Glycogen Storage Disease
What is glycogen storage disease (GSD)?
Glycogen storage disease (GSD) is a rare condition that changes the way the body uses and stores glycogen, a form of sugar or glucose.
Glycogen is a main source of energy for the body, and is stored in the liver. When the body needs more energy, certain proteins called enzymes break down glycogen into glucose, and send the glucose into the body.
When someone has GSD, they are missing one of the enzymes that breaks down glycogen. When an enzyme is missing, glycogen can build up in the liver, or glycogen may not form properly. This can cause problems in the liver, muscles or other parts of the body.
GSD is hereditary and is passed down from parents to children. It is most often seen in babies or young children, but some forms of GSD may appear in adults.
What are the different types of GSD?
Experts know of at least nine types of GSD. They are grouped by the enzyme that is missing in each one. Each GSD has its own symptoms and needs different treatment.
The most common types of GSD are types I, III, and IV:
Type I or von Gierke’s disease. This is the most common form of GSD. People with type I don’t have the enzyme needed to turn glycogen into glucose in the liver. Glycogen builds up in the liver. Symptoms often appear in babies around 3 to 4 months old. They may include low blood sugar (hypoglycemia) and a swollen belly because of an enlarged liver.
Type III or Cori’s disease. People with type III don’t have enough of an enzyme that helps break down glycogen, and the glycogen can’t fully break down. It collects in the liver and in muscle tissues. Symptoms include a swollen belly, delayed growth and weak muscles.
Type IV or Anderson’s disease. People with type IV form abnormal glycogen. Experts think the abnormal glycogen triggers the body’s immune system, creating scarring (cirrhosis) of the liver and other organs such as muscle and the heart.
What are the signs and symptoms of GSD?
With many types of GSD, symptoms first appear in babies or in very young children. Symptoms will vary based on the type of GSD a child has, and on which enzyme he or she is missing.
Because GSD most often affects the muscles and the liver, those areas show the most symptoms.
General symptoms of GSD may include:
- Not growing fast enough
- Not feeling comfortable in hot weather (heat intolerance)
- Bruising too easily
- Low blood sugar (hypoglycemia)
- An enlarged liver
- A swollen belly
- Weak muscles (low muscle tone)
- Muscle pain and cramping during exercise
Symptoms for babies may include:
- Too much acid in the blood (acidosis)
- High blood cholesterol levels (hyperlipidemia)
How is GSD diagnosed?
GDS may be suspected after a thorough physical examination if your physician notices the different symptoms and findings that are characteristic of GDS. Your child’s doctor will do a physical exam to check for symptoms such as an enlarged liver or weak muscles.
Your child’s provider may do a few blood tests. He or she may also take a small tissue sample (biopsy) of your child’s liver or muscle. The sample will be tested to see how much of a certain enzyme is in that part of the body.
How is GSD treated?
Treatment will vary depending on what type of GSD your child has.
For types I, III, and IV, your child’s doctor may suggest a special diet to help control symptoms. Your child may also have to take certain medicines.
For other types of GSD, your child may need to limit exercise to avoid muscle cramps. He or she may need to have a medical treatment to replace the enzyme that is missing (enzyme replacement therapy).
What are the complications of GSD?
Glycogen buildup can hurt the liver and muscles. This can create other problems if your child has certain types of GSD such as:
Type III. This can cause harmless (benign) tumors in the liver.
Type IV. Over time this can cause scarring (cirrhosis) of the liver.