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Non-PKU hyperphenylalaninemia

(Non • PKU • hie-puhr-fen-uhl-AH-luh-nih-NEE-mee-uh)

General Condition Information

Other Names

  • Benign hyperphenylalaninemia
  • Benign hyperphenylalaninemia (due to phenylalanine hydroxylase deficiency, GTP cyclohydrolase I deficiency, pterin-4-alpha carbinolamine dehydratase deficiency, and 6-pyruboyltetahydropterin synthase deficiency)
  • Benign hyperphenylalaninemia defect
  • Hyperphenylalaninemia

Condition Type

Birth Prevalence

  • The prevalence of this condition is currently unknown. It is a very rare condition. 

Screening Finding

High levels of phenylalanine

What is Non-PKU hyperphenylalaninemia

Non-PKU hyperphenylalaninemia, also called variant phenylketonuria, is an inherited (genetic) condition that prevents the body from processing proteins correctly. Your body breaks down the protein that you eat into parts called amino acids. Your body then uses those amino acids to make other proteins that it needs to function.

There are different forms of hyperphenylalaninemia (also called phenylketonuria). All the forms result in high levels of an amino acid called phenylalanine in the body.

In hyperphenylalaninemia, an enzyme called phenylalanine hydroxylase (PAH) is not made correctly. This enzyme helps change phenylalanine into other amino acids that your body needs.

When PAH is missing or severely damaged, phenylalanine cannot be processed. This more severe version of hyperphenylalaninemia is called classic phenylketonuria or PKU. When the enzyme PAH is made incorrectly but can still process some phenylalanine, this version is called non-PKU hyperphenylalaninemia. Non-PKU hyperphenylalaninemia has milder signs and symptoms compared to classic PKU.

Newborn Screening and Follow-Up

Condition Details

Treatment and Management

Most babies with non-PKU hyperphenylalaninemia do not require any treatment.

Some individuals with more severe forms of non-PKU hyperphenylalaninemia might need treatment. The goal of treatment is to prevent the health problems caused by this condition. It is important to talk to your health care provider about which treatment(s) are best for your baby. Treatments may include the following:

  • Restricted diet low in foods that contain phenylalanine
  • Special phenylalanine-free formula
  • Medications that contain a substance called BH4 that helps the body process phenylalanine

Children with non-PKU hyperphenylalaninemia have healthy growth and development.

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