Glycogen storage diseases are carbohydrate metabolism disorders that occur when there is a defect in the enzymes that are involved in the metabolism of glycogen, often resulting in growth abnormalities, weakness, a large liver, low blood sugar, and confusion. Glycogen storage diseases occur when parents pass on to their children the defective genes that cause these diseases.
Glycogen storage diseases are caused by the lack of an enzyme needed to change glucose into glycogen or break down glycogen into glucose.
Typical symptoms include weakness, sweating, confusion, kidney stones, a large liver, low blood sugar, and stunted growth.
The diagnosis is made by doing blood tests, by examining a piece of tissue under a microscope (biopsy), and by doing magnetic resonance imaging.
Treatment depends on the type of glycogen storage disease and usually involves regulating the intake of carbohydrates.
There are different types of inherited disorders. In many hereditary metabolic disorders, both parents of the affected child carry 1 copy of the abnormal gene. Because usually 2 copies of the abnormal (recessive) gene are necessary for the disorder to occur, usually neither parent has the disorder. (See also Overview of Hereditary Metabolic Disorders.)
Glycogen (a carbohydrate) is made of many glucose molecules linked together. The sugar glucose is the body’s main source of energy for the muscles (including the heart) and brain. Any glucose that is not used immediately for energy is held in reserve in the liver, muscles, and kidneys in the form of glycogen and is released when needed by the body.
Children who have a glycogen storage disease are
Missing 1 of the enzymes that is essential to forming glucose into glycogen
Missing 1 of the enzymes that is essential to breaking down (metabolizing) glycogen into glucose
About 1 in 25,000 infants has some form of glycogen storage disease.
There are many different glycogen storage diseases (also called glycogenoses). Each is identified by a Roman numeral.
Symptoms of Glycogen Storage Diseases
Some of these diseases cause few symptoms. Others are fatal. The specific symptoms, age at which symptoms start, and their severity vary considerably between these diseases.
For types II, V, and VII, the main symptom is usually weakness (myopathy).
For types I, III, and VI, symptoms are low levels of sugar in the blood (hypoglycemia) and protrusion of the abdomen (because excess or abnormal glycogen may enlarge the liver). Low levels of sugar in the blood cause sweating, confusion, and sometimes seizures and coma.
Other consequences for children who have a GSD may include stunted growth, frequent infections, and sores in the mouth and intestines.
Glycogen storage diseases tend to cause uric acid (a waste product) to accumulate in the joints, which can cause gout, and in the kidneys, which can cause kidney stones. In type I glycogen storage disease, kidney failure is common.
Diagnosis of Glycogen Storage Diseases
Blood tests, biopsy, and magnetic resonance imaging
Glycogen storage disease is diagnosed by examining a piece of muscle or liver tissue under a microscope (biopsy) and by doing magnetic resonance imaging (MRI) to detect glycogen in the tissues. Doctors confirm the diagnosis by analyzing the DNA. Glycogen storage disease type II (Pompe disease) is now part of the screening test for newborns in many states in the United States.
Other tests, such as liver, skin, muscle, and blood tests, are done to determine the specific type of glycogen storage disease.
Genetic testing to determine whether a couple is at increased risk of having a baby with a hereditary genetic disorder is also available. (See also diagnosis of hereditary disorders of metabolism.)
Treatment of Glycogen Storage Diseases
Carbohydrate-rich diet
Prevention of low blood sugar through frequent or nearly continuous feedings
Treatments for specific complications
Treatment depends on the type of glycogen storage disease.
For most types, eating many small carbohydrate-rich meals every day helps prevent blood sugar levels from dropping.
For people who have glycogen storage diseases that cause low blood sugar levels, levels are maintained by giving uncooked cornstarch every 4 to 6 hours around the clock, including overnight.
For others, it is sometimes necessary to give carbohydrate solutions through a stomach tube all night to prevent low blood sugar levels from occurring at night.
People who have a glycogen storage disease that affects the muscles should avoid excessive exercise.
Specific complications, such as heart or liver problems, are treated as needed.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
National Organization for Rare Disorders (NORD): This resource provides information to parents and families about rare diseases, including a list of rare diseases, support groups, and clinical trial resources.
Genetic and Rare Diseases Information Center (GARD): This resource provides and easy to understand information about rare or genetic diseases.
