This site is targeted at medical and radiology professionals, contains user contributed content, and material that may be confusing to a lay audience. Use of this site implies acceptance of our Terms of Use.


Dr Frank Gaillard et al.

Phenylketonuria (PKU) is an inborn error of metabolism resulting from abnormal metabolism of phenylalanine. If untreated, patients can develop central nervous system impairment. 


Phenylketonuria is inherited as an autosomal recessive disorder 1

Clinical presentation

Symptomatic patients demonstrate motor function impairment and mental retardation 1


Phenylkeonuria is due to deficiency of the hepatic enzyme phenylalanine hydoxylase which converts the amino acid phenylalanine, a large neurtal amino acid to tyrosine. The resultant accumulation phenylalanine in the blood competes for transport across the blood-brain barrier with other amino acids via the large neutral amino acid transporter. As a result the availability of other large neutral amino acids in neurons is decreased to the brain resulting in impaired neurotransmitter and protein synthesis 2

Treatment and prognosis

Treatment is with a phenylalanine restricted diet 3. Traditionally this has been enforced only during childhood, but recent evidence suggests life long dietary restriction is probably worthwhile [ref needed]. 

Related articles

Inborn errors of metabolism

Updating… Please wait.


Error Unable to process the form. Check for errors and try again.

Alert_accept Thank you for updating your details.