A lot of things are celebrated in the month of February, but for me, one of the most important is celebrated on the last day of the month. February 28th (or 29th) is designated as Rare Disease Day, a day to raise awareness about rare diseases and improve access to treatment and medical representation. There are more than 6,000 identified rare diseases, and more than 300 million people worldwide are affected—equivalent to 5% of the world’s population.
One of these rare diseases is phenylketonuria, or PKU (previously discussed here). My son, Mason, was diagnosed with PKU through his newborn screen, and we began treatment for the condition when he was less than a week old.
But what exactly is PKU?
PKU is considered an inborn error of metabolism, which is a rare genetic disorder in which the body cannot properly turn food into energy due to a defect in a specific enzyme that helps break down parts of food. In the case of PKU, there’s a defect in the phenylalanine hydroxylase (PAH) enzyme responsible for breaking down the amino acid phenylalanine (Phe) and converting it to tyrosine.
PAH is found in the kidneys and the liver, and in people with PKU, it’s either non-functioning or only partially functional. This means that there’s either no or a slow breakdown of Phe, allowing levels of the amino acid to build up in the bloodstream and become toxic to the brain. Up until newborn testing was commonplace, individuals with PKU went undiagnosed until neurological symptoms began occurring, including hyperactivity, delayed intellectual development, and seizures. Most untreated PKU patients have difficulty or are unable to walk, talk, and feed themselves. Now that newborn testing can diagnose PKU, treatment can begin early, and although there are still other difficulties associated with treatment, individuals with PKU can live normal lives.
What does PKU treatment look like? It looks like a very strict diet, required medical formula, and frequent blood draws. It may also look like daily medication to help keep levels of Phe low in the blood.
Let’s break these down a bit further.
PKUers can’t break down phenylalanine, and thus, they need to avoid foods that have high levels of Phe; these foods include meats, dairy, tofu, soy, nuts, beans, and diet sodas, as well as, to some extent, pastas, grains, and baked goods (regular flour). Diet-wise, this means that people with PKU can eat a vegan diet but without tofu, soy, nut butters, pastas, and breads that vegans eat to make up for the protein they don’t get from eating meat and dairy.
But wait, don’t we all need protein to live? Yes, yes we do, and that obviously includes people with PKU. In order for PKUers to get the protein they need to grow and develop properly, they have to take a special formula. This formula contains all the amino acids needed for growth except for Phe, and a person with PKU has to take this for their entire life. There are different types of formulas for different ages as well as different forms of the formula—powder, liquid, tablets—so there’s at least some variety from which PKUers can choose, but they have to take it in some way to stay healthy.
And to ensure they’re staying healthy and that their Phe levels are staying in a safe range, they have to regularly do blood draws. In infants, draws are done every day or every other day until protein tolerance and the required levels of the medicated formula can be determined. Once those levels are established, draws can be done less often, usually weekly or biweekly, as long as levels are maintained within the treatment range. Infant draws are done via a heel prick and are switched to a finger prick about the time the child learns to walk. Alternately, draws can be done via a vein in the arm at any age. Like taking the medicated formula, blood draws must be done for life.
At this time, there is no cure for PKU, although there are several medical therapies that can ultimately help increase the amount of protein an individual with PKU can eat. Kuvan works by stimulating the PAH enzyme and helping break down Phe, while Palynziq serves as a substitute for PAH, allowing the body to break down Phe regardless of whether or not the body’s own PAH functions. Although both of these medications help treat PKU, the each have their pros and cons. Because some PKUers have completely non-functioning PAH, there’s no activity for Kuvan to stimulate, and those people thus can’t use Kuvan as a treatment. Palynziq works for anyone regardless of PAH functionality, but there’s a higher risk of a severe allergic reaction, so users must always carry around an EpiPen in case of an event.
By staying on diet and on formula—and taking medications as prescribed—people with PKU can live a happy and healthy life. Of course, some things about their life will look different than other peoples’, specifically their diet, but there are so many people today that require a specialized diet due to allergies or intolerances that a PKUer’s eating habits don’t seem so strange. Furthermore, increased awareness of PKU has led to the development of PKU-friendly menus or at least assistance in finding diet-appropriate foods. Walt Disney World is one such place where people with PKU (as well as various food allergies or other medically-restrictive diets) can get in touch ahead of a visit to get assistance with their dining choices.
There are also a number of ongoing clinical trials that would provide additional treatments or even a cure for PKU. There is hope that within the next few decades, if not sooner, PKU will be a rare but curable disease.
For more information about PKU, visit the National PKU Alliance. And if you know someone with PKU or are simply a kind, caring human being, please take a moment of your time to support the Medical Nutrition Equity Act which would ensure that insurance covers the formula and medicated foods required for people with PKU and other metabolic diseases to survive and live healthy lives. As a mother of an infant son with PKU, I would greatly appreciate your support.
Do you have more questions about PKU? Ask away in the comments below.
This is Rose and the information on PKU was very well written and helpful.