Phenylketonuria is the most common inborn error of amino acid metabolism. There is a broad continuum of phenotypes, and it is mainly due to phenylalanine hydroxylase deficiency. Without treatment, most children develop profound and irreversible intellectual disability, but even when treatment is started by 4 weeks of age, subtle defects in intelligence quotient, executive function, sustained attention, and reaction time occur. Traditionally, the mainstay of treatment is a low-phenylalanine diet, but newer treatment modalities are now being introduced or being clinically evaluated. These include BH4 supplements, large neutral amino acids, and PEGylated recombinant phenylalanine ammonia lyase (PEG-PAL) therapy.
MacDonald, A. (2013). Phenylketonuria. In Brenner’s Encyclopedia of Genetics: Second Edition (pp. 300–303). Elsevier Inc. https://doi.org/10.1016/B978-0-12-374984-0.01153-0