Question

Identify the disease which is an inborn error of metabolism and is also inherited as the autosomal recessive trait.

• A. Thalassemia
• B. Haemophilia
• C. Down syndrome
• D. Phenylketonuria

Hint:

PKU lacks the enzyme phenylalanine hydroxylase and needs two mutant autosomal alleles.

Answer 1

The Correct Option is D

Step 1: Understand the question:
An inborn error of metabolism is a genetic defect in one enzyme of a metabolic pathway. We need the one that is also autosomal recessive.

Step 2: Check Phenylketonuria:
PKU is caused by a mutation in the gene for phenylalanine hydroxylase on an autosome. The enzyme cannot change phenylalanine into tyrosine.
It shows only when both alleles are mutant, so it is autosomal recessive. It is a classic inborn error of metabolism. So (D) is correct.

Step 3: Check the other options:
Thalassemia is autosomal recessive, but it is a defect in making globin chains of haemoglobin, not a metabolic enzyme defect.
Haemophilia is X-linked recessive, so it is not autosomal.
Down syndrome is a chromosomal disorder caused by trisomy of chromosome 21, not a single gene defect.

Final Answer:
Option (D), Phenylketonuria.