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Information about PKU

Understanding PKU and blood Phenylalanine (Phe) management  

PKU is an inherited disorder whereby the body fails to break down an amino acid called Phenylalanine (Phe) found in protein-rich food. Without appropriate management, the disorder causes irreversible damage to the developing brain in children. In adults and teenagers, it results in slow reaction times, poor concentration, poor memory and emotional instability leading to depression, anxiety and irritability.

This website provides information about the disorder and how to manage blood Phenylalanine (Phe) levels in everyday life. Select a category from the left of the screen to find out more about PKU management; read a guide to best practices; discover the way ahead and about the genetics.

Confirming a diagnosis: the Guthrie test  

The Guthrie or heel prick test is routinely carried out within days of a baby’s birth. A drop of blood is obtained from the baby’s heel and sent to a laboratory for analysis. If Phenylalanine (Phe) levels in the blood are high, your practitioner will arrange further tests to confirm the diagnosis.

The science of PKU: a medical explanation  

The body uses amino acids found in food containing protein to build muscle, provide energy and manufacture other chemicals. An enzyme called Phenylalanine Hydroxylase (PAH) and a cofactor or helper called Tetrahydrobiopterin (BH4) breaks down Phenylalanine (Phe) into Tyrosine (Tyr), which is used by the brain to send nerve signals around the body. Tyr is also required to make the skin pigment Melanin and the hormone Thyroxin

However in people with PKU, the PAH enzyme is deficient and Phe in the blood cannot be broken down. Over time, excess levels of Phe build up in the blood and begin to damage the brain.

As a result, blood Phe levels must be controlled and kept low. Discover more in this section about how to live with the disorder during specific stages of life.

Diagram explaining Phe mechanism in a healthy body and a PKU body

Information for women seeking to become pregnant

Learn about the importance of maintaining low blood Phe levels before and during pregnancy.


PKU treatment information

Keep up to date with treatment options to help manage blood Phe levels.


Manage your life with PKU

Useful tips to help you manage your everyday life.