RYR-1 muscle disease
Type of disease: Rare conditions
RYR-1 muscle disease refers to any muscle condition that is present at birth (congenital) and is caused by a mutation in the RYR-1 gene. Mutations in this gene are the most common cause of congenital myopathy (muscle weakness).
The RYR-1 gene, when functioning properly, is responsible for regulating the flow of calcium through the muscle. When the RYR-1 gene is changed due to an error (mutation), the calcium flow is impaired and causes abnormal muscle contractions as well as muscle weakness. Other symptoms such as breathing problems which may range from severe to non-existent, malignant hyperthermia (a potentially fatal reaction to anesthesia), muscle cramps and pains, inability to exercise, and heat intolerance have also been reported. Diagnosis of an RYR-1 muscle disease may be done through genetic testing, a muscle biopsy, or both. There is no cure for this condition, but research is underway.
RYR-1 muscle disease can be inherited in one of two ways from a parent who may or may not be affected. Sometimes an RYR-1 gene change is dominant which means that only one copy of the changed gene is needed to causes symptoms. In this case, an affected individual will have a 50% chance of passing on the gene change, and therefore the condition, to each of their children. In autosomal recessive inheritance, both copies of the gene must be changed for the person to have the condition and each of their children has a 25% chance of inheriting the gene change and therefore the condition. A genetic counselor can provide a better understanding of the inheritance and risks to future pregnancies.