Home-testing kits have made it easier for diabetics and hypertension patients to track their conditions, but such self-monitoring hasn’t been possible for people with phenylketonuria (PKU). Georgia Tech researchers and an Atlanta start-up company hope to change that by introducing the first home-testing device for PKU patients.
PKU is a genetic metabolic disorder in which the body lacks a liver enzyme (phenylalanine hydroxlase) needed to process phenylalanine, an essential amino acid, into another amino acid (tyrosine) used by the body. Left unconverted, excessive amounts of phenylalanine in the bloodstream are toxic to brain tissue and the central nervous system; if untreated in newborns, PKU can cause brain damage and mental retardation.
There is no drug that can cure PKU. It can only be treated through diet. Because phenlylalanine is a component of proteins, patients must follow a strict low-protein diet, avoiding meat, fish, eggs, poultry, dairy and soy products as well as products containing the artificial sweetener aspartame. “When phenylalanine levels become too high, PKU patients can suffer movement disorders, such as tremors, seizures and hyperactivity,” explains Jeff Sitterle, chief scientist at the Georgia Tech Research Institute (GTRI) and project director for the PKU testing device.
Blood-testing requirements vary depending on the severity of a patient’s condition, but frequent monitoring is especially important for children. The goal is to maintain phenylalanine levels in the blood between 2 and 10 milligrams per deciliter. Pregnant women must also be careful, for if phenylalanine levels get too high, it can affect development of the fetus.
In the United States, there are about 120 centers where PKU monitoring is conducted. That means frequent testing can be costly and inconvenient for patients who must travel long distances to reach a center.
Because PKU is considered an “orphan disease” – one that affects a small sector of the population – large pharmaceutical companies haven’t pursued a home test for the disease.
“Incidence of PKU varies around the world,” says Richard Shunnarah, president of Atlanta-based MetGen Inc., which is developing blood-monitoring devices for metabolic genetic disorders. In the United States, PKU occurs in about one in 10,000 births, but varies from a low of 1 in 100,000 births in Japan to a high of 1 in 2,600 births in Turkey, he adds.
A 20-year veteran of the clinical nutrition industry, Shunnarah launched MetGen in 2002 and approached Georgia Tech for assistance in developing a PKU home test. Sitterle, whose great-niece suffers from the disease, quickly recognized the significance of the project.
“PKU patients can keep records of what they eat, but there’s no way to know what their blood levels are without frequent testing,” Sitterle says. “A home test will help patients understand how their bodies react to food.”
What’s more, the testing device will store data, providing a history for doctors to review during patients’ routine checkups. “That gives doctors a true trend picture, rather than blood levels that might have resulted from patients making a sudden effort to stick to their diet prior to the checkup,” Sitterle adds.
An interdisciplinary project, GTRI engineers have built the electronics for the PKU home test while Sheldon May, a Regents professor in Georgia Tech’s School of Chemistry and Biochemistry, has developed a special reagent strip for the device, assisted by graduate student Veronica de Silva.
Similar to a blood-glucose home test, a PKU patient pricks his or her finger and then places a drop of blood on the reagent strip inserted in the testing device. Phenylalanine in the blood causes a reaction to take place on the test strip. Then electronics in the device calculate the rate at which the test strip absorbs a specific color of light. This rate indicates the level of phenylalanine in the blood.