The brain is able to control the actions of skeletal (voluntary) and smooth (involuntary) muscles by sending signals that stimulate muscles to contract or relax. Genetic neuromuscular disorders disrupt this system. Some of these disorders are X-linked, which means men are more likely to have them because they only have one X-chromosome. Others are autosomal dominant which means only one mutated gene is needed, or autosomal recessive, meaning both parents must pass on a mutated gene for the disorder to occur.
Dystrophies
Muscular dystrophies are a class of genetic neuromuscular diseases that lead to progressive loss of muscle tissue and weakness over time. According to the Muscular Dystrophy Association, there are a number of different types of muscular dystrophy with each type having a different genetic mutation and causing weakness of different areas of the body. Examples of muscular dystrophies include Duchenne's and Becker's (weakness of the hips, pelvis, shoulders and thighs), Emery-Dreifuss (upper arm, shoulder, calf and heart), Limb-Girdle (shoulders and hips) and Oculopharyngeal (weakness of eyelids and throat).
Myopathies
Myopathies describe genetic neuromuscular diseases that, according to National Institute of Neurological Disorders and Stroke (NINDS) result in weakness of specific muscles but without loss of muscle tissue. Congenital myopathies typically cause symptoms early in infancy as the baby appears "floppy" as a result of weakened muscles. The NINDS notes that there are seven different kinds of congenital myopathies: myotubular, nemaline, hyaline body, central core disease, centronuclear, multi-minicore disease and congenital fiber-type disproportion myopathy.
Myotonia
Myotonia describes a less severe type of neuromuscular disorder which is distinguished not by muscle weakness but by difficulty in getting muscles to relax after a voluntary contraction or electrical stimulation. Patients with this kind of neuromuscular disorder can have a stiff gait, trouble rising from a sitting position, or may struggle to release things from their grasp. This kind of disease can be caused by specific genetic disorders called channelopathies, which are genetic abnormalities that affect how cells transport molecules such as potassium and calcium. Myotonia typically can be improved by "warming up" the muscles, and is exacerbated by cold.
