What is Pompe disease (acid maltase deficiency)?

Pompe disease, also known as acid maltase deficiency or glycogen storage disease type II, is part of a family of diseases known as lysosomal storage disorders. In people with Pompe disease, an enzyme called acid alpha-glucosidase (GAA) is not working properly. GAA's job is to make glycogen available to the body for fuel, in the form of glucose. But when GAA doesn't work properly, glycogen can build up in the body. A build up of glycogen in the body can cause problems. The extra glycogen stored in the cells damages muscles the most. 

Pompe disease is rare. It occurs in about 1 out of every 40,000 live births. It was named after the Dutch doctor who discovered it, J.C. Pompe. Pompe disease is a genetic condition. This means a problem with the genes causes the disease.

Pompe disease is a rare (estimated at one in every 40,000 births), inherited, and often fatal disorder, which disables the heart and muscles. It is caused by mutations in a gene that makes an enzyme called alpha-glucosidase (GAA). Normally, the body uses GAA to break down glycogen, a stored form of sugar used for energy. In Pompe disease, mutations in the GAA gene reduce or completely eliminate this essential enzyme. Excessive amounts of glycogen accumulate in the body, but the cells of the heart and skeletal muscles are the most seriously affected. Researchers have identified up to 70 different mutations in the GAA gene, which cause the symptoms of Pompe disease. The disease can vary widely in terms of age of onset and severity, both of which are related to the degree of enzyme deficiency.

Early onset (or infantile) Pompe disease is the result of complete or near complete deficiency of GAA. Symptoms begin in the first months of life, with feeding problems, poor weight gain, muscle weakness, floppiness, and head lag. Respiratory difficulties are often complicated by lung infections. The heart is grossly enlarged. More than half of all infants with Pompe disease also have enlarged tongues. Most babies with Pompe disease die from cardiac or respiratory complications before their first birthday.

Late onset (or juvenile/adult) Pompe disease 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, progressing to respiratory weakness, and death from respiratory failure after a course lasting several years. The heart may be involved but not grossly enlarged. Screening the patient for common genetic mutations, or measuring the level of GAA enzyme activity in a blood sample—a test that has 100 percent accuracy, confirms diagnosis of Pompe disease. Once the disease is diagnosed, testing of all family members and consultation with a professional geneticist is recommended. Carriers are most reliably identified through genetic mutation analysis.

This answer is based on source information from the National Institute of Neurological Disorders and Stroke.

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