PAH and phenylketonuria: Phenylketonuria [PKU, MIM 261600, also referred to as phenylalanine hydroxylase (PAH; EC 1.14.16.1) deficiency] is a rare (prevalence < 1/10,000–1/15,000 births) autosomal recessive disorder characterized by an impairment of the body's ability to metabolize phenylalanine (Phe) [1].