This may be partly because there are over 130 currently known different mutations that can cause the disorder, each with their own specifics, and also because myotonia congenita is an ion channel disorder, and ion channels are sensitive to internal and external environmental factors. It has been shown that pregnancy and the use of diuretics aggravate myotonia, and both these conditions are linked to the loss of divalent cations such as magnesium and calcium. It has further been shown that in chemically-induced myotonia in isolated rat muscle, myotonia could be dampened by increasing the magnesium and calcium content of the extracellular medium. This has also been shown for isolated human muscle.Adrenaline/epinephrine is well known to make myotonia worse in most individuals with the disorder, and a person with myotonia congenita may experience a sudden increase in difficulty with mobility in a particularly stressful situation during which adrenaline is released.Due to the invisible nature of the disorder, the fact that those with myotonia congenita often appear very fit and able bodied, the general lack of knowledge about the disorder by the general and medical community, and often by the individual themselves, and the potential for inconsistency with the symptoms, many people with myotonia congenita have experienced a degree of social persecution at one time or another because of the effects of their disorder.
Myotonia congenita is a congenital neuromuscular channelopathy that affects skeletal muscles (muscles used for movement). It is a genetic disorder. The hallmark of the disease is the failure of initiated contraction to terminate, often referred to as delayed relaxation of the muscles (myotonia) and rigidity. Symptoms include delayed relaxation of the muscles after voluntary contraction (myotonia), and may also include stiffness, hypertrophy (enlargement), transient weakness in some forms of the disorder (from certain genetic mutations), severe masseter spasm, and cramping. The condition is sometimes referred to as fainting goat syndrome, as it is responsible for the eponymous fainting seen in fainting goats when presented with a sudden stimulus. Of note, myotonia congenita has no association with malignant hyperthermia (MH). Symptoms and signs
The prolonged muscle contractions, which occur most commonly in the leg muscles in recessive mutations, and more commonly in the hands, face, and eyelids in dominant mutations, are often enhanced by inactivity, and in some forms are relieved by repetitive movement known as "the warm-up effect". This effect often diminishes quickly with rest. Some individuals with myotonia congenita are prone to falling as a result of hasty movements or an inability to stabilize themselves after a loss of balance. During a fall, a person with myotonia congenita may experience partial or complete rigid paralysis that will quickly resolve once the event is over. However, a fall into cold water may render the person unable to move for the duration of submergence.