Glycogen Storage Diseases

Glycogen storage diseases are inherited conditions in which there is an inability of the body to store and metabolize glycogen efficiently leading to frequent episodes of low blood sugar, muscle weakness, and can also lead to liver damage. There are a lot of enzymes that are involved in the formation and storage of glycogen and these diseases occur when the enzymes are missing.

Types of Glycogen Storage Diseases

Type 1- Von Gierke’s disease (the enzyme defect is glucose 6 phosphatase)

Type 2- Pompe’s disease (the enzyme defect is acid maltase/ acid glucosidase)

Type 3- Cori’s disease (the enzyme defect is debranching enzyme)

Type 4- Anderson’s disease (the enzyme defect is branching enzyme)

Type 5- McArdle’s disease (the enzyme defect is muscular phosphorylase)

Type 6- Her’s disease (the enzyme defect is Hepatic phosphorylase)

Type 7- Tarui’s disease (the enzyme defect is Phosphofructokinase- 1)

                        Glycogen metabolism

Type 1- Von Gierke’s Disease

• The main feature of type 1 glycogen storage disorder is hypoglycemia which does not respond to counter-regulatory hormones.
• There is a deficiency of an enzyme called glucose 6 phosphatase.
• Glucose 6 phosphatase deficiency leads to the accumulation of glucose 6 phosphate which will enter the glycolysis and gets converted into acetyl coenzyme A leading to the accumulation of fatty acids cholesterol and triglycerides. These triglycerides will accumulate in adipose tissue leading to doll-like facies.
• Cholesterol accumulation causes xanthoma and excess of pyruvate will convert into lactate causing lactic acidosis.

Clinical Presentations

• Hypoglycemia
• Doll like facies
• Xanthomas
• Ketosis
• Lactic acidosis
• Hyperuricemia
• Hepatomegaly

Also Read: Phenylketonuria: Symptoms, Causes and Treatment

Type 2 Pompe’s disease

• This is the only lysosomal storage disorder along with glycogen storage disorder and the enzyme involved is acid maltase or alpha-glucosidase enzyme.
• It occurs in cardiac and skeletal muscle.

Clinical Manifestations

• Cardiomegaly
• Cardiomyopathy
• Hypotonia
• Floppy baby
• Respiratory distress and failure to thrive

Also Read: Gaucher Disease: Causes, Symptoms, Risk Factors, Diagnosis, Treatment and Complications

Type-3 Cori’s Disease

• Type 3 glycogen storage disorder is caused by a deficiency of the debranching enzyme.
• There will be the presence of hypoglycemia and the patient will present with exercise intolerance.
• The deep branching enzyme breaks branched glycogen into glucose and makes it available to use when the body needs glucose but in this disease the debranching enzyme is unavailable hence patient will feel hypoglycemia.

Clinical Manifestations

• Cardiomyopathy
• Hyperglycemia
• Normal blood lactate levels
• Exercise intolerance

Also Read: Amino Acid Disorders

Type 4  Anderson’s Disease

• Type 4 glycogen storage disease is caused by a defect in the branching enzyme.
• The unique point about this storage disorder is there will be neither hyperglycemia and nor exercise intolerance.
• It mainly presents as hepatosplenomegaly and failure to thrive in early infancy.

Clinical Manifestations

• Infantile cirrhosis
• Hypotonia
• Muscle weakness
• Hypoglycemia can occur late in the disease

Also Read: All Important Things About Carbohydrate Metabolism

Type 5 McArdle’s disease

• In this glycogen storage disorder there is a deficiency of muscle phosphorylase enzyme.
• The patient will present with exercise intolerance.
• Due to deficiency of skeletal muscle glycogen phosphorylase the glycogen will build up in muscle and that will lead to painful muscle cramps.

Clinical Manifestations

• Muscle cramps 
• Myoglobinuria with strenuous exercise
• Arrhythmia due to electrolyte abnormalities
• There will be no hypoglycemia

Also Read: Enzymes Classification, Properties

Type 6- Her’s disease

• There is a deficiency of an enzyme called hepatic phosphorylase.
• The patient will experience hypoglycemia which doesn’t respond to counter-regulatory hormones.

Also Read: Amino Acids (Basic, Acidic), Transamination & Proteins

Type 7- Tarui’s disease

• It is caused by a deficiency of an enzyme called phosphofructokinase.
• The patient will present with exercise intolerance.
• There will also be the presence of hemolytic anemia.

Also Read: Fat Soluble Vitamins

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