Glycogen Storage Disease

Glycogen storage disease (GSD) is the name for a group of disorders that interfere with the body’s ability to make glycogen or convert glycogen into glucose. Depending on the type of GSD a child has, glycogen may build up in the liver, in the muscles, or both. GSD can also affect blood cells, the heart, kidneys, and other organs.

Glycogen is the body’s primary source of energy. Normally, glycogen is stored in the liver until the body needs energy. Then, enzymes convert glycogen into glucose so that it can travel through the bloodstream to cells that need fuel. Every cell in the body contains enzymes, but children with GSD lack one of the enzymes responsible for making glycogen or converting glycogen to glucose.

GSD is a rare condition. According to the National Organization of Rare Diseases, GSD affects fewer than 1 in 40,000 people in the United States.

What are the types of GSD?

There are many different types of GSD, based on which enzyme is missing. Some types affect only the liver, others only the muscles, while some affect both the liver and the muscles. Each type has slightly different symptoms. Treatments vary for the various types of GSD.

The most common types of GSD include:

Glycogen storage disease type I (GSD I), also known as von Gierke disease, accounts for about 25 percent of all children with GSD. Symptoms typically appear when an infant is 3 to 4 months of age and may include hypoglycemia (low blood sugar), which can cause fatigue, constant hunger, and crankiness. The liver and sometimes the kidneys swell due to built-up glycogen.

Glycogen storage disease type III (GSD III), also known as Cori disease or Forbes disease, causes glycogen to build up in the liver and muscles. Symptoms typically appear within the first year of life. Children with this type of GSD may have a swollen belly, delayed growth, and weak muscles.

Glycogen storage disease type IV (GSD IV), also known as Andersen disease, is one of the most serious types of GSD. Symptoms typically appear in a child’s first month of life and include failure to gain weight or grow at an expected rate. This type of GSD often leads to cirrhosis of the liver and can affect the heart and other organs as well. The child’s outcomes depend on the form of GSD IV they inherit.

What are the risks of GSD?

Each type of GSD carries specific risks.

Infants with type I (GSD I) may have low blood sugar. This type of GSD can also lead to lactic acidosis, a buildup of lactic acid, which can cause painful muscle cramps. As they mature into adolescence, children with GSD I may have delayed puberty and weak bones (osteoporosis). Other risks include:

• gout, a type of arthritis
• adenomas, tumors of the liver that are usually benign (non-cancerous)
• inflammatory bowel disease (type 1b)
• dental problems
• recurring infections (type 1b)
• pulmonary hypertension

Infants with type III (GSD III) may have low blood sugar and excess fat in their blood. As they get older, their livers may become enlarged. Some children’s livers go back to a normal size when they hit adolescence, but others develop cirrhosis and liver failure. Children with this type of GSD are also at risk for:

• slow growth and short stature
• muscle weakness

Infants with Type IV (GSD IV) may not have low blood sugar, but they can develop early complications. Children who survive with GSD IV are at risk for the following complications:

• slow weight gain
• muscle weakness, including a weak heart muscle
• cirrhosis
• portal hypertension