Forbes disease is a form of glycogen storage disease. This means that Forbes disease is an autosomal recessive metabolic disease. It is an inborn error of metabolism. Forbes disease is evidenced by a deficiency in glycogen debranching enzymes.
Forbes disease is a genetically linked metabolic disease that has to do with the enzymes regulating glycogen metabolism. This is similar to the other glycogen storage diseases. These enzymes play a part in the synthesis or processing of glycogen breakdown inside of your ahaha muscles, liver and other cell types.
Each one of the steps in the process of glycogen breakdown is determined by a different enzyme. If any one of these enzymes is defective, the process is halted and its step in the process is not completed. The kind of glycogen storage disease that you have depends on which one of the enzymes is faulty and does not complete its step in the process.
Fortunately, Forbes disease is a rare disease that takes place in about 1 out of every 100,000 live births. Forbes disease is marked by a missing enzyme that causes abnormal amounts of glycogen to be placed in your heart, liver and skeletal muscles. This may stunt your growth and result in hypoglycemia, acidosis and an enlarged liver.
Forbes disease is called by other names. It is also referred to as glycogen storage disease type III, dextrinosis and Cori’s disease.
The 1947 Nobel laureates Carl Cori and Gerty Cori were the first to describe this disease. Gilbert Burnett Forbes was a clinician who additionally described features of this disease that bears his name.
The clinical course of Forbes disease is like that of glycogen storage disease type I. Forbes disease is generally, but not always, milder. Massive hepatomegaly (swelling and enlargement of your liver) usually takes place in young children. It may then diminish. Hepatomegaly may even disappear as you age. Levels of glycogen with short outer branches are raised in your muscle, liver and erythrocytes.
Forbes disease results from a deficiency of the enzyme amylo-1,6 glucosidase, or debrancher enzyme. This leads to excess amounts of abnormal glycogen being placed in your liver, muscles and, in some instances, your heart. There may also be deficiency in some of your blood cells, such as erythrocytes and leukocytes. About 15% of the time, Forbes disease only affects your liver.
The glycogen molecule is not a simple straight chain of linked glucose molecules. It is an intricate network of short chains that branch off from one another. In glycogenolysis, a certain enzyme is needed to unlink the branch points. Forbes disease results from the failure of that enzyme.
There are several different signs and symptoms of Forbes disease. These include:
- Delay of puberty
- Low blood sugar (hypoglycemia)
- Bones that are weakened by osteoporosis
- Elevated levels of lipids, uric acid and lactate in your blood
- Impairment in growth
- An enlarged fatty liver
- An enlarged heart
- Muscles that are prone to wasting
Muscle wasting usually increases with age, while other signs and symptoms may improve.
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