Which one of the following genetic diseases is a result of inborn error of metabolism?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Phenylketonuria
An inborn error of metabolism is a genetic disorder in which a faulty gene leaves one enzyme missing or not working, so one step of a metabolic pathway breaks down. In phenylketonuria (PKU) the person lacks the enzyme that converts the amino acid phenylalanine into tyrosine. Phenylalanine piles up and is changed into phenylpyruvic acid and other products. These collect in the brain and cause mental retardation, and they are also passed out in urine.
(1) Haemophilia — Incorrect. It is a sex-linked recessive disease. A protein needed for blood clotting is not made properly, so even a small cut bleeds for long.
(2) Sickle-cell anaemia — Incorrect. It is an autosome-linked recessive disease. One base change in the beta globin gene (GAG to GUG) puts valine in place of glutamic acid, so the haemoglobin molecule changes its shape. It is a fault in a protein, and it is not called an inborn error of metabolism.
(3) Thalassemia — Incorrect. It is an autosome-linked recessive blood disease. Too little of the alpha or the beta globin chain is made, so the haemoglobin is low.
(4) Phenylketonuria — Correct. This is the disease that NCERT calls an inborn error of metabolism.
NCERT Extract:
Mendelian Disorders – …
