Fighting Pompe Disease -- Research Summary

BACKGROUND: Pompe disease is an inherited, neuromuscular disorder that causes progressive muscle weakness. It is a rare disease, affecting about 1 in every 40,000 births. Pompe disease is caused by a defective gene that results in a deficiency of an enzyme known as acid alpha-glucosidase (GAA). The lack of this enzyme results in excessive build-up of glycogen -- a form of sugar -- in a specialized compartment of muscle cells throughout the body. Researchers have identified up to 300 different mutations in the GAA gene that cause the symptoms of Pompe disease. The severity of the disease and the age of onset are related to the degree of enzyme deficiency. There are two types of Pompe disease. These include:

• Early onset (the infantile form): This is the result of complete or near-complete deficiency of GAA. Symptoms such as feeding problems, poor weight gain, muscle weakness, floppiness, and head lag usually start during the first months of life. Respiratory difficulties are often complicated by lung infections. The heart is also very enlarged. Many infants with Pompe disease also have enlarged tongues. Most babies die from cardiac or respiratory complications before their first birthday.

• Late onset (juvenile/adult form): This is the result of a partial deficiency of GAA. The onset can be as early as the first decade of childhood or as late as the sixth decade of adulthood. The primary symptom is muscle weakness that progresses to respiratory weakness. The heart is usually not involved. (SOURCE: NIH)

MYOZYME: Myozyme is a lysosomal glycogen-specific enzyme that essentially replaces the enzyme Pompe disease patients are lacking. The treatment has to be given throughout the course of a patient’s life. “This is the first lifesaving treatment that is FDA approved for Pompe disease,” Priya S. Kishnani, M.D., C.L. and Sue Chen Professor of Pediatrics/Division Chief, Medical Genetics, Duke University Medical Center, told Ivanhoe. “Prior to 2006, there was no treatment for Pompe disease other than symptomatic care.”

HELPING MORE KIDS SURVIVE LONGER: Some children develop an immune reaction that blocks the effects of Myozyme treatment. However, researchers at Duke, along with collaborators at other centers, have found that a very low-dose combination of medicines typically used to treat cancer is successful in eliminating or preventing the immune response in these patients. The drugs -- rituximab, methotrexate, and gammaglobulins -- are a mix of chemotherapeutic agents. The chemo drugs allow the patients to tolerate and respond to the Myozyme treatment, which is the only therapy for these kids. “It was really rewarding because the babies did not make antibodies and continued to do well clinically,” Dr. Kishnani said. “The oldest child is now over 5 years of age, remains antibody-negative and has come off all chemotherapy.” Dr. Kishnani says prior to the chemo discovery, children who developed antibodies and could not benefit from Myozyme would have died. (SOURCE: Duke University press release) MORE
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