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About PKU

Phenylketonuria (PKU) is an inherited metabolic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase (PAH). This enzyme is required for the breakdown of phenylalanine (Phe), an amino acid found in all protein-containing foods. When PAH is deficient or defective, Phe accumulates to abnormally high levels in the blood.

Clinical manifestations of sustained high Phe levels include a variety of serious neurological and neuropsychological complications, including:

  • Intellectual disability and brain damage
  • Mood disturbances
  • Seizures and tremors
  • Cognitive problems
  • Executive function deficits


In the U.S., newborns are tested for PKU soon after birth as a part of the newborn screening program.


For people living with PKU, diet is first line management, including a low-protein diet and specially formulated Phe-free medical foods. When managing the diet it is important to keep the below in mind:

  1. Phenylalanine is a component of all natural protein. Milk and dairy products, meat, fish, chicken, eggs, beans and nuts contain high amounts of phenylalanine and must be excluded from the diet. Fruits, vegetables, and breads and pastas also contain Phe, but since the amount of Phe in these food are lower, small amounts may be able to be included in the diet.
  2. Phe-free medical foods provide necessary nutrients (e.g., tyrosine).

Image: Lab technician filling vial
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