Phenylketonuria (PKU)

Young boy with brown hair and blue t-shirt

Picture courtesy of National PKU Alliance.

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For healthcare providers: Additional clinical information

PKU stands for phenylketonuria, a metabolic disease in which phenylalanine, which are parts of proteins, cannot be broken down.  It is an inherited metabolic condition usually diagnosed in the newborn period through screening in the hospital. 

About one in every 10-15,000 babies is born with PKU. 

People who have PKU do not have an enzyme to breakdown an amino acid called phenylalanine (PHE). PHE is found in food. When PHE builds up in body tissues, it can prevent normal brain development and can result in an intellectual disability. Early detection and treatment of PKU can prevent severe problems. 

PKU is treated with a special diet that must be followed closely in order for children to function well in school and life. Rigidly sticking to the PKU diet and formula is important during the critical period of development in early childhood. It remains necessary throughout adulthood. When children do not follow the diet, they usually do not become physically ill. However, they may have behavioral changes. They will not be able to think as well as when they are following the diet. 

Children with PKU do not have any distinct physical features. 

Note: There is wide variability within individuals who have this condition.

This information was last updated in May 2020.