Myotonic disorders are a group of genetic conditions that affect muscle function, characterized by prolonged muscle stiffness or difficulty relaxing muscles after contraction. The most common type is myotonic dystrophy, which can also impact other systems in the body, including the heart and endocrine system. These disorders are caused by mutations in specific genes, leading to abnormal muscle function. Symptoms can vary widely among individuals, but they often include muscle weakness, cramps, and myotonia, which is the inability to relax muscles. Diagnosis typically involves genetic testing and muscle biopsies.