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Glycogen Storage disease: Type 3
Monday, 03 November 2003
Monday, 29 November 2004
Cori Disease, Amylo-1, 6-glucosidase deficiency, Debrancher deficiency, Glucogenesis type III

What

: Glycogen Storage Disease type 3 (GSD 3) is an inherited metabolic disease which is characterized by an enlarged liver, muscle weakness, low blood sugar and growth delay. These problems result from a defect in an enzyme called amylo-1, 6-glucosidase, which is needed for the proper conversion of glycogen into glucose. There are two types of GSD3, type a and b. GSD3a involves both the liver and muscle, whereas GSD3b only affects the liver.

Who

The incidence is about 1 in 400,000 births, equally prevalent in males and females.

Signs and Symptoms

Children affected with GSD3 may have a swollen abdomen, which is due to an enlarged liver, and weak muscles. Food is converted into glucose in the body and stored in the liver and muscles in the form of glycogen when it is not being used for energy. In GSD3, this stored glycogen accumulates in the liver causing it to enlarge. Because children with GSD3 cannot release their stored glycogen, they may develop low blood sugar levels, especially if they do not eat regularly. They are also known to have growth delay, low muscle tone, muscle weakness, obesity and a tendency to bleed easily. There is an infantile form of GSD3 (Type 1), as well as a juvenile form (Type 2). Type 1 happens in the first few months of life, and includes an enlarged liver, low blood sugar levels, low muscle tone and muscle weakness with poor control of the head. Type 2 includes an enlarged liver, muscle tone that is more normal during childhood but becomes poorer later in life, and a heart that is more normal during childhood but may become enlarged in size during adulthood.

Possible Causes

All of us have genetic material that makes us who we are. The genetic material referred to as “chromosomes” are numbered. The gene for GSD3 has been found on chromosome 1 called the AGL gene. Mistakes in this gene cause GSD3. GSD3 is an autosomal recessive genetic disorder. This means that each parent has one abnormal gene and one normal gene on chromosome 1. Because each parent has one normal gene, they themselves do not have GSD3. However, when the child receives one abnormal gene from each of the parents, the child has two affected genes on chromosome 1. In autosomal recessive diseases, when a person has two abnormal genes, they are affected with disease; in this case, GSD3. After a meal is eaten, the carbohydrates (sugars) from that meal are released into the bloodstream in the form of glucose. Glucose is what the body uses for energy. The extra glucose that the body does not need right away is stored in the liver in the form of glycogen. This glycogen is “stored fuel” for the body. In normal people, if extra energy is needed in the future, glycogen is released from the liver into the bloodstream in the form of glucose. An important enzyme, called amylo-1, 6-glucosidase, helps to change glycogen into glucose. If this enzyme is missing, as is the case for GSD3, the body has no way of releasing its stored fuel. This causes a buildup of unusable glycogen in places that store it, such as the liver and muscle. When a person has not eaten and there is no glucose for energy, problems may start. Because there is no enzyme to change glycogen into glucose, glucose levels may become low and the child starts showing the symptoms described above.

Diagnosis

GSD3 may be suspected when the above signs and symptoms, including a large liver, are found on physical examination. Blood testing usually shows low blood sugar, high levels of fat and glycogen, and a deficiency in amylo-1, 6-glucosidase. Removing a piece of the liver or muscle (called a biopsy) to analyze it would show inflammation with large levels of abnormally structured glycogen. The diagnosis can be confirmed with genetic testing to find the gene mutation on chromosome 1.

Treatment

Children should be followed with a nutritionist or dietician who specializes in metabolic disorders. Treatment consists of frequent feedings to make sure that the blood sugar levels don’t get too low. This may include feedings overnight through a tube that is placed from the nose to the stomach (nasogastric tube) so that the sugar levels do not get too low while the child is sleeping.

Prognosis

The prognosis for children with this disorder is very good because it does not affect life expectancy. The liver tends to return to a normal size during puberty, and the child tends to reach a normal height during late adolescence. The only problems that adults with type 3a might encounter are muscle disorders.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.

Weblinks

Association for Glycogen Storage Disease:
A great and informative website. It has a lot of information for families wanting to know more about this disorder, as well as helpful links, an email mailing list, and information on how to join the organization.

CLIMB
CLIMB (children living with inherited metabolic disorders) is a great website for families. It provides information about ongoing research and many different opportunities for creating support networks for children and parents affected by the disease.

Emedicine:
A very complex and detailed article on the disease. It has a lot of information, and can be hard to follow due to the complex medical terminology used.

Google Search for Glycogen Storage disease: Type 3

References and Sources

General Practice Notebook: www.gpnotebook.co.uk/simplepage.cfm?ID=-1207566294 Association for Glycogen Storage Disease: www.arsdus.org/ www.emedicine.com/ped/topic479.htm www.icondata.com/health/pedbase/files/FORBESDI.HTM