Summary about Disease
Glycogen synthase deficiency (GSD 0) is a very rare genetic metabolic disorder in which the body cannot properly store glucose as glycogen in the liver and muscle tissues. This is due to a deficiency of the enzyme glycogen synthase. It primarily affects the liver (hepatic form) or the muscles (muscle form), leading to problems with blood sugar regulation and energy production. The hepatic form is more common and leads to hypoglycemia. The muscle form leads to muscle fatigue and cramps after exercise.
Symptoms
Hepatic Form:
Hypoglycemia (low blood sugar), especially after fasting.
Hyperketonemia (high levels of ketones in the blood) during fasting.
Fatigue.
Poor growth in children.
Irritability.
Seizures (in severe cases of hypoglycemia).
Elevated liver enzymes may be seen during episodes.
Muscle Form:
Muscle cramps and fatigue during exercise.
Myoglobinuria (presence of myoglobin in the urine) after exercise.
Causes
Glycogen synthase deficiency is caused by mutations in the GYS1 gene (for the muscle form) or the *GYS2* gene (for the liver form). These genes provide instructions for making the glycogen synthase enzyme. The disease is inherited in an autosomal recessive pattern, meaning that both parents must carry a copy of the mutated gene for their child to be affected.
Medicine Used
There is no specific medicine that can cure glycogen synthase deficiency. Treatment focuses on managing the symptoms and preventing hypoglycemia and muscle damage. Dietary management is the primary treatment.
Dietary Management:
Frequent meals high in protein and complex carbohydrates.
Avoidance of prolonged fasting.
Uncooked cornstarch administration (especially before bedtime) to provide a slow release of glucose.
In severe cases, a continuous overnight gastric infusion of glucose may be necessary.
Is Communicable
No, glycogen synthase deficiency is not communicable. It is a genetic disorder and cannot be spread from person to person.
Precautions
Strict adherence to dietary recommendations.
Regular monitoring of blood glucose levels.
Avoiding strenuous exercise in the muscle form without proper management.
Education of family members, school personnel, and other caregivers about the condition and how to manage hypoglycemic episodes.
Wearing a medical identification bracelet or carrying a card that indicates the condition.
How long does an outbreak last?
Glycogen synthase deficiency is not an "outbreak" in the traditional sense. It is a chronic condition. Individual episodes of hypoglycemia or muscle cramping can last for a few minutes to several hours, depending on the severity and how quickly it is treated. The overall condition is lifelong.
How is it diagnosed?
Blood Tests:
During fasting, blood tests may reveal hypoglycemia and hyperketonemia.
Liver function tests may show elevated liver enzymes.
Urine Tests:
Urine may be tested for ketones and myoglobin.
Genetic Testing:
Definitive diagnosis is made by genetic testing of the GYS1 or *GYS2* gene to identify mutations.
Liver Biopsy (Rarely):
In the past, a liver biopsy was sometimes performed to measure glycogen synthase activity. This is rarely done now due to the availability of genetic testing.
Muscle Biopsy (for Muscle Form):
Muscle biopsy may be used in cases of the muscle form to assess glycogen content and enzyme activity.
Timeline of Symptoms
Infancy/Early Childhood (Hepatic Form): Symptoms often appear in infancy or early childhood with episodes of hypoglycemia, especially after overnight fasting or between meals. Poor growth may also be observed.
Childhood/Adolescence (Muscle Form): Symptoms typically manifest during childhood or adolescence with muscle cramps and fatigue during exercise.
Lifelong: The condition is lifelong, but symptoms can be managed with dietary modifications and lifestyle adjustments. The symptoms' intensity can vary based on adherence to treatment.
Important Considerations
Early diagnosis and management are crucial to prevent severe complications like seizures from hypoglycemia or permanent muscle damage.
A multidisciplinary approach involving a metabolic specialist, nutritionist, and genetic counselor is recommended.
Patients and families need comprehensive education about the condition, dietary management, and emergency procedures for hypoglycemic episodes.
For the muscle form, proper exercise planning is essential to avoid overexertion and muscle damage.
Genetic counseling is important for families with a history of glycogen synthase deficiency to understand the risk of recurrence.