Glycogen storage diseases are caused by the lack of an enzyme needed to change glucose into glycogen and 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 Inheritance of Single-Gene Disorders Genes are segments of deoxyribonucleic acid (DNA) that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are made of a very long strand... read more . 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 Overview of Hereditary Metabolic Disorders Hereditary metabolic disorders are inherited genetic conditions that cause metabolism problems. Heredity is the passing of genes from one generation to the next. Children inherit their parents'... read more .)
Glycogen (a carbohydrate Carbohydrates Carbohydrates, proteins, and fats supply 90% of the dry weight of the diet and 100% of its energy. All three provide energy (measured in calories), but the amount of energy in 1 gram (1/28 ounce)... read more ) 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 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 Hypoglycemia Hypoglycemia is abnormally low levels of sugar (glucose) in the blood. Hypoglycemia is most often caused by drugs taken to control diabetes. Much less common causes of hypoglycemia include other... read more ) 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 Gout Gout is a disorder in which deposits of uric acid crystals accumulate in the joints because of high blood levels of uric acid (hyperuricemia). The accumulations of crystals cause flare-ups ... read more , and in the kidneys, which can cause kidney stones Stones in the Urinary Tract Stones (calculi) are hard masses that form in the urinary tract and may cause pain, bleeding, or an infection or block of the flow of urine. Tiny stones may cause no symptoms, but larger stones... read more . In type I glycogen storage disease, kidney failure is common at age 11 to 20 years or later.
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 Magnetic Resonance Imaging (MRI) In magnetic resonance imaging (MRI), a strong magnetic field and very high frequency radio waves are used to produce highly detailed images. MRI does not use x-rays and is usually very safe... read more (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 Genetic Screening Genetic screening is used to determine whether a couple is at increased risk of having a baby with a hereditary genetic disorder. Hereditary genetic disorders are disorders of chromosomes or... read more , 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 Diagnosis Hereditary metabolic disorders are inherited genetic conditions that cause metabolism problems. Heredity is the passing of genes from one generation to the next. Children inherit their parents'... read more .
Treatment of Glycogen Storage Diseases
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.