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Phenylketonuria (PKU)


The Manual's Editorial Staff

Last full review/revision Apr 2021| Content last modified Apr 2021
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What is phenylketonuria (PKU)?

Phenylketonuria is a hereditary metabolic disorder Overview of Hereditary Metabolic Disorders Your body breaks down food you eat into simple chemical building blocks. Then your body uses those building blocks to make other substances your body needs to grow and repair itself. This whole... read more . Children with PKU are born without the enzyme needed to break down phenylalanine. Phenylalanine is an amino acid (the building blocks of proteins) in many foods and drinks. Normally, your body breaks down and gets rid of extra phenylalanine. Children with PKU can't make the enzyme that is needed to break down phenylalanine to get rid of it.

What causes PKU?

Having 2 defective PKU genes causes PKU. If you have 2 defective PKU genes, you can't make an enzyme that breaks down phenylalanine.

  • PKU happens when both parents pass the gene that causes PKU to a child

  • If only one parent has the PKU gene and the other parent doesn't, the child can't have PKU

  • If both parents have the PKU gene, the child has a 1 in 4 chance of having PKU

What are the symptoms of PKU?

How can doctors tell if my child has PKU?

How do doctors treat PKU?

Starting in the first few weeks of a baby's life, the baby must go on a diet nearly free of phenylalanine. Doctors treat PKU with:

  • A strict diet that limits phenylalanine

  • Sometimes, medicine to increase tolerance of phenylalanine

People with PKU can't eat any milk, meat, or other foods with protein. They can have some fruits, vegetables, and grain cereals. They also eat special food, such as phenylalanine-free formula and nutritional products. Your child's doctor will tell you what your child can eat.

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