Phenylketonuria (PKU) is a genetic disorder caused by a defect in the phenylalanine hydroxylase (PAH
) gene. PAH
is responsible for creating the enzyme that breaks down phenylalanine. Therefore, a mutation results in the buildup of phenylalanine in the body.
Newborns in the United States are screened for PKU immediately after birth, a move that helps to prevent major health issues. Still, some babies born with PKU may have heart problems, a small head, and a low birth weight For the duration of their lives, patients with PKU are required to follow a strict diet that limits phenylalanine, which is found mostly in foods that are high in protein. Failure to do so can lead to intellectual disability, seizures, behavioral problems, and mental disorders, among other issues..
The most severe form of PKU is classic PKU. These patients have even less function in their already faulty enzyme, leaving them at a higher risk for brain damage.
Signs and Symptoms
- Intellectual disability
- Delayed development
- Behavioral, emotional, and social issues
- Psychiatric disorders
- Neurological problems (may include seizures)
- Poor bone strength
- Skin rashes or eczema
- A musty odor in the child's breath, skin, or urine, the result of an excess of phenylalanine in the body
- Abnormally small head (microcephaly)
Since the 1960s, United States hospitals have regularly screened newborns for PKU. Tests are first conducted when the baby is 1 or 2 days old, with additional tests performed at 6 weeks to confirm initial results. If a child or adult exhibits signs of PKU, such as developmental delays, a blood test will be performed to evaluate a sample of the PAH
gene and the enzyme necessary to break down phenylalanine, either to confirm or deny the diagnosis.
Management of PKU consists primarily of restricting phenylalanine in the diet, which is often combined with tyrosine supplementation. Other fundamental amino acids are ingested via vitamins, mineral, and other micronutrients. A proper diet allows for regular development—both mentally and physically—and a somewhat normal life.
In addition to the requirements for amino acids, which are not significantly different from those of children, adults require the following:
- Calcium and vitamin D
- Folic acid
- Omega 3 essential fatty acids
Foods that contain large amounts of phenylalanine must be eliminated from the diet of a patient with PKU. These foods are typically high in protein and include:
- Milk and other dairy products
Because off-the-shelf infant formulas and breast milk both contain phenylalanine, babies with PKU need to consume a phenylalanine-free formula. Dietitians can estimate a careful amount of breast milk or regular formula to be combined with phenylalanine-free formula.
Children and adults with PKU can also drink a protein-substitute formula to ensure they receive all necessary essential nutrients. A doctor or dietician should assist the patient in choosing the most suitable formula.
The US Food and Drug Administration (FDA) approved sapropterin (Kuvan) to treat PKU. It increases tolerance to phenylalanine and is for use in combination with a PKU diet.
The transition from childhood to adulthood for a person with a chronic condition is often fraught with problems, and this is especially true for patients with PKU. A combination of money, age, and disease symptoms make it very easy for patients to fall behind on getting the proper and necessary treatment.
The cost of following a PKU diet can be extremely expensive, and it’s not likely to be covered by insurance companies when a 20-something adult changes to their own individual plan after being part of a family plan as a child. Additionally, the rebelliousness of teens and young adults means that many patients may get lost to follow-up. Stopping a treatment regimen does not always result in symptoms, however, when symptoms —such as behavioral or mild psychiatric problems— do appear, it is not difficult to make rational decisions on how to proceed and restart a proper diet.
All of these factors, and others, make it difficult for a patient with PKU to adhere to treatment.
The National PKU Alliance (npkua.org) was founded in 2008 by a collection of family members of patients with PKU across the country. It is the first national nonprofit organization that works to improve the lives of families and individuals associated with PKU through research, support, education, and advocacy, while ultimately seeking a cure.