Identify the statements which hold true for Phenylketonuria.

(A) Phenylketonuria is a sex linked disorder
(B) Phenylpyruvic acid is accumulated and converted to phenylalanine
(C) It is caused by mutation in a pleiotropic gene
(D) The affected individual lacks enzyme phenylalanine hydroxylase

Choose the correct answer from the options given below:

(C) and (D) only

The correct answer is Option (3) → (C) and (D) only

Phenylketonuria : This inborn error of metabolism is also inherited as the autosomal recessive trait. The affected individual lacks an enzyme that converts the amino acid phenylalanine into tyrosine. As a result of this phenylalanine is accumulated and converted into phenylpyruvic acid and other derivatives. Accumulation of these in brain results in mental retardation. These are also excreted through urine because of its poor absorption by kidney.

When a single gene can exhibit multiple phenotypic expression such a gene is called a pleiotropic gene. The underlying mechanism of pleiotropy in most cases is the effect of a gene on metabolic pathways which contribute towards different phenotypes. An example of this is the disease phenylketonuria, which occurs in humans. The disease is caused by mutation in the gene that codes for the enzyme phenyl alanine hydroxylase (single gene mutation). This manifests itself through phenotypic expression characterised by mental retardation and a reduction in hair and skin pigmentation.