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Glycogen storage diseases are caused by the lack of an enzyme needed to change glucose into glycogen and break down glycogen into glucose.
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Typical symptoms include weakness, sweating, confusion, kidney stones, a large liver, low blood sugar, and stunted growth.
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The diagnosis is made by doing blood tests, by examining a piece of tissue under a microscope (biopsy), and by doing magnetic resonance imaging.
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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 a copy of the abnormal gene. Because usually two copies of the abnormal 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 one of the enzymes that is essential to the process of forming glucose into glycogen or 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
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 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 at age 11 to 20 years or later.
Diagnosis
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. Other tests, such as liver, skin, muscle, and blood tests, are done to determine the specific type of glycogen storage disease. Genetic testing, which is used 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.
Some Types of Glycogen Storage Diseases
Treatment
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.
