Congenital Myotonia

Myotonia congenita is an inherited disease that hinders proper muscle relaxation after contraction. This condition is due to a mutation in the CLCN1 gene, which encodes chloride channels essential for normal muscle excitability. Affected cats have muscle stiffness and difficulty moving.

Symptoms

Affected cats often exhibit marked muscle hypertrophy, and when struck, dimpling may be noted in places such as the back and limbs. Their gait is stiff and short-stepping, accompanied by restricted limb adduction. In addition, they may experience episodes of muscle stiffness and sudden falls, particularly in response to stimuli such as startle. Other signs include difficulty opening the jaw, halitosis, swollen gums, involuntary facial movements, swallowing problems and an excessively protruding tongue.

Disease Management

Management of the condition focuses on improving quality of life and minimizing associated symptoms. Avoidance of stress triggers that can lead to episodes of muscle stiffness and falls is recommended. Medications such as muscle relaxants may be administered to reduce the frequency and intensity of muscle spasms.

Genetic basis

This disease follows an autosomal recessive mode of inheritance. Autosomal recessive inheritance means that the cat, 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 cat 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 cats carrying genetic variants that may cause disease, even if they do not show symptoms, is not recommended.

Technical report

Myotonia congenita is a condition characterized by the inability of muscles to relax normally after contraction, resulting in muscle stiffness. In cats, this disease has been linked to mutations in the CLCN1 gene, which encodes the chloride channel ClC-1. This channel allows the passage of chloride ion across the cell membrane, which is essential for maintaining the resting potential of the muscle cell and regulating muscle excitability. In a recent study, a mutation was identified in an intronic splice site of the CLCN1 gene. This mutation causes the loss of two exons and the absence of 116 amino acids in the CLCN1 protein, compromising its ion channel function.

Most affected breeds

Domestic

Bibliography

Gandolfi B, Daniel RJ, O'Brien DP, et al. A novel mutation in CLCN1 associated with feline myotonia congenita. PLoS One. 2014 Oct 30