What is Phenylketonuria (PKU)?

Phenylketonuria is an inborn error of protein metabolism. It is a rare disease, and children who are born with this condition inherit it from their parents. This condition prevents the body from being able to properly break down proteins — specifically phenylanine, which is found in protein. When the body is unable to break down certain proteins, phenylanine builds up in the blood and causes problems throughout the body.

Some ways that too much phenylanine can affect the body are:

  • Behavioral or mental health problems
  • Developmental delays
  • Seizures

If a pregnant mother has PKU that is not controlled by diet, her baby may have a more severe form of this disorder. This can cause birth defects in the baby, such as a small head (microcephaly) and heart problems.

In most children born with this disorder, the effects may not be noticed until the child is a few months old.

PKU Treatment

At Children’s Hospital of Pittsburgh of UPMC, we treat PKU with the following options:

  • Enzyme replacement therapy
  • Low protein diet
  • Formula
  • Medication

Types of PKU

There are four types of PKU:

  • Hyperphenylalaninemia: the lowest level above normal
  • Mild PKU: blood levels are mildly elevated
  • Moderate or variant: levels are not low but not high
  • Classic PKU: blood levels of phenylanine are high

Phenylketonuria Symptoms and Diagnosis

Phenylketonuria symptoms

Children are routinely tested for PKU at birth. Unless a child is born with birth defects, symptoms of PKU may not become noticeable for a few months. These symptoms in young babies can include:

  • Eczema, a skin rash
  • Seizures
  • Slow growth
  • A musty body odor or breath

Uncontrolled PKU can lead to other problems as the child grows, such as:

  • Developmental delays
  • Irritability
  • Behavioral problems
  • Intellectual disability
  • Problems with memory

Diagnosing PKU

Your baby will have been tested a day or two after birth. This test is done with a heel stick, and a small amount of blood is collected for this and other routine tests. If the test indicates that your baby may have this disorder, additional test will be performed. These may include another blood test, or a urine test.

PKU Treatment

If your child has this disorder, he or she will need to begin treatment as soon as possible. The goal of treatment is to keep blood levels of phenylanine low.

The treatment approach will depend on how severe your child's condition is, or how high the blood levels are.

The first line of treatment may include a low-protein diet. Infants may need special formula to control the amount of protein they eat. As your child grows older, he or she may need to use a formula supplement to ensure that they are getting enough protein.

Medications and enzyme replacement therapy may also be useful in helping the body to break down phenylanine, or to help the body tolerate it better.

Although this treatment is not yet available, in the future, liver transplants may be used to cure this disease. Until a cure is found, phenylketonuria will require lifelong treatment and monitoring to prevent symptoms and complications.

Contact Us

To make a referral, or to schedule an appointment for your child with the Center for Rare Disease Therapy, please call 412-692-7273 or send an email to rarecare@chp.edu.


Jerry Vockley, MD, PhD

Chief of Medical Genetics

Dr. Vockley is an international leader in treatment and research in medical genetics and the field of inborn errors of metabolism. He is also a founder of the North American Metabolic Academy.


What to Expect

If your child has been diagnosed with PKU, we want you to know that you are not alone – the Center for Rare Disease Therapy is here to help. Here’s what you can expect when you come to us for a consultation.

How quickly can we get an appointment?

At the Center for Rare Disease Therapy, a doctor specializing in genetic diseases can usually see a new patient within 1 to 2 weeks. To make an appointment, please call Jodie Vento at 412-692-7273 or send an email to rarecare@chp.edu.

How long should we expect our first visit with the doctor to take?

You can expect your first visit to take from 4 to 6 hours. Your child will receive a complete evaluation and may be seen by several doctors and other health care professionals.

What will happen during our first visit?

Your child will receive a complete evaluation to establish or confirm a precise diagnosis and determine how much the disease has affected the child. Because we work as a team at the Center for Rare Disease Therapy, during your visit your child may be seen by several doctors and other health care professionals, including a neurologist, a heart specialist, a surgeon, a nutritionist, a genetic counselor, a psychologist, and a specialist in child development.

We understand that the whole family is affected when a child has a rare disease. We see each family as our partner in caring for their child. We think the best approach to caring for a child with a rare disease emerges when we combine our depth of experience in rare diseases with your expertise in what’s best for your child.

We will talk with you about what we think is likely to happen with your child in the near future and about options we can suggest for treating and caring for your child. If surgery is an option for your child, we will help you understand what the surgery entails and what you may need to do to prepare for it. We will also talk with you about what you can do at home to care for your child and improve his or her quality of life. Please feel free to ask our specialists any questions you have about your child’s disease, treating and caring for your child, or anything else that is on your mind.

By the end of your visit, you will have a care plan tailored to your child’s needs and an appointment for a follow-up visit in 3 months. You will be introduced to our clinical nurse practitioner, who is available by phone or video conference to help you with any concerns you have between now and your next appointment.

How long might we have to wait for test results?

Depending upon the types of tests that the doctors order, you can expect to receive a phone call within 2 weeks to explain test results and discuss recommended next steps. Test results are also made available on Children's patient portal, myCHP, which is provided at no cost to patients, parents, and guardians.


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Contact Us

At the Center for Rare Disease Therapy, every child diagnosed with a rare disease receives an individualized treatment plan and family-centered care.

For an appointment, consultation, or patient referral with an expert at Children’s Hospital of Pittsburgh of UPMC for a child diagnosed with PKU, please contact:

Jodie Vento, MGC, LCGC
Phone: 412-692-7273
Email: RareCare@chp.edu

Clinical Studies

PKU Registry

PKUDOS - PKU Demographics, Outcomes, and Safety Registry

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PKU Retrospective Review

Burden of PAH Deficiency/PKU Among Adults: A Retrospective Chart Review and Cross-sectional Patient Survey

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