What is the cause of phenylketonuria? Write symptoms.

Explanation

Phenylketonuria is an inbom genetic disorder in which, the homozygous recessive individual lacks the phenylalanine hydroxylase needed to change the amino acid, phenylalanine to 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. Lack of the enzymes is due to the abnormal autosomal recessive gene on chromosome 12.