Phenylketonuria is an inborn error of metabolism resulting from a deficiency of phenylalanine hydroxylase that is responsible for processing the essential amino acid phenylalanine and leads to elevated levels of phenylalanine and phenylalanine metabolites. PKU is inherited as an autosomal recessive trait. The mutation that causes PKU is located on chromosome 12. The specific type of mutation varies, resulting in variable severity in the clinical course of the disorder.
Newborn screening is very important for the diagnosis of this disease and has largely eliminated mental retardation caused by this disease.