What is PKU?

Phenylketonuria (PKU) is a rare metabolic disorder that prevents the body from breaking down Phenylalanine, one of the amino acids found in protein. A person with PKU lacks the enzyme that normally converts Phenylalanine (Phe) to Tyrosine. Without it, Phe accumulates in the blood and acts as a toxin, putting them at risk of neurological complications, like: IQ loss, concentration problems, memory loss, seizures/tremors, and behavioral/mood disorders. If not treated in the first few months of life, PKU can even cause severe mental retardation.

In the US and many other countries, PKU is detected through mandatory newborn screening. The “heel-prick” test can help diagnose the disorder within days, and when treatment is started early (and adhered to diligently), affected children can expect to grow up normally, developing at the same rate as their PKU-free peers.

Treatment

Treatment comes in the form of a very strict diet that is low in Phe (and by association, protein). This doesn’t mean simply abstaining from high-protein foods like meat, fish, eggs, dairy, beans, nuts, etc…but requires precisely measuring all foods for their Phe content. A PKU-er does need some Phe (in very low amounts) for normal growth, and can get it in the form of fruits, vegetables and small amounts of starches. To get the protein missing from their diet, they must also drink a metabolic (Phe-free) formula multiple times per day.  

But what makes PKU treatment most challenging is that each patient’s tolerance of Phe is different. Diets are assigned to the individual and adjusted based on the results of regular blood tests. Working with a team of dietitians and doctors to assess the levels of Phe in the blood, adjustments are made to account for the natural tolerance changes that occur throughout life and development. In addition, the ability to break down Phe can be affected by external factors like exercise, illness, stress, and even fluctuations in routine. With so many variables at stake, management of the disorder is much more evaluative than it is prescriptive.

PKU & Pregnancy

Women who have PKU and wish to become pregnant must follow an even stricter “preconception” diet to ensure acute control of Phe-levels before and during pregnancy. High blood Phenylalanine levels can cause serious birth defects, while Phe levels that are too low may prevent intrauterine growth. But with control, healthy babies are being born to PKU mothers all over the world.

Advanced Therapies   

While there is still no cure, there have been exciting developments in new therapies. In 2007, Kuvan was developed as the first medication for PKU. It doesn’t work for all patients, but can dramatically increase the body’s ability to break down Phenylalanine, resulting in a more flexible diet and less risk of neurological symptoms. And as recently as May 2018, the FDA approved a new treatment for adults with PKU called Palynziq. Palynziq is administered through injection and is monitored closely due to a range of possibly severe side effects, but with success, it may replace the ineffective enzyme in PKU patients and provide the opportunity for an unrestricted diet. There are a number of other therapies in development, too. The future for PKU patients looks bright!   


 

PKU by the Numbers:

  • Most people with Classic PKU can only eat between 4 - 7 grams of protein per day.
    The average American (adult) eats between 65 - 100 grams of protein a day.

  • In the US, PKU occurs in 1 in 10,000 to 15,000 newborns.
    The NKPUA estimates there are currently 16,500 people living with PKU in the US.

  • In other countries, PKU is more common, occurring in some places as frequently as 1 in 4,500 births. Countries most affected are Ireland, Turkey, Poland, Iran, and the Czech Republic.

  • Almost 90% of people affected by PKU have blonde hair and blue eyes.
    …because phenylalanine is linked to melanin, the pigment responsible for hair and skin tone.

  • The average annual cost for the medical foods needed to treat PKU is $4,656.
    39 states have passed laws requiring at least some coverage of these foods, but coverage varies state-to-state (and plan-to-plan). Private insurance companies are currently exempt from these laws.

Sources:

  1. www.npkua.org

  2. pkunews.org/what-is-pku/

  3. www.mayoclinic.org/diseases- conditions/phenylketonuria/symptoms-causes/syc-20376302

  4. www.kuvan.com

  5. www.palynziq.com