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Phenylketonuria in Children

Medically reviewed by Last updated on May 6, 2024.

What is phenylketonuria (PKU)?

PKU is a condition that prevents your child's body from breaking down phenylalanine. Phenylalanine is a substance the body uses to make other proteins that are needed for normal growth. Phenylalanine is found in many foods, such as meat, poultry, fish, eggs, milk, cheese, beans, nuts, and seeds. When phenylalanine is not broken down properly, it builds up in the body. This can cause brain damage and lead to serious growth and learning problems.

What causes PKU?

PKU is caused by a defect in the gene that makes the enzyme needed to break down phenylalanine. The enzyme that breaks down phenylalanine may be present only in small amounts, or it may be absent. A child inherits PKU when both parents have the defective gene.

What are the signs and symptoms of PKU?

A child with PKU may look normal and completely healthy for the first few months of life. Signs and symptoms may appear between 3 to 6 months of age. Your child may be less active and develop more slowly than other children. He or she may lose interest in the things around him or her. Your child may also have any of the following:

How is PKU diagnosed?

How is PKU treated?

Treatment options

The following list of medications are related to or used in the treatment of this condition.

Call your local emergency number (911 in the US) if:

When should I call my child's pediatrician?

Care Agreement

You have the right to help plan your child's care. Learn about your child's health condition and how it may be treated. Discuss treatment options with your child's healthcare providers to decide what care you want for your child. The above information is an educational aid only. It is not intended as medical advice for individual conditions or treatments. Talk to your doctor, nurse or pharmacist before following any medical regimen to see if it is safe and effective for you.

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Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.