Principles of Inheritance and Variation — BIOLOGY STD 12 Science — Question

→ It is an inborn error of metabolism.  
→ It is an autosomal recessive disease.
→ It is due to mutation of a gene that codes for the enzyme phenyl alanine hydroxylase.
→ This enzyme converts an amino acid phenylalanine into tyrosine.
→ The affected individual lacks this enzyme. As a result, phenylalanine accumulates and converts into phenyl pyruvic acid and other derivatives.
→ They accumulate in brain resulting in mental retardation. These are also excreted through urine because of poor absorption by kidney.