The person who is suffering from phenylketonuria lacks an enzyme that converts

Phenylketonuria is an inborn error of metabolism is also inherited as the autosomal recessive trait. The affected individual lacks an enzyme (phenyl alanine hydroxylase) that converts the amino acid phenylalanine into tyrosine. As a result of this phenylalanine is accumulated and converted into phenyl pyruvic acid and other derivatives. Accumulation of these in brain results in mental retardation.