Glycogen Storage Disease (GSD)

WHAT IS GSD?

In most types of GSD, one of the enzymes responsible for forming or releasing glycogen as it is needed by the body (during exercise and/or between meals) is either faulty or missing. Glycogen is the form in which glucose (a major source of energy for the body) is stored in both the liver and muscle s.

There are 11 known types of GSD which are classified by a number (e.g. Type III), by the name of the defective enzyme (e.g. debrancher enzyme deficiency), or by the name of the doctor who first described the condition (e.g. Con). Some forms of GSD cause little in the way of illness, while others are life-threatening.

N.B. Chris (see Genes and you: Unit I) has GSD IX, which is one of the least severe forms of GSD, and one of the rarest.

OTHER INFORMATION

Management of the symptoms is usually by special diet. Children with GSD I need frequent glucose intake during the day and many need continuous overnight feeding through a tube which is passed down the nose and into the stomach. As they get older, those with GSD I may have regular intake of corn-starch (or cornflour) mixed into drinks. This starch gives a slow release of glucose. For those with GSD III a high carbohydrate (bread, pasta, rice) diet gives glucose slowly over the day and lots of protein in the diet (milk, meat, lentils) helps with muscle problems. Symptoms in other types of GSD also have to be managed.

If you are interested in finding out more about GSD, you can write (enclosing an A5 stamped addressed envelope) to: Ann Phillips, Association for Glycogen Storage Disease (UK), 9 Lindop Road, Hale, Altrincham, Cheshire WA15 9DZ.

HOW IS GSD PASSED ON?

The pattern of inheritance for GSD (except in GSD Type IX) is autosomal recessive. A person who inherits one faulty gene for GSD will be a carrier. Carriers are usually unaffected but can pass the faulty gene onto any children they may have. If one or both parents is a carrier, there is a 50% (1 in 2) chance that each child of theirs will also be a carrier.

A child who inherits two copies of the faulty gene (one from each parent) will have GSD. If both parents are carriers, there is a 25% (1 in 4) chance of this happening.

N.B. Chris (see Genes and you: Unit 1) inherited GSD IX in a "slightly different way. He inherited a copy of the faulty gene on his mother's X chromosome (X-linked inheritance).

A PERSON WITH LESS SEVERE GSD MAY BE AFFECTED BY SOME, OR ALL, OF THE FOLLOWING:

Children with the more severe forms of GSD (e.g. Type II, Type IV) do not usually survive after the age of 2 years. Sadly they may die from heart or liver failure.

• An enlarged liver.
• Poor growth.
• Muscle weakness, which may be severe and cause painful cramps during exercise.
• Sweating and irritability.
• Low blood sugar.

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