SNP Shot: Genomic Insights

Myotonia congenita is a condition impacting skeletal muscles, which are responsible for movement. Individuals with this disorder typically begin experiencing episodes of prolonged muscle contraction (myotonia) in childhood, making it difficult for their muscles to relax. While myotonia can affect any skeletal muscle, including those in the face and tongue, it commonly affects the legs. The resulting muscle stiffness can impair movement. The severity of stiffness varies among individuals, ranging from mild to severe enough to hinder walking, running, and daily activities. These muscle issues are often most apparent after a period of rest. Many individuals find that repeating movements can temporarily reduce muscle stiffness, a phenomenon referred to as the "warm-up effect."

Thomsen disease and Becker disease are the two main types of myotonia congenita. These conditions are differentiated by the intensity of their symptoms and how they are inherited. Becker disease typically manifests later in childhood than Thomsen disease and results in more pronounced muscle stiffness, especially in males. Individuals with Becker disease frequently experience short-term episodes of muscle weakness, primarily in the arms and hands, triggered by movement following periods of inactivity. They may also gradually develop a mild, permanent muscle weakness, which is not observed in those with Thomsen disease.

Inheritance:

The two types of myotonia congenita are passed down through different inheritance patterns. Thomsen disease follows an autosomal dominant inheritance pattern, indicating that only one copy of the altered gene in each cell is enough to cause the condition. Generally, a person with Thomsen disease has one parent who also has the condition. Becker disease follows an autosomal recessive inheritance pattern, which means that both copies of the gene in each cell must have mutations for the condition to develop. Most often, the parents of someone with Becker disease each carry one copy of the mutated gene, but they do not exhibit any signs or symptoms of the condition. Because different CLCN1 mutations can lead to either Becker disease or Thomsen disease, doctors usually distinguish between the two types of myotonia congenita based on their distinctive signs and symptoms.