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What Is PKU and How Is It Treated?

Reviewed on 2/11/2022
Newborn baby getting their foot pricked for a blood sample
PKU (phenylketonuria) is a blood disorder in which people have an absence or deficiency of an enzyme called phenylalanine hydroxylase (PAH) and therefore cannot break down the amino acid phenylalanine. PKU treatment usually involves a low-protein diet with no artificial sweeteners and amino acid supplements.

PKU (phenylketonuria) is a rare inherited blood disorder in which people are unable to break down the amino acid phenylalanine due to an absence or deficiency of an enzyme called phenylalanine hydroxylase (PAH).

  • If untreated, PKU can result in irreversible intellectual disability.
  • The mainstay of treatment for PKU is a carefully-controlled low phenylalanine diet.
  • Early diagnosis and the correct treatment including a properly maintained diet may prevent intellectual disability as well as neurological, behavioral, and dermatological problems. 

Diet & Treatment for PKU

  • A low-protein diet 
    • Avoid high-protein foods such as meat, fish, eggs, and dairy products
    • Control the intake of other foods, such as potatoes and cereals
    • Consume low-protein versions of common foods (such as flour, rice and pasta) specifically designed for people with PKU
  • Avoid aspartame, an artificial sweetener 
    • Food products that contain aspartame should be clearly labelled
    • Some medicines contain aspartame, such as some children's cold and flu remedies; medicines that contain aspartame are legally required to state it on the label 
    • Aspartame may be found in: 
      • Sugar substitutes such as artificial sweeteners used in tea and coffee  
      • Diet versions of carbonated drinks 
      • Chewing gum 
  • Amino acid supplementation

Regular blood tests to monitor phenylalanine levels are needed throughout a person’s life.

Most children with PKU are able to live healthy lives if properly treated.

What Are Symptoms of PKU?

When treatment is started early, PKU (phenylketonuria) may not cause any symptoms. If left untreated, PKU can cause damage to the brain and nervous system. 

Symptoms in untreated newborns not diagnosed in the first days of life may include: 

If PKU remains undiagnosed and untreated, symptoms may include:

  • Learning disabilities 
  • Behavioral problems such as frequent temper tantrums and episodes of self-harm
  • Eczema 
  • Frequent illness 
  • Jerking movements in arms and legs 
  • Abnormal muscle movements
  • Tight muscles
  • Increased reflexes
  • Involuntary movements
  • Tremors  
  • Seizures
  • Depression
  • Musty smell to breath, skin, and urine
  • Fairer skin, hair, and eyes than siblings who do not have the condition  

What Causes PKU?

  • PKU (phenylketonuria) is a genetic disorder in which a child inherits a genetic mutation from both parents, who are usually carriers and do not have any symptoms of the condition themselves.
  • A baby needs to receive two copies of the mutated gene to develop the condition: one each from their mother and father. 
  • If only one affected gene is passed on, a child will be a carrier of PKU.

How Is PKU Diagnosed?

  • PKU (phenylketonuria) is diagnosed during the first days of life via routine newborn screening. 
  • If PKU is confirmed, treatment is started right away to reduce the risk of serious complications. 

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Reviewed on 2/11/2022
References
Image Source: iStock Images

https://www.nhs.uk/conditions/phenylketonuria/

https://rarediseases.org/rare-diseases/phenylketonuria/