Phenylketonuria (PKU) By: Greg Ancmon and Brennan Ramos Period 2

Overview Phenlyketonuria is a genetic disorder that is characterized by an inability of the body to utilize the amino acid, phenylalanine. The enzyme that breaks down phenylalanine, phenylalanine hydroxylase, is completely or nearly completely deficient. This enzyme normally converts phenylalanine into another amino acid, tyrosine. Without this enzyme, phenylalanine and its’ breakdown chemicals accumulate in the blood and body tissues. A normal phenylalanine level is 1 mg/dl ( milligrams/deciliter). In Phenylketonuria, levels may range from 6 to 80 mg/dl, but are usually greater than 30 mg/dl. Phenylalanine is an “essential amino acid” which is an amino acid that cannot be synthesized by the organism, and therefore must be supplied in the diet. It is structurally related to dopamine, epinepherine (adrenaline), and tyrosine.

Causes/Statistics Phenylketonuria is inherited in an autosomal recessive pattern, meaning two copies of the gene must be altered for a person to be affected by the disorder. (One altered gene from each parent), Generally, the parents of a child with an autosomal recessive disorder are not affected but are carriers of one copy of the altered gene. Classic PKU affect about one in every 10,000 to 20,000 Caucasian and oriental births. The incidence is far less in African Americans and is equally frequent in both male and females. PKU is most common in Turkey, where 1 in every 2,600 new borns are affected with the disorder.

Symptoms The signs and symptoms of Phenylketonuria vary from mild to severe. Most severe form of disorder is classic PKU. Infants appear normal until a few months old and without treatment these children can develop retardation and behavioral problems. Seizures, delayed development, movement disorders are also common. Children with PKU tend to have lighter skin and hair than unaffected family members because phenylalanine is important for skin pigmentation. (Eczema is also common). Affected women who have uncontrolled phenylalanine levels also have an increased risk of pregnancy loss. Excess phenylalanine damages nerve cells resulting in brain damage.

Prevention/Treatment Every state in the US now screens the blood phenylalanine levels of all newborns at the age of 3 days old. Newborn screening allows for early identification and early implementation of treatment. The goal of PKU treatment is to maintain the blood level of phenylalanine between 2mg/dl and 10 mg/dl. Although phenylalanine is needed for normal growth, a diet with some phenylalanine but in much lower amounts is required to control the levels. Foods high in protein, such as, meats, fish, eggs, cheese, and milk are all avoided. Periodic phenylalanine blood level measurements and a controlled diet make it possible to maintain a desirable blood level. Maintaining phenylalanine blood levels in the recommended range maximizes a persons ability with PKU to reach their potential for normal development and lifespan. There are no limitations for treated individuals.

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