Phenylketonuria (PKU) (OMIM 261600) is an inherited, autosomal recessive metabolic disorder, caused by reduced conversion of phenylalanine (Phe) to tyrosine (Tyr), due to deficient phenylalanine hydroxylase (PAH) activity, resulting in increased blood Phe levels [1–4]. This evidence concerns the gene PAH and phenylketonuria.