International PKU Day Date in the current year: June 28, 2025

Phenylalanine is an essential amino acid found naturally in the milk of mammals. Common dietary sources of phenylalanine include milk, eggs, chicken, beef, liver, soybeans, fish, seafood, and foods containing the artificial sweetener aspartame. Phenylalanine plays a critical role as a precursor for several neurotransmitters and the pigment melanin.

The enzyme phenylalanine hydroxylase, encoded by the PAH gene, metabolizes excess phenylalanine in the body. Mutations in this gene can render the enzyme inefficient or nonfunctional, resulting in a buildup of phenylalanine. The genetic condition characterized by decreased phenylalanine metabolism is called phenylketonuria (PKU).

A buildup of phenylalanine can cause seizures, behavioral problems, mental health disorders, and intellectual disability. It may also result in lighter skin and hair because phenylalanine is not properly converted into melanin, as well as a musty smell in sweat and urine. Children with untreated PKU are also more prone to chronic ischemic heart disease, asthma, diabetes, gastroenteritis, and some other conditions.

PKU symptoms do not present immediately after birth because the mother’s body breaks down phenylalanine during pregnancy, and it takes time for phenylalanine levels to rise. For this reason, newborns should be screened for PKU at birth so that treatment can begin as soon as possible to prevent irreversible brain damage. In many countries, PKU screening is obligatory as part of national newborn screening programs.

There is no cure for PKU, but it can be successfully managed with a low-phenylalanine diet and dietary supplements. The PKU diet restricts or eliminates foods high in phenylalanine. The diet is usually developed for each patient individually, depending on their remaining enzyme function and tolerable levels of phenylalanine. Dietary supplements are necessary to provide nutrients lacking in the low-phenylalanine diet.

To prevent severe intellectual disability, the diet must be started within the first two weeks of life. Patients with PKU who are diagnosed early and adhere to the diet usually do not exhibit symptoms and live normal lifespans.

International PKU Day was established in 2013 by the European Society for Phenylketonuria and Allied Disorders Treated as Phenylketonuria (E.S.PKU), an umbrella organization representing more than three dozen national and regional patient organizations in Europe.

June 28 was chosen as the date for International PKU Day because it is the birthday of both Horst Bickel and Robert Guthrie. Bickel, a German physician, helped create a low-phenylalanine diet for the treatment of PKU. Guthrie, an American microbiologist, developed a simple method of screening newborns for PKU.

Events and activities for International PKU Day are organized by the E.S.PKU, its member organizations, other regional, national, and international healthcare organizations, healthcare providers, public bodies, food producers, and individuals, such as patients and their families.