Understanding Phenylketonuria

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The Understanding Blog series intends to give readers a general overview of the rare diseases Solace Nutrition offers Medical Foods and dietary supplements for. This time, we take an in-depth look at Phenylketonuria (fen-ul-key-toe-NU-ree-uh). 


What is Phenylketonuria? What causes it?

Phenylketonuria, also known as PKU, is an Inborn Error of Metabolism inherited from the individual’s parents. This genetic disorder is caused by a mutation in the PAH gene and results in a toxic buildup of the amino acids phenylalanine in the brain and blood. It is diagnosed from a blood test that usually reveals harmful levels of the Phe to tyrosine ratio. Newborns are screened for PKU within the first few days after being born. Those with PKU have problems breaking down phenylalanine (Phe) from the protein in food they eat.1

PKU was first discovered by Norwegian physician and biochemist Asbjørn Følling in 1934. Følling had been studying metabolic diseases when a former student of his reached out to him regarding his two children with intellectual disabilities. Følling was asked to examine them and find the root of the problem. The children exhibited many symptoms characteristic of what we now know as PKU, but at the time it was a mystery.  One symptom they both had was a a foul-smelling odor from their urine. After extensive testing, he concluded that the children had excess phenylpyruvic acid in the urine. This led to Følling testing other children across the countries with intellectual disabilities and finding a few that shared similar results in their urine tests.2 


Quick Facts

  • Cases vary from country to country. For example, the case rate in the United States is 1 in 10,000 births, while Turkey has had as high of a 1 in 2,600 births.3
  • Children with PKU who start treatment early in life and properly stick to it can go on to live with limited issues.
  • June 28th is International PKU Awareness Day. In the United States, National PKU Day is recognized on December 3rd. 


What are the symptoms of PKU?

Symptoms of PKU are usually not evident until the child is 6 months of age. It may start as the child seeming delayed and socially detached. It then tends to develop into physical symptoms such as a noticeable odor in the breath, skin or urine caused by too much phenylalanine in the body. Left untreated, PKU can result in seizures, behavioral problems and intellectual disabilities. Along with potential heart defects, microcephaly (abnormally small head) is also a common characteristic of this disease. Cases of PKU can range from mild to severe. Severe cases are referred to as Classical PKU.4


Treatment for PKU

Treatment usually consists of diet and medication. In terms of diet, it is crucial to avoid foods high in Phenylalanine (Phe), as this amino acid is found in most protein-heavy foods. Foods that are considered high in Phe include meat, dairy, eggs, nuts, grains and legumes.5 

In addition to dietary habits, sapropterin is a drug approved by the FDA to treat PKU, although it has shown only to be somewhat effective in reducing symptoms for certain individuals. Sapropterin is in a class of medications called cofactors. It works by helping the body to break down phenylalanine so it will not build up in the blood. Even with drug treatment, patients must continue to follow a low phenylalanine diet.6 

Solace Nutrition distributes three products currently available that assist in the dietary management of PKU. These include:


  • PreKUnil® is a Medical Food containing phenylalanine-free, large neutral amino acid (LNAA) tablets allowing individuals with proven PKU to follow a more flexible diet plan. PreKUnil® tablets are suitable for all types of Phenylketonuria (PKU), including late-diagnosed PKU and Hyperphenylalaninemia (HPA). Prekulab’s pioneering and advanced PreKUnil® LNAA tablets are clinically proven to reduce Phe transport across the blood-brain barrier (BBB) and has been successful for PKU patients for more than 30 years.
  • NeoPhe® LNAA Tablets is a Medical Food containing Phenylalanine-free, Large Neutral Amino Acids (LNAA). NeoPhe® includes a clinically proven combination of large neutral amino acids (LNAA). These amino acids block Phenylalanine at the gut level, resulting in lower blood Phenylalanine.
  • NeoPhe® LNAA Lemon-Flavored Powder is a Medical Food containing Phenylalanine-free, Large Neutral Amino Acids (LNAA). It provides double protection against Phe by stopping it from entering the brain and inhibiting its entry into the blood. NeoPhe® uses sizable neutral amino acids in its formulation.


These products must be used in conjunction with a PKU diet that contains other sources of protein, vitamins and minerals. Although there is no cure for PKU, treatment that begins at a young age has a better chance at being effective in reducing the more severe symptoms that characterize Classical PKU. Although there is still much work to do, gene therapy looks like a promising option for PKU treatment. 



Life with PKU can be a challenge for numerous reasons. However, there are resources and support networks that those with PKU may take advantage of. As individuals with PKU require maintaining a strict diet, low-protein recipes are a common resource offered by these organizations. Websites such as pku.com have a number of recipes that are PKU-friendly. Other organizations such as Children’s PKU Network, the National PKU Alliance and Canadian PKU and Allied Disorders provide resources and support for those with PKU, such as information and tips for managing the disorder. 



  1. Phenylketonuria – NORD (National Organization for Rare Disorders). (2021). Retrieved 4 August 2021, from https://rarediseases.org/rare-diseases/phenylketonuria/


  1. The Discovery of PKU. (2000). [Ebook]. Retrieved from https://depts.washington.edu/pku/PDFs2/DiscoveryofPKU.pdf


  1. El-Metwally, A., Yousef Al-Ahaidib, L., Ayman Sunqurah, A., Al-Surimi, K., Househ, 

M., Alshehri, A., Da’ar, O. B., Abdul Razzak, H., & AlOdaib, A. N. (2018). The Prevalence of Phenylketonuria in Arab Countries, Turkey, and Iran: A Systematic Review. BioMed Research International, 2018, 1–12. https://doi.org/10.1155/2018/7697210


  1. Phenylketonuria (PKU) – Symptoms and causes. (2021). Retrieved 4 August 2021, from https://www.mayoclinic.org/diseases-conditions/phenylketonuria/symptoms-causes/syc-20376302


  1. PKU- Friendly Recipes. (2021). Retrieved 4 August 2021, from https://www.pku.com/event-and-community/recipes

6. Sapropterin: MedlinePlus Drug Information. (2019). Retrieved 5 August 2021, from https://medlineplus.gov/druginfo/meds/a608020.html