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. Glycogen is stored in the liver. When the body needs more energy, certain proteins called enzymes break down glycogen into glucose. They send the glucose out 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 correctly. This can cause problems in the liver or muscles, or other parts of the body.

GSD is passed down from parents to children (hereditary). It is most often seen in babies or young children. But some forms of GSD may appear in adults.

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 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 disease. People with type III don't have enough of an enzyme (the debranching enzyme) that helps break down glycogen. 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 Andersen disease. People with type IV form abnormal glycogen. Experts think the abnormal glycogen triggers the body's infection-fighting system (immune system). This creates scarring (cirrhosis) of the liver and other organs, such as muscle and the heart. People with type IV disease may develop liver failure at a young age or develop heart failure.

Glycogen storage disease is passed down from parents to children (hereditary).

It happens because both parents have an abnormal gene (gene mutation) that affects a specific way that glycogen is stored or used. Most GSDs occur because both parents pass on the same abnormal gene to their children.

In most cases, parents don't show any symptoms of the disease.

Glycogen storage disease is passed down from parents to children (inherited). Someone is more at risk for GSD if they have a family member with the disease.

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 which enzyme they are 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)

The symptoms of GSD may look like other health problems. Always see your child's doctor to be sure.

Some types of GSD can appear in adults. See your doctor if you think you may have GSD.

Your child's doctor will ask about your child's symptoms and past health. The doctor will do a physical exam to check for symptoms, such as an enlarged liver or weak muscles.

Your child's doctor may do a few blood tests. They may also take a small tissue sample (biopsy) of your child's liver or muscle. The sample will be taken to a lab. It will be tested to see how much of a certain enzyme is in that part of the body. Genetic testing may also be sent to confirm the subtype diagnosis.

If you are pregnant and concerned about GSD, your doctor may do some tests before your baby is born (prenatal tests) to check for GSD.

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. Frequent feedings may be needed to prevent low blood sugar. In some cases, your child may need overnight feeding via a nasogastric tube. 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. They may need to have a medical treatment to replace the enzyme that is missing (enzyme replacement therapy).

Glycogen buildup can hurt the liver, the heart, the neurologic system, and muscles. This can create other problems if your child has certain types of GSD, such as:

• Type I. This can cause arthritis, dental problems, inflammatory bowel disease, recurring infections, and harmless (benign) tumors in the liver.
• Type III. This can cause harmless (benign) tumors in the liver. Slow growth and muscle weakness are also common with this type of glycogen storage disease.
• Type IV. Over time, this can cause scarring (cirrhosis) of the liver. This disease leads to liver failure.

Severe illness may lead to liver cirrhosis and cardiomyopathy. This is a problem with the heart muscle. These may need supportive treatment as the symptoms get worse. Your child may need a liver transplant if they have severe liver disease.

There is no way to prevent glycogen storage disease. But early treatment can help control symptoms once a child has GSD.

If you or your partner have GSD, or a family history of this disease, see a genetic counselor before you get pregnant. They can find out your chances of having a child with GSD.

A child with GSD may have special needs and will need continued follow up with multiple doctors. Be sure that your child gets regular medical care. It is important that your child's doctor checks their condition. Regular medical visits will also help you keep up with new treatment choices. Teach your child and any siblings about GSD in an age-appropriate manner. An educated, supportive, family approach will help your child cope with the illness and also help family members manage the stress of a chronic illness.

Online or in-person support groups may also be helpful for you and your family.

Many forms of glycogen storage disease appear in babies and young children.

Call your doctor if your baby's behavior changes after you stop night feedings.

Talk with your doctor if your child:

• Is not growing fast enough
• Has constant (chronic) hunger
• Has a swollen belly

Teens and adults should watch for the following symptoms when they exercise:

• Muscle weakness
• Pain
• Cramps

• Glycogen storage disease (GSD) is a rare condition that changes the way the body uses and stores glycogen, a form of sugar.
• It is passed down from parents to children (inherited). For most GSDs, each parent must pass on one abnormal copy of the same gene.
• Most parents do not show any signs of GSD.
• There are at least 15 known types of GSD. Each GSD has its own symptoms and needs different treatment.
• Symptoms often first appear in babies or young children. In some cases, GSD can appear in adults.

Tips to help you get the most from a visit to your child's doctor:

• Know the reason for the visit and what you want to happen.
• Before your visit, write down questions you want answered.
• At the visit, write down the name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new instructions your doctor gives you for your child.
• Know why a new medicine or treatment is prescribed and how it will help your child. Also know what the side effects are.
• Ask if your child's condition can be treated in other ways.
• Know why a test or procedure is recommended and what the results could mean.
• Know what to expect if your child does not take the medicine or have the test or procedure.
• If your child has a follow-up appointment, write down the date, time, and purpose for that visit.
• Know how you can contact your child's doctor after office hours and on weekends and holidays. This is important if your child becomes ill and you have questions or need advice.