Estimated occurrencePhenylketonuria (PKU) is an inherited congenital metabolic disorder. There is great variation in the incidence of PKU in different parts of the world. The incidence in Sweden is approximately 1 in 14,000 people. This means that in Sweden, about 5-7 children per year are born with PKU.
PKU is caused by changes (mutations) in the PAH gene which is located in the 12 (12q22-q24.2) chromosome. PKU leads to a deficiency or reduced function of phenylalanine hydroxylase enzyme, which is needed to convert phenylalanine amino acid to tyrosine amino acid. Phenylalanine is an essential amino acid that builds the body’s proteins. The functions of tyrosine include producing important neurotransmitters in the brain (noradrenaline, dopamine) and producing melanin pigment.
At birth, children with PKU have no symptoms. Untreated PKU leads to the development of high levels of phenylalanine which produces symptoms within a few months after birth. The symptoms may be mild to severe and include delayed development, impaired growth, microcephaly, intractable seizures, eczema, vomiting and a characteristic smell of the urine. These untreated patients will later develop intellectual disability (mild to severe), neuropsychiatric disabilities and motor difficulties. Patients often have light skin and hair due to tyrosine deficiency.
For patients who receive the diagnosis when they are older and whose treatment begins later, the difficulties vary greatly, both due to the level of intellectual disability (mild to severe) and to the level of difficulties with language and speech, motor skills, concentration, attention, eyesight and hearing, and development of epilepsy.
Phenylalanine is present in all foodstuffs that contain proteins and in the sweetener aspartame. Promptly started dietary treatment with suitable food and supplement of important amino acids will stop the development of symptoms and the child can develop normally. The dietary treatment consists of protein-poor food and supplement of important amino acids throughout life. Children are followed up regularly by means of blood tests.
PKU is discovered through voluntary newborn screening with a PKU test which is performed within 48 hours after delivery and was introduced in Sweden in 1965. Adopted children and children under the age of 18 that have immigrated to Sweden are also given the opportunity to take the PKU test.
Phenylketonuria, Følling’s disease, PKU
PKU causes a metabolic disturbance which may affect tooth development, and thus there is an increased risk of enamel defects. PKU-suitable food is rich in carbohydrates and often contains an increased sugar content which leads to an increased risk of developing dental caries. Dietary supplements with amino acids having low pH (sour) and frequent vomiting/acid reflux disease (GERD) cause an increased risk of dental erosion and enamel loss.
Advice on follow-up and treatment
- It is recommended to make early contact with a specialized dentist for information on how to best provide self-care and to offer enhanced preventive care as needed.
- Avoid aspartame since it partly consists of PKU-safe sweeteners include stevia, xylitol, sorbitol, saccharin and sucralose.
- In case of extensive dental erosion, consider installing a protective splint to limit dental wear.
- Tooth and bite development should be monitored. In case of abnormalities, an orthodontist should be contacted at an early stage for planning possible bite correction treatment