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Only 1 in 10 people surveyed are aware of PKU!12

Phenylketonuria (PKU) is a rare, lifelong metabolic condition which limits a person’s ability to break down protein, which may lead to cumulative toxic effects on the brain1.

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

Photo of green veg on dark kitchen surface

People with PKU have a problem with the phenylalanine hydroxylase (PAH) enzyme, and so can’t fully break down an amino acid called Phenylalanine (Phe), which is found in all protein-containing foods (e.g. nuts, meat, eggs, dairy) and sweeteners such as aspartame1.

If too much protein is consumed, high levels of Phe build-up in a person’s blood and disrupt the balance of neurotransmitters – or even cause physical damage to the brain itself. This can result in neurological symptoms such as problems with memory and attention, depression and anxiety2.

The condition is screened for during the new-born heel prick test, and affects around 1 in 10,000 people in Europe1,3

new-born heel prick test

PKU is an inherited autosomal recessive disease. This means that if both parents are carriers of the defective PKU gene, their baby has a 1 in 4 chance of suffering from PKU4. The condition is tested for in almost all European countries during the new born heel prick test, but general awareness of the condition remains low.

There is currently no cure for PKU, and management should be lifelong.

Until fairly recently, doctors thought that PKU was a condition that was outgrown once the brain fully developed as a teenager. However, we now know that high blood Phe levels continue to result in damage at any age, and so the condition should be managed for life5.

A heavily restricted diet and/or medical treatment is needed to keep Phe levels under control, but can place a huge burden on adults – impacting quality of life, personal relationships, and contributing to anxiety, stress and depression6,7.

Woman reading product label in grocery store

You can find out more about PKU in children, teens and adults by clicking the links below

diagnosed with PKU

Teens and young adults
growing up with PKU

living with PKU

The impact of untreated or poorly managed PKU can be severe

High or unstable blood Phe levels can lead to8,9:

  • Slow processing of information
  • Behavioral or social problems
  • Intellectual disability
  • Problems with memory
  • Seizures and tremors
  • Inattention
  • Anxiety, depression and irritability

People with PKU also face a high number of physical co-morbidities, including obesity, renal insufficiency with hypertension, and osteoporosis10.

Adults with PKU often face a difficult cycle of dietary management

Adhering to the diet required to control Phe levels requires careful planning. But the neurocognitive effects of PKU itself can make this even more difficult. And this is exacerbated even more by poor adherence to the diet – creating a vicious cycle for PKU patients7,9.

After the age of 18, it is common for people’s control of their PKU to decrease. This is likely due to a number of factors, including busy lifestyles, difficulties finding PKU-suitable food when socialising, and fewer specialist centres for adults11.

Even if people with PKU are able to strictly adhere to the diet, this can have a negative impact on other areas of their lives, with 34% reporting relationship difficulties with friends, family or partners, and 44% experiencing social exclusion7.

Find out more about what the Live Unlimited PKU campaign is doing to support change here.


  1. Wegberg AMJ, MacDonald A, Ahring K, et al. The complete European guidelines on phenylketonuria: diagnosis and treatment. Orphanet J Rare Dis. 2017;12(1):162. Published 2017 Oct 12. doi:10.1186/s13023-017-0685-2.
  2. Bilder DA et Al. Systematic Review and Meta-Analysis of Neuropsychiatric Symptoms and Executive Functioning in Adults With Phenylketonuria. Dev Neuropsychol. 2016 May-Jun;41(4):245-260.
  3. Pitt, J. Newborn Screening. Clin Biochem Rev. 2010 May; 31(2): 57–68.
  4. NORD. 2019. Phenylketonuria. Available at: Last accessed April 2019
  5. Berry et Al. Newborn screening 50 years later: access issues faced by adults with PKU. Genetics in Medicine volume 15, pages591–599 (2013)
  6. Al Hafid N, Christodoulou J. Phenylketonuria: a review of current and future treatments. Transl Pediatr. 2015;4(4):304–317. doi:10.3978/j.issn.2224-4336.2015.10.07
  7. Ford, S. et Al. Living with Phenylketonuria: Lessons from the PKU community. Molecular Genetics and Metabolism Report. 2018
  8. BioMarin Pharmaceuticals. 2017.Phe In The Brain | PKU. Phenylketonuria (PKU) Information [ONLINE]. Available at: . Last accessed: April 2019
  9. BioMarin Pharmaceuticals. 2019. PKU. [ONLINE] Available at: diseases/pku Last accessed: April 2019
  10. Burton, B., Jones, K., Cederbaum, S., Rohr, F., Waisbren, S., Irwin, D., Kim, G., Lilienstein, J., Alvarez, I., Jurecki, E. and Levy, H. (2018). Prevalence of comorbid conditions among adult patients diagnosed with phenylketonuria. Molecular Genetics and Metabolism, 125(3), pp.228-234.
  11. Cazzorla C et Al. Living with phenylketonuria in adulthood: The PKU ATTITUDE study. Molecular Genetics and Metabolism Reports 16 (2018) 39–45
  12. BioMarin commissioned polling company Alligator to conduct a six-question online survey amongst nationally representative samples from the UK, France, Germany, Italy, Spain, Sweden, The Netherlands and Turkey, with 4,151 total respondents in total.* The survey was completed between 1st and 6th June 2019. Respondents were asked to rate six life milestones on a 5 point scale from ‘Not at all’ stressful to ‘extremely’ stressful. Total number of respondents with an underlying health condition: 1,932. A total of 130 PKU patients were collected separately in partnership with patient groups in Italy, Sweden, Spain, Turkey, and The Netherlands.