Glycogen Storage Disease Type X
What else is it called?
- Dimauro disease
- GSD X
- Human muscle phosphoglycerate mutase deficiency
- Myopathy due to phosphoglycerate mutase deficiency
- Glycogenosis type X
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What causes it?
The condition is caused by mutations (changes) in the PGAM2 gene. This gene is responsible for encoding (programming) the enzyme called phosphoglycerate mutase. This enzyme is found mainly in the skeletal muscle cells. The mutase is involved in the process of glycolysis (the breakdown of glucose by enzymes). Mutase helps in carrying out the chemical reaction that converts 3-phosphoglycerate (produced during the breakdown of glucose) into 2-phosphoglycerate.
Mutations (changes) in the PGAM2 gene greatly decreases mutase activity which disturbs the energy production in the skeletal muscle cells. This leads to muscle cramps, muscle breakdown and the other symptoms associated with glycogen storage disease type X.
How common is it?
Glycogen Storage Disease Type X is a very rare inherited condition. Less than 50 cases have been reported worldwide so far.
What are the signs and symptoms?
Signs and symptoms of this condition usually start in childhood or during adolescence and may include:
- Muscle pains or cramps after strenuous physical exercise
- Exercise intolerance
- Recurrent episodes of myoglobinuria (myoglobin in the urine)
- Kidney failure (if myoglobinuria is left untreated)
How is it diagnosed?
Diagnosis of this condition is usually started through a full medical history, physical exam and observation of symptoms.
Specialized urine tests can be done to detect myoglobin in the urine.
A diagnosis it confirmed through molecular genetic testing which will show mutations (changes) in the PGAM2 gene.
Can it be treated?
There are no specific treatments for GSD type Ia. Treatment for this condition is symptomatic and supportive. This aims to manage and alleviate individual symptoms such and to provide support for the patients and their families.
Do my family need to be tested?
Glycogen storage disease type X is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.
The pattern of inheritance of glycogen storage disease type X is autosomal recessive. This means that carriers of the condition do not have the disorder because the other gene of this pair is working normally. Parents of children with glycogen storage disease type X are carriers.
When both parents are carriers, the risk to the baby in each pregnancy is
- 25% chance (1 in 4) of developing the condition
- 50% chance (1 in 2) for the baby to be a carrier of the condition
- 25% chance (1 in 4) for the baby to have two working genes and neither have the condition nor be a carrier
Genetic counselling can be requested to get a full explanation.
For more information, please visit Association for Glycogen Storage Disease UK.