What Is Phenylketonuria (PKU)?

Phenylketonuria (PKU) is an inborn error of protein metabolism. It’s a rare disease, and children who are born with PKU inherit it from their parents.

PKU prevents the body from being able to properly break down proteins — specifically phenelalanine found in protein. This causes phenelalanine to build up in the blood and leads to problems throughout the body.

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

  • Behavioral or mental health problems.
  • Developmental delays.
  • Seizures.

A pregnant mother with PKU not controlled by diet may cause a more severe form of it in her baby.

This can cause birth defects, such as a small head (microcephaly) and heart problems.

You may not notice the effects in most children born with PKU until they’re a few months old.

The Center for Rare Disease Therapy (CRDT) at UPMC Children’s Hospital of Pittsburgh has experts who diagnose and treat PKU.

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 phenelalanine are high.

Phenylketonuria Symptoms and Diagnosis

PKU symptoms

Children have routine testing for PKU at birth. Unless a child is born with birth defects, symptoms of PKU may not become noticeable for a few months.

Symptoms of PKU 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.
  • Behavior problems.
  • Intellectual disability.
  • Memory problems

Diagnosing PKU

Your doctor will test your baby for PKU a day or two after birth. They will take a small amount of blood from your baby’s heel for this and other routine tests.

If the test shows that your baby may have PKU, your doctor will do additional tests. These may include another blood test, or a urine test.

PKU Treatment

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

The approach will depend on how severe your child's PKU is, or how high their blood levels are.

At the CRDT at Children’s, we treat PKU with the following options.

Low protein diet and formula

The first line of treatment for PKU may include a low-protein diet. Infants may need special formula to control the amount of protein they eat.

As your child grows older, they may need to use a formula supplement to make sure they’re getting enough protein.

Medicine and enzyme replacement therapy for PKU

Medications and enzyme replacement therapy may also be useful for treating PKU. They may help the body break down phenelalanine or tolerate it better.

Future PKU treatments

Although this treatment is not yet available, liver transplants may be a cure for PKU in the future.

PKU will require lifelong treatment and monitoring to prevent symptoms and complications until there’s a cure.

Jerry Vockley, MD, PhD

Director, Center for Rare Disease Therapy
Chief of Genetic and Genomic Medicine

Dr. Vockley is a world leader in inborn errors of metabolism treatment and research. He’ s also a founder of the North American Metabolic Academy.

Read an update on the phase 2 trial testing SYNB1618 to treat PKU. Dr. Vockley is the lead researcher on the study.

Your Child's Phenylketonuria Consult and Care: What to Expect

If doctors diagnosed your child with PKU, we want you to know you’re not alone.

The Center for Rare Disease Therapy is here to help. To make an appointment for your child or refer a patient for PKU care, contact us by:

Here’s what you can expect when you come to us for your child’s PKU consult.

What should I expect at my child’s first visit for PKU care?

Your first visit to the CRDT will take from 4 to 6 hours. Your child will receive a complete assessment from one of the center's doctors.

The doctor will make or confirm a PKU diagnosis and find out how much the disease has progressed.

Because we work as a team at the center, other doctors and staff might see your child during your visit.

These may include a:

  • Neurologist.
  • Heart specialist.
  • Surgeon.
  • Nutritionist.
  • Genetic counselor.
  • Psychologist.
  • Child development specialist.

What are the next steps after my child's PKU visit to the Center for Rare Disease Therapy?

Members of your child's care team will talk with you about:

  • Likely next steps for your child.
  • PKU treatment options.
  • Ways to help your child's quality of life at home.

By the end of your visit, you'll have a PKU care plan tailored to your child's needs. We'll also schedule a follow-up visit.

You'll meet our nurse practitioner. You can contact them by phone or video conference with any concerns before your next visit.

Before you leave, please ask us about your child's PKU, treatment, or anything else on your mind.

How long will I need to wait for my child's PKU test results?

We'll call within two weeks to review the test results and the next steps for your child's PKU care.

You can also find your child's test results if you have a MyCHP account — Children's patient portal.

MyCHP lets you manage your child's health online. It's free for kids getting treatment at UPMC Children's Hospital of Pittsburgh and their loved ones.

Partners in Your Child's Phenylketonuria Care

A child with a rare disease like PKU affects the whole family. We see each family member as our partner at the Center for Rare Disease Therapy.

The best care happens when we merge our PKU expertise with your knowledge of your child's needs.

Center for Rare Disease Therapy patient storiesMeet Our Rare Disease Center Patients

Learn how others are finding help and hope for their child’s rare disease through the expertise at UPMC Children’s.

View Center for Rare Disease Therapy patient stories »

Contact Us About Your Child’s PKU

At the CRDT, every child diagnosed with a rare disease receives a tailored treatment plan and family-centered care.

For an appointment, consult, or referral, contact us:

We’ll be in touch within 2 business days.