What Is Muscular Dystrophy?
Muscular dystrophy is a group of disorders characterized by a progressive loss of muscle mass and consequent loss of strength. The most common form of muscular dystrophy – Duchenne muscular dystrophy – typically affects young boys, but other variations can strike in adulthood.
Currently, there is no cure for muscular dystrophy, but certain physical and medical treatments can improve symptoms and slow the disease’s progression. Muscular dystrophy is a muscle-wasting disease whose predominant forms may affect up to 1 in every 5,000 males.
The condition is caused by genetic mutations that interfere with the production of muscle proteins necessary to build and maintain healthy muscles. The disease is genetic, and consequently, a history of muscular dystrophy in the family increases the chance of an individual developing the disease.
There are a number of muscular dystrophy types, including the following:
- Duchenne muscular dystrophy – the most common form of the illness. Symptoms normally start before a child’s third birthday; they are generally wheelchair-bound by 12 and die of respiratory failure by their early-to-mid-twenties.
- Becker muscular dystrophy – similar symptoms to Duchenne but with a later onset and slower progression; death usually occurs in the mid-forties.
- Myotonic (Steinert’s disease) – the myotonic form is the most common adult-onset form. It is characterized by an inability to relax a muscle once it has contracted. The muscles of the face and neck are often affected first. Symptoms also include cataracts, sleepiness, and arrhythmia.
- Congenital – this type can be obvious from birth or before the age of 2. It affects girls and boys. Some forms progress slowly whereas others can move swiftly and cause significant impairment.
- Facioscapulohumeral (FSHD) – onset can be at almost any age but is most commonly seen during teenage years. The muscular weakness often begins in the face and shoulders. People with FSHD may sleep with their eyes slightly open and have trouble fully closing their eyelids. When an individual with FSHD raises their arms, their shoulder blades protrude like wings.
- Limb-girdle – this variant begins in childhood or teenage years and first effects the shoulder and hip muscles. Individuals with the limb-girdle muscular dystrophy might have trouble raising the front part of the foot, making tripping a common problem.
- Oculopharyngeal muscular dystrophy – onset is between the ages of 40 and 70. Eyelids, throat, and face are first affected, followed by the shoulder and pelvis.
Muscular dystrophy is caused by mutations on the X chromosome. Each version of muscular dystrophy is due to a different set of mutations, but all prevent the body from producing dystrophin. Dystrophin is a protein essential for building and repairing muscles.
Duchenne muscular dystrophy is caused by specific mutations in the gene that encodes the cytoskeletal protein dystrophin. Dystrophin makes up just 0.002 percent of the total proteins in striated muscle, but it is an essential molecule for the general functioning of muscles.
Dystrophin is part of an incredibly complex group of proteins that allow muscles to work correctly. The protein helps anchor various components within muscle cells together and links them all to the sarcolemma – the outer membrane. If dystrophin is absent or deformed, this process does not work correctly, and disruptions occur in the outer membrane. This weakens the muscles and can also actively damage the muscle cells themselves.
In Duchenne muscular dystrophy, dystrophin is almost totally absent; the less dystrophin that is produced, the worse the symptoms and etiology of the disease. In Becker muscular dystrophy, there is a reduction in the amount or size of the dystrophin protein. The gene coding for dystrophin is the largest known gene in humans. More than 1,000 mutations in this gene have been identified in Duchenne and Becker muscular dystrophy.7
Duchenne muscular dystrophy, which represents about half of all cases of muscular dystrophy, affects about one in 5,000 males at birth. Muscular dystrophy was first described in the 1830s by Charles Bell. The word “dystrophy” is from the Greek dys, meaning “difficult” and troph meaning “nourish”. Gene therapy, as a treatment, is in the early stages of study in humans.