In Type IV GSD there is not an increased amount of glycogen in the tissues, as in other forms of GSD. Instead, the glycogen that does accumulate has very long outer branches, because there is a genetic deficiency of the branching enzyme. This structural abnormality of the glycogen is thought to trigger the body's immune system, causing the body to actually attack the glycogen and the tissues in which it is stored. The result is tremendous scarring (cirrhosis) of the liver as well as other organs, such as muscle. The typical symptomatology of this disease is the result of the scarring process.
A baby with the typical Type IV GSD appears to be normal at birth. The first indication of a problem is a failure to thrive. The rate of growth and mental progress of the baby stops at a certain point and does not continue normally. The liver and spleen enlarge, there is little weight gain, and muscles develop poor tone. The course of the disease is one of progressive cirrhosis and associated problems. Death typically occurs by five years of age.
There have been a few older patients seen with severe muscle problems, who are found to have abnormal glycogen of the type associated with this type of glycogen storage disease.
Treatment for Type IV glycogen storage disease has been aimed at the failing liver, which has been symptomatic. Several patients have had liver transplants; however after transplantation, muscle and heart disease may still be a problem.