Phenylketonuria (PKU)
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Phenylketonuria (fen-ul-key-toe-NU-ree-uh), also called PKU, is a rare inherited disorder that causes an amino acid called phenylalanine to build up in the body. PKU is caused by a defect in the gene that helps create the enzyme needed to break down phenylalanine.
Without the enzyme necessary to process phenylalanine, a dangerous buildup can develop when a person with PKU eats foods that contain protein or eats aspartame, an artificial sweetener. This can eventually lead to serious health problems.
For the rest of their lives, people with PKU — babies, children and adults — need to follow a diet that limits phenylalanine, which is found mostly in foods that contain protein.
Babies in the United States and many other countries are screened for PKU soon after birth. Recognizing PKU right away can help prevent major health problems.
Newborns with PKU initially don’t have any symptoms. However, without treatment, babies usually develop signs of PKU within a few months.
PKU signs and symptoms can be mild or severe and may include:
The severity of PKU depends on the type.
But most children with the disorder still require a special PKU diet to prevent intellectual disability and other complications.
Women who have PKU and become pregnant are at risk of another form of the condition called maternal PKU. If women don’t follow the special PKU diet before and during pregnancy, blood phenylalanine levels can become high and harm the developing fetus or cause a miscarriage.
Even women with less severe forms of PKU may place their unborn children at risk by not following the PKU diet.
Babies born to mothers with high phenylalanine levels don’t often inherit PKU. But they can have serious consequences if the level of phenylalanine is high in the mother’s blood during pregnancy. Complications at birth may include:
Seek medical advice in these situations:
To have an autosomal recessive disorder, you inherit two mutated genes, one from each parent. These disorders are usually passed on by two carriers. Their health is rarely affected, but they have one mutated gene (recessive gene) and one normal gene (dominant gene) for the condition. With each pregnancy, two carriers have a 25 percent chance of having an unaffected child with two normal genes (left), a 50 percent chance of having an unaffected child who is also a carrier (middle), and a 25 percent chance of having an affected child with two recessive genes (right).
A defective gene (genetic mutation) causes PKU, which can be mild, moderate or severe. In a person with PKU, this defective gene causes a lack of or deficiency of the enzyme that’s needed to process phenylalanine, an amino acid.
A dangerous buildup of phenylalanine can develop when a person with PKU eats protein-rich foods, such as milk, cheese, nuts or meat, and even grains such as bread and pasta, or eats aspartame, an artificial sweetener. This buildup of phenylalanine results in damage to nerve cells in the brain.
For a child to inherit PKU, both the mother and father must have and pass on the defective gene. This pattern of inheritance is called autosomal recessive.
It’s possible for a parent to be a carrier — to have the defective gene that causes PKU, but not have the disease. If only one parent has the defective gene, there’s no risk of passing PKU to a child, but it’s possible for the child to be a carrier.
Most often, PKU is passed to children by two parents who are carriers of the disorder, but don’t know it.
Risk factors for inheriting PKU include:
Untreated PKU can lead to complications in infants, children and adults with the disorder. When mothers with PKU have high blood phenylalanine levels during pregnancy, fetal birth defects or miscarriage can occur.
Untreated PKU can lead to:
If you have PKU and are considering getting pregnant:
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Phenylketonuria (PKU)
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