Some GSDs affect the liver (I, IV, VI and IX), some the muscles (V and VII) and some affect both (type III).
Conditions affecting the liver cause liver enlargement with a tendency for low blood sugar. Untreated children with liver GSDs tend to be short; with enlarged abdomens and thin limbs. These problems improve dramatically with treatment. A few may develop problems of liver scarring and very occasionally liver tumours. In GSD I there can also be longer term problems with kidney disease. In GSD I there are 2 subtypes Ia and Ib. People with GSD Ib have an increased risk of infections because of a decrease in a particular type of white blood cell.
Disorders affecting muscle may cause muscle weakness or cramping. Excessive exercise may trigger bouts of muscle inflammation. The heart and respiratory (breathing) muscles may be affected, but not in all types.
All types of GSD are at risk of ostepaenia (decreased bone strength), which increases fracture risk in later life.
Type II GSD (see entry Pompe disease) is a disease of heart and muscle but is very different to the other GSDs.