Mention causes and effects of phenylketonuria.

Explanation

The affected individuals lack an enzyme that catalyses the conversion of the amino acid phenylalanine in to tyrosine. Hence phenylalanine get accumulated and converted into phenyl pruvic acid and other derivatives. Accumulation of these chemicals in the brain results in mental retardation, these are also excreted in the urine as they are not absorbed by the kidney.