Glycogen storage disease type II
Glycogen storage disease type II (also called Pompe disease or acid maltase deficiency) is a neuromuscular, autosomal recessive metabolic lysosomal storage disease caused by a deficiency in the enzyme acid alpha-glucosidase, encoded by the GAA gene. The build-up of glycogen causes progressive muscle weakness (myopathy) throughout the body and affects various tissues, particularly the heart, skeletal muscles, liver, and nervous system. Wikipedia Pompe disease can be treated with an enzyme. Genzyme 
Pompe disease (pronounced "pom-PAY" in the United States, "pomp-uh" in Europe) occurs in about 1 in 40,000–300,000 births. It has an autosomal recessive inheritance pattern, so a child is not affected unless he or she inherits a defective copy of the gene from each parent; two carriers have a 1 in 4 chance of passing on the disorder to each of their children. Carriers of one defective allele usually have lower enzyme levels but typically do not show clinical signs of the disorder. Affected children vary considerably in their age of onset and progression of symptoms. Wikipedia Genzyme fact sheet Genetics Home Reference
The Pompe Center at the Erasmus University in Rotterdam, the Netherlands, maintains an up-to-date catalog of GAA mutations, including a table indicating the predicted severity of each variant. Not all SNPs in the GAA gene are associated with disease.
SNPs known to cause Pompe disease include the following:
- rs386834236 is thought to account for 36% - 90% of late-onset Pompe disease cases
- rs28940868 is often associated with Pompe disease in Taiwanese infants
Note: The 2010 movie Extraordinary Measures dramatizes the search for a cure for Pompe disease by a parent with two affected children. Wikipedia
An extended discussion in the New York Times "Well" blog for March 23 and 24, 2011 covers the symptoms and diagnosis of Pompe disease in a 10-year-old girl.