Myotonia congenita

Myotonia Congenita is a neuromuscular disorder characterized by the slow relaxation of the muscles after voluntary contraction or electrical stimulation. This condition is present from early childhood, but symptoms can be mild. Myotonia Congenita is caused by mutations in the CLCN1 gene and can be inherited in an autosomal dominant or autosomal recessive manner.

Signs and Symptoms

The hallmark of Myotonia Congenita is muscle stiffness (myotonia) that worsens after periods of rest and improves with repeated use of the affected muscles (the "warm-up" effect). Other symptoms can include muscle weakness, pain, and enlargement (hypertrophy). The severity of the symptoms can vary widely among affected individuals, even among members of the same family.

Causes

Myotonia Congenita is caused by mutations in the CLCN1 gene. This gene provides instructions for making a protein that is critical for the normal function of skeletal muscle cells. The CLCN1 protein forms a channel that controls the flow of negatively charged chloride ions into these cells. This ion flow is necessary for the muscle cells to return to a relaxed state after they contract. Mutations in the CLCN1 gene reduce the flow of chloride ions, which makes the muscle cells overly excitable and leads to the prolonged muscle contractions seen in Myotonia Congenita.

Diagnosis

The diagnosis of Myotonia Congenita is based on the clinical symptoms, the family history, and specialized tests that evaluate muscle function. These tests can include electromyography (EMG), which measures the electrical activity of muscle cells, and genetic testing to identify mutations in the CLCN1 gene.

Treatment

There is currently no cure for Myotonia Congenita, but the symptoms can often be managed with medication. Drugs that are commonly used include mexiletine, phenytoin, and carbamazepine, which help to reduce muscle stiffness. Physical therapy can also be beneficial.

See Also

• Neuromuscular disease
• Muscular Dystrophy
• Genetic disorder

References

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