Phenylketonuria, or PKU, is one of the most well-known conditions found through newborn screening. It is a rare, inherited metabolic disorder in which the body cannot properly break down phenylalanine, an amino acid found in protein. Without treatment, phenylalanine builds up in the blood and can cause intellectual disability, seizures, and developmental delays. With early detection and treatment, children with PKU can grow and develop normally, which is exactly why it is screened for.
What causes PKU
PKU is caused by changes (variants) in the PAH gene, which provides instructions for an enzyme called phenylalanine hydroxylase. This enzyme breaks down phenylalanine. When it does not work properly, phenylalanine accumulates. PKU is inherited in an autosomal recessive pattern, meaning a child must inherit a variant from both parents. It affects roughly 1 in 10,000 to 15,000 newborns in the United States.
How newborn screening detects PKU
PKU was the very first condition added to newborn screening in the 1960s, and it is included on every U.S. state panel today. The screen measures the level of phenylalanine in a few drops of blood from a heel prick taken in the first days of life. An elevated level prompts confirmatory testing. Because the screen is so well established, most cases are caught early.
How PKU is treated
PKU is highly manageable when caught early. The main treatment is a carefully controlled, low-phenylalanine diet, often combined with a special medical formula, and in some cases medication. Lifelong dietary management allows most people with PKU to live healthy lives. Early treatment, starting in the first weeks of life, is what prevents the serious complications.
How genetic screening fits in
State newborn screening does an excellent job of catching PKU. Genetic screening looks at the same picture from the DNA level and, in a single test, can also assess the genes tied to more than 1,000 other clinically actionable childhood conditions, many of which are not on any state panel. Fore Genomics offers an at-home cheek-swab screen, sequenced in CLIA-certified and CAP-accredited labs, with results supported by board-certified genetic counselors. See what we screen for or start screening.
Frequently asked questions
Is PKU on every state’s newborn screening panel?
Yes. PKU is screened for in all U.S. states and has been a core newborn screening condition for decades.
Can a child with PKU live a normal life?
With early diagnosis and consistent management of the low-phenylalanine diet, most people with PKU develop typically and live healthy lives.
Is PKU inherited?
Yes. PKU is autosomal recessive, so a child inherits a PAH gene variant from each parent. Parents are often unaffected carriers.
Medically reviewed by Fore’s Clinical Team. This article is for general educational purposes and is not medical advice. Sources: HRSA Newborn Screening; National Organization for Rare Disorders (NORD).