WHAT IS GLYCOGEN STORAGE DISEASE?

Glucose is a major source of energy for the body. It is stored in the form of glycogen in both the liver and muscles and later released with the help of enzymes. Persons affected by GSD have an inherited defect in one of the enzymes responsible for forming or releasing glycogen as it is needed by the body during exercise and/or between meals.

There are about eleven known types of GSD which are classified by a number, by the name of the defective enzyme, or by the name of the doctor who first described the condition. For example, GSD I, a defect in the enzyme glucose-6-phosphatase, was originally known as von Gierke's Disease.

GSD can affect the liver, the muscles or both. Diagnosis of the type of GSD is made on the basis of an individual's symptoms, the results of a physical examination and of biochemical tests. Occasionally, a muscle or liver biopsy is required to confirm the a ctual enzyme defect.

All forms of GSD, except some forms of the liver phosphorylase kinase deficiency (GSD IX), occur when a child inherits the affected gene from both parents (autosomal recessive inheritance) each of whom is a carrier but not affected them selves. This means that for each pregnancy there is a 1 in 4 chance that the child will inherit both defective genes and thereby be affected.