Description, Causes and Risk Factors:
Debrancher deficiency is caused by a deficiency of glycogen debrancher enzyme (GDE) activity. Glycogen debranching enzyme along with another enzyme, phosphorylase, helps break down the branches of glycogen to release free glucose. Deficiency of GDE results in glycogen with short outer chains in liver, muscle, and heart tissues. The abnormal glycogen is not soluble and causes damage to tissues where it collects (liver and/or muscle). This can be compared having a piece of sand in your shoe that, although small, irritates the foot. This partial breakdown of glycogen into glucose also causes hypoglycemia (low blood sugar) because glucose sugar can not be released. The body is unable to properly metabolize glycogen (a complex form of sugar). Because of improper processing, glycogen is stored in the organs of the body.
Debrancher deficiency is a genetic disorder and it is inherited as an autosomal-recessive disease. This means it is caused by a change in a part of an individual's genetic information. Genetic information is stored on genes. Genes serve as the instruction manual for our bodies. They tell the body how to grow and function. They also determine physical features, such as hair color and eye color. A person has around a 30,000 genes in every cell of their body. Two sets of every gene are inherited, one set from the Mother and one set from the Father.
If there is a change in the genetic information contained on one of these genes, the body is unable to read the instructions. Therefore, it may cause a difference in the way the body functions. This is similar to having a page missing out of an instruction manual for putting an appliance together. Without that page, one would be unable to properly assemble the appliance and it would not be able to work. The gene responsible for making debranching enzyme (GDE) is called the amylo-1, 6-glucosidase, 4-alpha-glucoanotransferase gene (AGL) gene. If one copy of the AGL gene is altered but the second copy is not, then the body can follow the instructions on the second copy in order to produce enough debranching enzyme. This is like having a second instruction manual to refer to. When both copies of an individual's AGL gene are altered, the body is unable to read any instructions on how to make the proper amount of debranching enzyme. As a result, the individual has debrancher deficiency.
People with debrancher deficiency have lived well into late adulthood. Muscle disorders seem to be an increasing problem with age in those persons with Type IIIa. Muscle weakness, though minimal during childhood, may become more evident in adults with onset in the third or fourth decade. These patients have slowly progressive weakness and distal muscle deterioration, and some patients eventually may require the use of a wheelchair for mobility. The heart may be mildly enlarged, but its function is typically normal. In rare instances, the heart muscle can thicken and result in heart failure and heart rhythm disturbances.
This disease principally affects the liver. It causes swelling of the liver, slowing of growth, low blood sugar levels and, sometimes, seizures.
In children, these symptoms often improve around puberty. Muscle weakness may develop later in life, and is most pronounced in the muscles of the forearms, hands, lower legs and feet. Weakness often is accompanied by loss of muscle bulk and exercise intolerance. The heart can be affected as well.
The diagnostic process usually begins with a careful medical history, a physical exam and a neurological exam to test reflexes, strength and the distribution of weakness. Several specialized tests are used to confirm a suspected diagnosis of metabolic disease:
An exercise test is used to monitor a person's response to intense or moderate exercise. Blood samples are taken during exercise for testing.
Electromyography (EMG) uses small needle electrodes to measure the electrical currents in a muscle as it contracts. While an EMG can't definitively diagnose metabolic disease, it can be used to rule out a number of other types of neuromuscular disease that cause similar patterns of weakness.
A muscle biopsy requires the removal of a small piece of muscle tissue for microscopic analysis. The procedure is done either surgically, with an incision to expose the target muscle or with a needle. A skin biopsy also is sometimes performed.
Other tests that may be needed include an electrocardiogram to test heart function, and brain imaging studies such as CT or MRI scans.
Blood tests can be used to detect the presence of certain chemicals in the blood that may indicate some metabolic diseases.
Currently, there is no effective treatment for this disease. Hypoglycemia (low blood sugar) can be controlled by frequent meals high in carbohydrates. Researchers have proven the storage of glycogen leads to liver cirrhosis progressing to liver failure. Patients with myopathy (weak muscles) have been tried on a diet high in protein, with some improvement; however, no long-term data is currently available.
Debrancher deficiency is considered a muscular dystrophy because of the weakness of the muscle. As a result, people with debrancher deficiency may qualify for services offered by the Muscular Dystrophy Association (MDA).
NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.
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