With PKU, the foods you eat directly impact the way your brain functions.

What is PKU?

PKU is short for phenylketonuria, also known as PAH deficiency, which is a rare genetic condition that affects about 1 in 8,000 people in Europe. People affected by PKU have difficulty breaking down phenylalanine (Phe), an amino acid found in all natural protein.


Food impacts blood Phe levels.

The reason people with PKU can't break down Phe is that they have a problem with an enzyme called phenylalanine hydroxylase (PAH). PAH breaks down Phe into another amino acid called tyrosine.

Since Phe is found in many foods, such as chicken, meat, eggs, dairy, nuts, grains and beans, people with PKU typically eat a special diet.

Learn how you can prevent high blood Phe levels

PKU affects the brain.

The signalling molecules that brain cells use to communicate with each other are called neurotransmitters. When neurotransmitters are not made in the right amounts, the brain cannot function properly. High blood Phe levels can cause disruptions in neurotransmitters like serotonin and dopamine, which are important for mood, learning, memory and motivation.

In addition to disrupting neurotransmitter balance, Phe itself can be toxic to the brain. Scientists think that these changes are behind how high blood Phe affects the way a person thinks, feels and acts.


Symptoms of high blood Phe levels.

When Phe levels are high or uncontrolled, people with PKU can experience symptoms that have lasting effects on the brain. Symptoms of high or unstable blood Phe levels include:

  • Feeling "foggy" or a slowed processing of information
  • Behavioural or social problems
  • Problems with memory
  • Inattention
  • Difficulty in decision making, problem solving and planning
  • Depression
  • Anxiety
  • Irritability
Use the symptom diary to evaluate how PKU may be affecting you

PKU requires lifelong management.

It’s very important to start PKU management early and continue managing PKU for life. In most European countries, newborns are tested for PKU soon after birth as a part of national newborn screening programmes. PKU experts recommend beginning management as early as possible, starting management within the first 10 days of life. This helps protect an infant's developing brain from the damaging effects of high or unstable blood Phe levels.

“If I were to go back and talk to my 18-year-old self, I’d say, go back to clinic.”

- Keith, living with PKU for more
than 40 years

It wasn’t too long ago that medical experts thought PKU was a condition that was outgrown once the brain was fully developed. However, we now know that high blood Phe levels can be damaging at any stage of development, and that PKU must be managed for life. The brain never fully stops developing. Even those who have not been managing their PKU for many years may see an improvement in symptoms if they return to management. PKU experts recommend using every available option to control high or unstable blood Phe levels.

Review the most up-to-date protocols for PKU management
Check out the PKU
management guidelines.