What is PKU?

PKU stands for phenylketonuria, a recessive hereditary disease caused by the body’s failure to oxidize an amino acid (phenylalanine) to tyrosine, because of a defective enzyme.

  • Because it is recessive, parents may carry the gene without knowing it, since they might not actually have PKU. However, two individuals who carry the gene have a 1 in 4 chance of having a child with PKU.

  • Because it is hereditary, it may not be detected until it has caused problems for the child. If it is not treated before the age of three, brain damage may occur, causing severe mental retardation. Indiana requires hospitals to draw blood from all newborn babies and send it to the James Whitcomb Riley Hospital for Children in Indianapolis, where it is tested for PKU and about 30 other inborn errors of metabolism.

  • Because it deals with the body’s ability to use an amino acid, it affects the child’s ability to eat any natural protein source. All natural proteins contain all amino acids, so phenylalanine cannot be avoided. Most foods contain some natural protein, including not only meats, fish, dairy, and eggs, but also all fruits, vegetables, and grains.

  • Because the phenylalanine (phe) is not properly metabolized by the body, it causes progressive, cumulative damage to brain cells. Untreated cases may result in severe mental retardation, extremely low IQ, impaired language ability, physical disability, and nutritional deficiencies.

How is PKU treated?

After a child is diagnosed with PKU, he or she is immediately placed on a low-protein diet. Instead of regular formula, a baby must drink a special formula which has phenylalanine removed. The person with PKU will continue to drink a similar formula (about 24 to 32 ounces per day) for the rest of his or her life. The formula is nearly nutritionally complete except for calories and the small amount of phenylalanine needed for growth.

The child or adult with PKU must measure all foods in order to restrict the amount of phenylalanine eaten. No meat, fish, eggs, nuts, or soybeans are allowed, and only limited amounts of dairy and vegetables. Most of an adult’s calories come from the formula and from low-protein vegetables, fruits, and special low-protein processed foods made from finely milled grains.

After the age of three, there is no danger of permanent brain damage, but if the diet is not followed, the child or adult may suffer significant developmental delays, learning disabilities, attention problems, short-term memory loss, stunted growth, and nutritional deficiencies. The formula and the low-protein foods are very expensive, but the state of Indiana only requires insurance coverage for the formula.

What can research accomplish?

Current research is focused on replacing the missing enzyme for metabolizing phenylalanine, genetically altering PKU patients so their liver will make the enzyme, or genetically altering natural protein sources so that they will not have as much phenylalanine.