PAH and phenylketonuria: Phenylketonuria (PKU; OMIM 261600) is an autosomal recessive disease, which results in a toxic excess of Phenylalanine (Phe) due to the loss of function of phenylalanine hydroxylase (PAH; EC 1.14.16.1) with an incidence of 1:15,000 live births [1].