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Phenylketonuria (PKU)

Also called: Phenylketonuria, PKU

An inherited condition where the body can't break down phenylalanine. Found on newborn screening and managed with a special diet for life.

Found byNewborn screening

Overview

The body can't break down phenylalanine, found in protein.

Newborn screening finds it early.

Symptoms

Common signs:

  • Found on newborn screen

Less common

  • Musty smell

When to get medical care

Call 911This isn't an emergency by itself. Call 911 for trouble breathing, chest pain, or fainting.
Get care todayNew or worse symptoms, or symptoms with fever.
See a doctor soonSymptoms that last or keep coming back.

Causes

Genes.

Does it spread or run in families?

  • It isn't contagious. You can't catch it from someone else.

Diagnosis

A clinician asks about your symptoms and may order tests.

The exam

A physical exam.

Tests

Tests, if needed:

  • Blood test:

Treatment

Treatment depends on the cause and how severe it is.

Self-care

  • Follow a low-phenylalanine diet
  • Avoid aspartame

Prevention

To lower your risk or prevent problems:

  • Newborn screening

Which doctor treats this

  • Start with your primary care provider (family doctor or internist).
  • They may send you to a medical geneticist (genetics doctor).

Living with it

  • Keep a simple diary of symptoms, triggers, and medicines to bring to visits.
  • Bring a list of your medicines and questions to each visit.
  • Stay active in ways that feel good to you.
  • Get enough sleep and manage stress.
  • Long-term illness can affect mood. Tell your doctor if you feel down or anxious.

Support groups and helplines

Back to school, work, or sports

  • Most people can keep working or going to school.
  • Ask about changes that help, like extra breaks or a flexible schedule. Workers may be covered by the ADA. Students may get a 504 plan.

Children, pregnancy, and older adults

  • Pregnancy: Strict diet control protects the baby.
  • Women with PKU: Strict diet before pregnancy.

Pregnancy and breastfeeding

  • If you're pregnant or planning to be, tell your prenatal provider about this condition.
  • Don't start or stop any medicine on your own. Some are safe in pregnancy and some need to be changed.
  • Ask before taking any pain reliever. The FDA advises avoiding ibuprofen and naproxen after 20 weeks unless your doctor says to.
  • Breastfeeding: Most medicines are fine, but ask. The NIH LactMed database lists what's known about each one.

For caregivers

  • Go to visits when you can and take notes.
  • Keep a list of medicines, allergies, and doctors in one place.
  • Learn the warning signs that need fast care.
  • Take breaks and ask for help. Caregivers need care too.

Outlook

Lifelong diet keeps the brain healthy.

Getting ready for your visit

Bring a list of your symptoms and medicines.

What to bring

  • A list of your medicines and supplements
  • Notes on when symptoms started and what makes them better or worse

Questions to ask

  • What's causing this?
  • What treatment do you recommend?

Research studies

Research studies test new ways to find and treat health problems. Some are looking for volunteers. Talk with your doctor before joining one.

Search ClinicalTrials.gov for studies on Phenylketonuria (PKU)

Sources

Last updated 2026-11-12.