What is Phenylketonia (PKU)

Phenylketonuria is a rare metabolic disorder that affects the way the body breaks down protein. In particular, people with PKU cannot break down a substance in food called phenylalanine. As phenylalanine builds up in the blood, it can cause brain damage. However, early detection and intervention can prevent intellectual disability and result in normal growth and development.

What are the symptoms of PKU?

At first, there are often no symptoms in babies born with PKU. However, if left untreated, PKU can result in severe brain damage. Symptoms of PKU include:

  • Fair skin (from too much phenylalanine)
  • A musty body odor (from too much phenylalanine)
  • Head size significantly below normal
  • Delayed mental and social skills
  • Hyperactivity
  • Jerking movements of the arms or legs
  • Intellectual disability
  • Seizures
  • Skin rashes (eczema)
  • Tremors
  • Unusual positioning of hands

How is PKU treated?

PKU is a treatable disease. Treatment involves a diet that is extremely low in phenylalanine, particularly when the child is growing. Infants are typically given a special formula without phenylalanine. People with PKU must eat a protein-free diet, because nearly all proteins contain phenylalanine and avoid artificial sweeteners with aspertame, which also contains phenylalanine.

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