What Is PKU?

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  • Written By: wiseGEEK Writer
  • Edited By: O. Wallace
  • Last Modified Date: 24 September 2019
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PKU or phenylketonuria is a condition that affects about 1 in 15,000 people. Those with this disorder lack the enzyme phenylalanine hydroxylase, which allows the body to turn ingested phenylalanine into the amino acid tyrosine. Tyrosine helps the body synthesize proteins, and where it is not present, the results can be quite devastating.

Newborns are routinely checked for PKU, because if they have the condition, which is inherited recessively, they must be on a special diet which is very low in phenylalanine. Phenylalanine unfortunately occurs in most proteins, like eggs, nuts, meat, and breast or dairy milk. Phenylalanine is also present in most infant formulas. If the child with the condition eats these foods, he or she will develop irreversible mental retardation, hence the mandatory testing.

The testing is fairly simple, though a bit hard to watch for new moms. The newborn’s heel is pricked, then a small amount of blood is squeezed out and sent to a lab for analysis. The lab results usually come back within a few days, since following dietary restrictions are vital for the newborn, and the child or adult with this disorder.


One will notice that many products clearly state whether or not they contain phenylalanines. You can see such labels on sodas, as well as on packaged nuts and cheese in most cases. As well as avoiding protein rich foods, most starch-laden foods like potatoes and pasta have to be avoided as well, so the diet is limited. To give the body the necessary protein it needs, protein formulas have been specifically developed for those with PKU so they can grow and develop normally.

When women with this condition become pregnant, the presence of PKU in the fetal environment is linked to birth defects of varied types. It is particularly important that pregnant women with this disorder seek the advice of a high-risk obstetrician. Most important is a strict adherence to a PKU diet during the pregnancy to prevent birth defects in the fetus.

Since the diet of the person affected by the disorder is restrictive, there are many companies that now manufacture PKU foods that are very low in or completely absent of phenylalanines. These products, like egg substitutes, ice cream substitutes, and various soups or spaghetti sauces, as well as low protein breads and pastas, can help the person with this condition have a relatively normal diet. However, the cost of such food can be expensive, particularly for the more fancy substitutions.

With the proper diet, the person with this condition can expect to live a long and healthy life. His or her food choices may be limited, but generally PKU will cause no other symptoms or result in complications as the person ages.


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