Phenylketonuria

(PKU)

What is PKU?

PKU is a metabolic disorder that affects the way the body breaks down proteins. PKU is caused by a mutation in a gene that occurs on chromosome 12. The gene codes a protein called phenylalanine hydroxylase, which is an enzyme in the liver. Phenylalanine hydroylase breaks down the amino acid phenylalanine into other products the body needs. The shape of the enzyme changes when the gene is mutated and is unable to properly break down phenylalanine. Then phenylalanine builds up in the blood and poisons the nerve cells in the brain.


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What are the symptoms of PKU?

If a baby is born diagnosed with PKU there are usually no symptoms at first. If the baby is not treated for the disorder the symptoms could be severe brain damage, behavioral problems, and could stunt the growth of the baby. Other symptoms could be a small head or fair skin.


How do people get PKU?

Phenylketonuria is an autosomal recessive disorder. In order to have the symptoms of this disorder you most inherit mutations of both copies of the gene. If both parents both have a copy of the mutated gene, their children have a 25 percent of being born with PKU.


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How is PKU diagnosed?

In every state in the U.S. babies are tested for the disease by a blood sample when they are born. PKU must be treated early, so babies are tested as soon as possible.


How do you treat PKU?

Nearly all proteins contain phenylalanine, so people who have the disorder must have a protein-free diet.