Glycogen storage disease type III (Cori-Forbes disease)

What happens in this disease?

The body stores sugar as glycogen in the liver and muscles. During fasting, this store is broken down to provide energy. In this disease, an enzyme that does this breakdown is missing. Glycogen cannot be fully broken down and builds up in the tissues. The liver and muscles are affected most.

Which symptoms can occur?

Symptoms usually begin in the first year of life. The course can be different in each person.

• A large liver and a swollen belly (very common)
• Low blood sugar during fasting (in about half)
• Poor weight gain and slow growth
• High levels of fats in the blood
• Muscle weakness in later years (in type 3a)
• Thickening of the heart muscle (sometimes)

How is it diagnosed?

Blood sugar, ketones, liver enzymes, fats and a muscle enzyme are measured in the blood. The diagnosis is confirmed with a genetic test that shows the change in the AGL gene. A liver ultrasound and heart tests are also done.

Treatment and care

The main treatment is diet. Not going hungry for long and having frequent, protein-rich meals are important. Slowly digested foods such as uncooked cornstarch may be used at night. Blood sugar and ketones are measured at home. The liver, heart and muscles are checked regularly. A transplant may be considered if the liver is badly damaged. The doctor who follows the disease decides which treatment is suitable.

For the family: inheritance and genetic counselling

The disease is passed on through recessive inheritance. The mother and father are usually healthy carriers. For a couple who are both carriers, the chance of having an affected child is 1 in 4 in each pregnancy. In marriages between relatives, the chance of carrying the same gene is higher. Genetic counselling is recommended for the family.