Summary about Disease
Glycogen storage disease type III (GSD III), also known as Cori disease or Forbes disease, is a rare genetic disorder that affects the way the body breaks down glycogen. Glycogen is a stored form of glucose (sugar), which the body uses for energy. In GSD III, a deficiency in the enzyme amylo-1,6-glucosidase (debrancher enzyme) prevents the complete breakdown of glycogen. This leads to an accumulation of abnormal glycogen in the liver, muscles, and sometimes other tissues. The severity and specific symptoms vary considerably among affected individuals.
Symptoms
Symptoms of GSD III can vary in severity and age of onset, but commonly include:
Infancy/Childhood:
Hepatomegaly (enlarged liver)
Hypoglycemia (low blood sugar), especially after periods without eating
Growth retardation
Abdominal distension
Muscle weakness (myopathy)
Adulthood (in some cases):
Liver cirrhosis (scarring of the liver)
Muscle weakness that may worsen
Cardiomyopathy (enlarged heart)
Causes
GSD III is caused by mutations in the AGL gene. This gene provides instructions for making the amylo-1,6-glucosidase enzyme, also known as the debrancher enzyme. These mutations lead to a deficiency or absence of the functional enzyme, preventing the complete breakdown of glycogen. GSD III is inherited in an autosomal recessive pattern, meaning that both parents must carry a copy of the mutated gene for a child to be affected.
Medicine Used
There is no specific cure for GSD III, but management focuses on controlling symptoms and preventing complications. Treatment strategies include:
Dietary Management: Frequent feedings or snacks high in protein can help maintain stable blood sugar levels and reduce glycogen accumulation. Uncooked cornstarch may be used to provide a slow release of glucose, particularly at night. High-protein diets are often recommended.
Medications: In some cases, medications may be used to manage specific complications such as liver or heart problems.
Liver Transplantation: In rare instances of severe liver disease, liver transplantation may be considered.
Is Communicable
No, GSD III is not communicable. It is a genetic disorder caused by a gene mutation and cannot be spread from person to person.
Precautions
Precautions for individuals with GSD III mainly involve careful dietary management and regular monitoring for complications. Key precautions include:
Adhering to the prescribed dietary plan: Following the recommended diet of frequent, high-protein meals and snacks is crucial.
Avoiding prolonged fasting: Periods without eating should be minimized to prevent hypoglycemia.
Regular medical check-ups: Monitoring liver function, muscle strength, and heart health is important for early detection and management of any complications.
Emergency preparedness: Having a plan in place to address hypoglycemia, including readily available sources of glucose (e.g., glucose gel or tablets).
How long does an outbreak last?
GSD III is not an infectious disease and does not involve outbreaks. It is a chronic condition that requires ongoing management throughout a person's life.
How is it diagnosed?
Diagnosis of GSD III typically involves a combination of:
Clinical Evaluation: Assessment of symptoms, medical history, and family history.
Laboratory Tests:
Blood tests: To measure blood glucose, liver enzymes, creatine kinase (CK), and other markers.
Urine tests: Ketone levels may be measured.
Glycogen content and enzyme activity assay: A liver or muscle biopsy can be used to measure glycogen content and debrancher enzyme activity.
Genetic Testing: AGL gene sequencing can confirm the diagnosis by identifying mutations.
Imaging Studies: Ultrasound or MRI may be used to assess liver size and structure.
Timeline of Symptoms
The timeline of symptoms can vary, but a general progression is as follows:
Infancy/Early Childhood:
Hepatomegaly is often the first noticeable sign.
Hypoglycemia may occur, especially with prolonged fasting.
Growth may be slower than expected.
Childhood/Adolescence:
Muscle weakness may become apparent.
Liver enlargement may persist, and liver enzyme levels may be elevated.
Adulthood (in some individuals):
Liver cirrhosis may develop.
Cardiomyopathy can occur.
Muscle weakness may worsen.
Important Considerations
Genetic Counseling: Families with GSD III should consider genetic counseling to understand the risk of recurrence in future pregnancies.
Lifelong Management: GSD III requires lifelong management and monitoring.
Individual Variability: The severity and progression of GSD III can vary significantly among individuals.
Nutritional Guidance: Working closely with a registered dietitian experienced in managing GSD is essential for developing an appropriate dietary plan.
Coordination of Care: Management often involves a team of specialists, including a gastroenterologist, endocrinologist, cardiologist, and geneticist.