Pompe disease is a rare (estimated at 1 in every 40,000 births) inherited and often fatal disorder that disables the heart and muscles. It is caused by mutations in a gene that makes an enzyme called alpha-glucosidase (GAA).
Glycogen storage disease type II (also called Pompe disease or acid maltase deficiency) is an autosomal recessive metabolic disorder which damages muscle and nerve cells throughout the body. It is caused by an accumulation of glycogen in the lysosome due to deficiency of the lysosomal acid alpha-glucosidase enzyme.
Acid Maltase Deficiency (AMD), Alpha-1,4 Glucosidase Deficiency, Cardiomegalia Glycogenica Diffusa, Generalized Glycogenosis (Cardiac), Glycogen Storage Disease type II, Glycogenosis type II, Lysosomal Glucosidase Deficiency.
Normally, the body uses GAA to break down glycogen, a stored form of sugar used for energy. But in Pompe disease, mutations in the GAA gene reduce or completely eliminate this essential enzyme. Excessive amounts of glycogen accumulate everywhere 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 that cause the symptoms of Pompe disease, which can vary widely in terms of age of onset and severity. The severity of the disease and the age of onset are related to the degree of enzyme deficiency.
Infantile form occurs within 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.
A diagnosis of Pompe disease can be confirmed by screening for the common genetic mutations or measuring the level of GAA enzyme activity in a blood sample - a test that has 100 percent accuracy.
There is no cure for Pompe disease.
Treatment, therefore, serves only to help minimize the symptoms.
The clinical course is typically not affected by drugs that are used to treat the respiratory or cardiac defects.
A high protein diet may be helpful and has led to significant improvements in respiratory function in some cases.
An enzyme replacement therapy has been developed that has shown, in clinical trials with Infantile Pompe Disease, to decrease heart size, maintain normal heart function, improve muscle function, tone, and strength, and reduce glycogen accumulation.
A drug called alglucosidase alfa (Myozyme), has received FDA approval for the treatment of Pompe disease.
Most babies with the Infantile form of Pompe disease die from cardiac or respiratory complications before their first birthday.
Without enzyme replacement therapy, the hearts of babies progressively thicken and enlarge.
As with all cases of autosomal recessive inheritance, children have a 1 in 4 chance of inheriting the disorder when both parents carry the defective gene, and although both parents carry one copy of the defective gene, they are usually not affected by the disorder.
The incidence of the disease is approximately 1 in 140,000 for infantile GSD II and 1 in 60,000 for adult GSD II.