Myotonia Congenita (CLCN1 gene, Miniature Schnauzer)

Myotonia congenita is a disease that affects skeletal muscles and is characterized by the inability of muscles to relax properly after contraction. This condition is the result of mutations that affect the functioning of the chloride channel in muscle cells.

Symptoms

Clinical signs described include generalized stiffness in movement, severe skeletal muscle hypertrophy and increased breath sounds. Other symptoms include difficulty in swallowing and excessive salivation (appears from 2-3 months of age). In some cases, a close relationship between myotonia congenita and upper prognathism has been observed in this breed.

Disease Management

No cure for myotonia congenita has been reported, however, affected dogs are usually kept stable with drug treatment, such as procainamide.

Genetic basis

This disease follows an autosomal recessive mode of inheritance. Autosomal recessive inheritance means that the dog, regardless of sex, must receive two copies of the mutation or pathogenic variant to be at risk of developing the disease. Both parents of an affected dog must carry at least one copy of the mutation. Animals with only one copy of the mutation are not at increased risk of developing the disease, but may pass the mutation on to future generations. Breeding between dogs carrying genetic variants that can cause disease, even if they do not show symptoms, is not recommended.

Technical report

Myotonia congenita is a disorder caused by mutations in the CLCN1 gene encoding a voltage-dependent chloride channel in skeletal muscle. Mutations in the gene cause the chloride channel to be unable to open fully and therefore depolarization lasts longer than usual. Consequently, skeletal muscle relaxation is delayed after muscle contraction. It has been discovered that in the Miniature Schnauzer breed there is a specific genetic mutation (c.803C>T) in the CLCN1 gene, which results in the replacement of the amino acid threonine by methionine. This mutation leads to a significant reduction in the opening capacity of the chloride channel at physiological voltage levels. As a result, muscle hyperexcitability and difficulty for the muscle to relax properly after contraction is observed.

Most affected breeds

  • Miniature Schnauzer

Bibliography

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