Draft — awaiting clinical review

Phenylketonuria (PKU)

In plain words: The body can't break down phenylalanine, a building block found in protein. Lifelong care from a metabolic team keeps levels in a safe range.

Your genetics may influence your health, but they do not determine your worth. Understanding your body creates opportunities for informed care—not blame.

Designed to Heal provides general educational information and personal wellness tools. It does not diagnose genetic conditions, interpret genetic tests, or replace qualified medical care. Genetic disorders may require specialized diets, medication, monitoring, or other medical treatments. Consult a qualified healthcare professional before changing your treatment, nutrition, or exercise plan.

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We do not diagnose, interpret genetic tests or calculate risk. For testing or family-planning questions, ask your clinician about a certified genetic counselor.

1. Overview

PKU is an inherited condition in which phenylalanine (Phe) builds up in the body. Without treatment, high levels can harm the brain. Most babies in the U.S. are identified through newborn screening.

2. Genetic cause and inheritance

Caused by changes in the PAH gene. It is autosomal recessive: a person inherits one changed copy from each parent. Parents who each carry one copy usually have no symptoms.

3. Symptoms and complications

Without treatment: developmental delay and intellectual disability
Seizures, behavior or mood changes
A musty body odor, eczema, lighter skin and hair
In adults with high levels: trouble concentrating, anxiety or low mood

4. How clinicians diagnose it

Usually found by newborn blood screening, then confirmed with blood Phe tests and genetic testing by specialists.

5. Established medical treatment

A lifelong Phe-restricted diet with medical formula, planned by a metabolic dietitian
Regular blood Phe monitoring
Some people may be prescribed medication by their specialist
Special planning before and during pregnancy

6. Nutrition considerations

The PKU diet is a medical treatment, not a lifestyle choice — it is individualized by a metabolic team. Many high-protein foods and the sweetener aspartame contain Phe. Do not change protein intake or formula without your team.

Nutrition, movement and other supportive practices may support overall health, but they cannot change the inherited genetic variant.

7. Activity considerations

Physical activity is generally encouraged. Ask your metabolic team about fueling for long or intense exercise, since diet planning affects energy.

8. Safety precautions

Never stop or loosen the diet on your own — Phe levels can rise without obvious symptoms
Check labels for aspartame (it contains phenylalanine)
Plan pregnancy with your metabolic team well in advance — high Phe can harm a developing baby

9. Questions to ask your clinician

What is my target Phe range, and how often should I test?
How should my diet change during illness, growth or pregnancy?
Is medication an option for me?

10. References

Last updated October 8, 2026