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Phenylketouria (PKU) is a metabolic disease due to the reduction or loss of activity of the enzyme phenylalanine hydroxylase (PAH). It is required to metabolise the amino acid phenylalanine to tyrosine and the impact of this deficiency can be severe causing mental retardation and organ damage. It is a fairly well known disease since it is one of several genetic disorders that babies are screened for at birth.[1] Neonatal screening for PKU is important since immediate changes in the diet can avert critical damage. The diet is designed to limit the intake of phenylalanine, as well as supplementing with tyrosine, and can reduce the severity of the symptoms allowing those with the disease to lead relatively normal lives.

PKU was the first disease to be systematically screened for in new born infants. The test was developed in 1961 by Robert Guthrie at the University of Buffalo Children’s Hospital and relied on the fact that excess phenylalanine is present in the blood of those with the disease.[2] By 1967 there were laws in thirty seven states in the U.S. that required all newborns to be screened for PKU.


  1. Newborn Screening Resources. National Newborn Screening & Genetics Center. 26 Jul 2007
  2. Guthrie, R. Blood Screening for Phenylketonuria. JAMA, 178:863. 1961.