP-glucose pyrophosphorylase
• D. Beta-galactosidase

Hint:

Classic galactosemia is caused by a block at the second step of the Leloir pathway, which is catalyzed by the GALT enzyme. This leads to the accumulation of galactose-1-phosphate, the key toxic metabolite.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Galactosemia is an inherited autosomal recessive metabolic disorder characterized by the body's inability to metabolize galactose, a monosaccharide derived from the digestion of lactose.
Without proper metabolic breakdown, galactose and its phosphorylated intermediates accumulate in tissues, causing systemic damage.

Step 2: Detailed Explanation:
Galactose metabolism normally proceeds through the Leloir pathway:
- Galactose is first phosphorylated by galactokinase to yield Galactose-1-phosphate.
- In the next step, the enzyme Galactose-1-phosphate uridylyltransferase (GALT) catalyzes the conversion of Galactose-1-phosphate and UDP-Glucose into UDP-Galactose and Glucose-1-phosphate.
- Classic galactosemia (Type I), the most common and severe form of the disease, is caused by a congenital deficiency or complete absence of this GALT enzyme.
- This deficiency results in toxic accumulations of Galactose-1-phosphate and galactitol in vital organs, leading to liver damage, cataracts, cognitive deficits, and kidney failure if lactose is not excluded from the diet.
- Evaluating the other options:
- UDP-galactosyl transferase is involved in transferring galactose to acceptor molecules during glycoprotein synthesis.
- UDP-glucose pyrophosphorylase synthesizes UDP-glucose from glucose-1-phosphate and UTP.
- \(\beta\)-galactosidase is the enzyme responsible for hydrolyzing lactose into glucose and galactose in the digestive tract.

Step 3: Final Answer:
Galactosemia is caused by the absence of the enzyme galactose-1-phosphate uridylyltransferase.