Phenylketonuria (PKU), or phenylalanine hydroxylase deficiency (PAHD), is a rare autosomal recessive disease, induced by the deficiency of the hepatic enzyme, phenylalanine hydroxylase (PAH) that converts the essential amino acid phenylalanine (PHE) into tyrosine (TYR) [1]. The gene discussed is PAH; the disease is phenylketonuria.