By: Devun Pontrelli


PKU, short for phenylketonuria, is a rare inherited disorder that causes an amino acid called phenylalanine to build up in your 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 are high in protein. This can eventually lead to serious health problems.

How PKU is inheredited

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 have the defective gene, but not have the disease. This is called being a carrier. If only one parent has the PKU gene, there's no risk of passing PKU to a child, but it is 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.

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Diagnostic Tests

Newborn blood testing identifies almost all cases of phenylketonuria. All 50 states in the United States require newborns to be screened for PKU. Many other countries also routinely screen infants for PKU. A PKU test is done a day or two after the baby's birth. The test isn't done before the baby is 24 hours old or before the baby has ingested some protein in the diet to ensure accurate results.

Symptoms Of PKU if not Treated

PKU patients have a broad range of symptoms that include severe mental retardation. Other symptoms can include extreme patterns of delayed speech development, seizures, abnormal small head, body odor, light body pigmentation.

Treatment for patients with PKU disorder

There is no known treatment that can fully get rid of PKU. However in the early 1950s, researchers discovered phenylalanine-restricted diets could eliminate most PKU symptoms, but not mental retardation. PKU patients who receive early and consistent dietary therapy can develop fairly normal mental capacity to within about five IQ points of healthy people around their age. Dietary Therapy is the most common treatment for PKU patients.
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The Food and Drug Administration (FDA) has approved the drug sapropterin (Kuvan) for the treatment of PKU. It works by increasing your tolerance to phenylalanine. The drug is for use in combination with a PKU diet. But it doesn't work for everyone with PKU. In approving sapropterin, the FDA directed that studies continue because there are no long-term studies on the drug's efficacy and long-term safety.

Studies of PKU

The Disease, or genetic disorder, PKU, was not discovered until around 1934, by a Norwegian physician and biochemist named Asbjorn Folling (Right). While Folling was studying two mentally retarded siblings, he noticed that their urine turned a deep green when he added ferric chloride to it. After becoming very interested in why that occurred Folling started to test other mentally retarded youngsters, hoping to find whatever substance in their urine caused their urine to change color when he added ferric Chloride to it. Folling eventually found that the substance was phenylpyruvic acid. Folling then went on to see if it was in all the youngsters he tested and it was, which led him to believe that PKU, not being able to break down the amino acid phenylaline, had a connection to mental and physical Retardation.