Phenylketonuria In Children

What is phenylketonuria?

Phenylketonuria (fen-il-ke-to-NU-re-ah) , also called PKU, is an inherited condition where the body cannot break down certain foods. Normally, the liver makes many enzymes (proteins) that break down substances, such as phenylalanine. Phenylalanine is important for making other proteins, which are needed for normal growth. It is found in many foods, such as meat, poultry, fish, eggs, milk, cheese, beans, nuts, and seeds. With PKU, the enzyme that breaks down phenylalanine may be present only in small amounts or none at all. Phenylalanine may build up in the body and cause brain damage. This may lead to serious growth and learning problems, such as mental retardation.

What causes phenylketonuria?

Phenylketonuria is caused by a defect in the gene that makes the enzyme phenylalanine hydroxylase (PAH). A gene contains the information needed to make a certain substance. For a child to inherit PKU, both parents must have the defective gene. If the child gets only one defective gene, he may only be a PKU carrier. A carrier is usually not affected in any way.

What are the signs and symptoms of phenylketonuria?

A child with PKU may look normal and completely healthy for the first few months of life. If left untreated, signs and symptoms may appear between 3 to 6 months of age. Your child may begin to be less active and do things later than other children. He may lose interest or not pay attention to things around him. He may also have one or more of the following:

  • Learning, speech, or behavior problems.

  • More irritable, fussy, or restless than normal.

  • Musty or mousy odor of his breath, hair, skin, or urine.

  • Fair skin.

  • Short stature (height) or small head.

  • Skin may be dry or have rashes, such as eczema.

  • Vomiting (throwing up), muscle stiffness, or seizures (convulsions).

How is phenylketonuria diagnosed?

Your child may have one or more of the following:

  • Blood tests: A newborn screening test is usually done during your child's first days of life. A sample of your child's blood is taken and sent to the lab. This helps your child's caregiver learn if your child is at risk of having PKU or other genetic disorders. Other blood tests may be needed if the PKU screening is positive.

  • CT scan: This test is also called a CAT scan. An x-ray and computer are used to take pictures of your child's body. Your child may be given dye, also called contrast, before the test. Tell the caregiver if your child is allergic to dye, iodine, or seafood.

  • Genetic tests: Genetic testing may be needed to check your child's genes. This test helps caregivers learn how your child's genes may affect him. This may also help your child's caregivers decide on a treatment plan.

  • Magnetic resonance imaging scan: This test is also called an MRI. During the MRI, pictures are taken of your child's head. An MRI may be used to look at the brain, muscles, joints, bones, or blood vessels. Your child will need to lie still during an MRI. Never enter the MRI room with an oxygen tank, watch, or any other metal objects. This can cause serious injury. Tell your child's caregiver if your child has any metal implants in his body.

  • Urine tests: A sample of your child's urine may be collected and sent to a lab for tests. These tests help diagnose PKU and other disorders your child may have.

How is phenylketonuria treated?

Your child may need one or more of the following:

  • Diet: A special diet is needed to keep the amount of phenylalanine in the body low. This diet is different from one child to another. It is started as early as the first few days of life or a few weeks after birth. This special diet may need to be followed for life.

  • Medicines: Your child may be given medicines to treat his symptoms. Medicines may be given to treat his rash, vomiting, to control his seizures, or to relax his muscles.

  • Special formulas or products: These are also called protein substitutes that have little or no phenylalanine. These formulas have the right amino acids, calories, vitamins, and minerals your child needs. Ask your child's caregiver for more information about these special formulas.
With treatment, such as medicines and proper diet, your child may grow normally and serious health problems may be prevented.

Where can I get support and more information?

Phenylketonuria is a life-changing disorder for your child and your family. Accepting that your child has PKU is hard. You and those close to you may feel guilty, angry, depressed, or frightened. As parents, you may blame yourself and think you have done something wrong. These are normal feelings. Talk to your caregivers, family, or friends about your feelings. You may also want to join a PKU support group. This is a group of people who have PKU or have a child with PKU. Contact the following for more information:

  • Children's PKU Network
    3790 Via De La Valle, Ste. 120
    Del Mar , CA 92014
    Phone: 1- 858 - 509-0767
    Web Address:
  • March of Dimes Birth Defects Foundation
    1275 Mamaroneck Avenue
    White Plains , NY 10605
    Web Address:
  • National PKU News
    6869 Woodlawn Avenue NE, #116
    Seattle , WA 98115-5469
    Phone: 1- 206 - 525-8140
    Web Address:

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 caregivers 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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