From the Research
Myotonia congenita, also known as Thomsen disease, is a rare genetic disorder characterized by muscle stiffness and delayed muscle relaxation after voluntary contraction, caused by mutations in the CLCN1 gene, which encodes the chloride channel in skeletal muscle membranes. This condition is inherited as either autosomal-dominant or -recessive, known as Thomsen and Becker diseases, respectively, with Becker disease usually appearing later in childhood and causing more severe muscle stiffness and pain 1. The two forms of the disease, Thomsen and Becker, are distinguished by the severity of their symptoms and their patterns of inheritance, with mutations in the CLCN1 gene being the underlying cause of both types 2.
Some key aspects of myotonia congenita include:
- It is a genetic muscle disorder characterized by clinical and electrical myotonia, muscle hypertrophy, and stiffness 1
- Mutations in the muscular voltage-dependent chloride channel gene (CLCN1) have been found in both Thomsen and Becker diseases 1
- The disorder may be transmitted as either an autosomal-dominant or recessive trait with close to 130 currently known mutations 3
- Myotonia congenita is a specific inherited disorder of muscle membrane hyperexcitability caused by reduced sarcolemmal chloride conductance due to mutations in CLCN1 3
According to the most recent study, the management of myotonia congenita involves lifestyle modifications, and medications such as mexiletine and lamotrigine have been shown to be effective in treating myotonia 4. Additionally, genetic counseling is important for family planning, and physical therapy may help maintain muscle function. While myotonia congenita is not progressive or life-threatening, proper management significantly improves quality of life by reducing muscle stiffness and improving mobility. Patients should avoid triggers like cold temperatures, sudden movements, and potassium-rich foods which can worsen symptoms.
In terms of treatment, mexiletine is a commonly used medication, starting at 150-200mg three times daily, adjusting as needed, and other medications such as phenytoin, carbamazepine, or acetazolamide may also be used 5, 4. However, more work is needed to develop more targeted genetic treatments, and the pathogenicity of different variants can be determined using heterologous expression systems to understand the alteration in channel properties and predict the likelihood of causing disease 4.