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Types of Muscular Dystrophies



Muscular dystrophies are a family of inherited (genetic) diseases that cause gradual wasting and weakening of muscles (and in some cases, of nerve tissue). In total, there are 9 types of generally accepted muscular dystrophies - each with its own characteristic age of onset, rate of progress etc - and the people affected by them are all characterized by muscle weakness, general difficulty in walking and sometimes deformities

The most common muscular dystrophy is Duchenne muscular dystrophy (DMD), followed by Becker muscular dystrophy (BMD). These two dystrophies feature the same kind of symptoms, and the diseases are inherited in the same way, although Duchenne MD is much more severe and debilitating. In fact, Becker MD is usually classified as a less severe form of Duchenne MD. They are both caused by a defect in the gene needed for the synthesis of a protein, called dystrophin, which is absolutely essential for the normal functioning of muscles. The result is that muscle fibers in affected patients are severely deficient in dystrophin (since the mutated version is not functional), which causes a decreased muscular function

Here's a list of the nine forms of muscular dystrophy:

Becker Muscular Dystrophy
  • Age of onset: 2 to 16 years
  • Symptoms: Similar to Duchenne MD, but less severe. They include general muscle weakness, especially in the upper leg and arms, and pelvic muscles. Calf muscles are generally hypertrophic (bigger than usual). Heart problems are also possible
  • Rate of Progression: Slower than Duchenne MD
  • Expected Lifespan: Well into middle age
  • Inheritance: X-linked recessive. BMD primarily affects young males, who inherit the disease through their mothers. Women can be carriers but usually exhibit no symptoms, because the dystrophin gene is located on the X chromosome - of which women have 2 copies - and one functioning copy of the dystrophin gene is generally sufficient for normal muscle function.
Congenital Muscular Dystrophy
  • Age of onset: Already present at birth
  • Symptoms: General muscle weakness and possible joint deformities. Depending on the type, it may involve scoliosis (spinal curvature), respiratory problems, mental retardation or learning disabilities, eye defects or seizures
  • Rate of Progression: Slow
  • Expected Lifespan: Varies, but is generally a bit shorter than normal people
  • Inheritance: Autosomal recessive or autosomal dominant; these diseases are sometimes inherited through both parents and sometimes inherited from one parent. They can also occur spontaneously because of a newly developed genetic mutation
Duchenne Muscular Dystrophy
  • Age of onset: 2 to 6 years
  • Symptoms: General and severe muscle weakness and wasting, beginning from the upper arms, upper legs and pelvis. Weakness eventually progresses to all voluntary muscles. Calf muscles are generally hypertrophic (bigger than usual)
  • Rate of Progression: Fast
  • Expected Lifespan: as much as 25 years, survival past the twenties is very rare
Distal Muscular Dystrophy
  • Age of onset: 40 to 60 years
  • Cause: A mutation in any of at least eight genes that affect proteins necessary to the function of muscles
  • Symptoms: Weakness and wasting of muscles of the hands, forearms, and lower legs
  • Rate of Progression: Slow
  • Expected Lifespan: Rarely leads to life-threatening situations
  • Inheritance: May be autosomal dominant, (a faulty gene is inherited from one parent); or autosomal recessive (when a faulty gene is inherited from both parents).
Emery-Dreifuss Muscular Dystrophy
  • Age of onset: childhood to early teens
  • Cause: Mutations in the genes that produce emerin, lamin A or lamin C, proteins in the membrane that surrounds the nucleus of each muscle cell.
  • Symptoms: wasting and weakness of shoulder, upper arm, and shin muscles. Often causes joint deformities and heart problems
  • Rate of Progression: Slow, often causes cardiac complications and may require a pacemaker.
  • Expected Lifespan: Due to this disease affecting cardiac muscle fibers, sudden death is possible because of cardiac complications
  • Inheritance: Can be X-linked recessive, primarily affecting males, who inherit the disease through their mothers. Another type is autosomal dominant, meaning it can be inherited through either parent; an autosomal recessive type occurs when a faulty gene is inherited from both parents.
Facioscapulohumeral Muscular Dystrophy
  • Age of onset: teens to early adulthood
  • Symptoms: facial muscle weakness and weakness with some wasting of shoulders and upper arms
  • Rate of Progression: Slow and not steady, interspersed with periods of rapid worsening
  • Expected Lifespan: usually many decades after onset
Limb-Girdle Muscular Dystrophy
  • Age of onset: late childhood to middle age
  • Symptoms: Muscle wasting and weakness, beginning from the shoulder girdle and pelvic girdle
  • Rate of Progression: Slow
  • Expected Lifespan: Varies, death is usually due to cardiac or respiratory complications
Myotonic Muscular Dystrophy
  • Age of onset: any age, but usually 20 to 40 years (although it can be present at birth in Type 1 congenital myotonic dystrophy)
  • Symptoms: General muscle weakness, myotonia (difficulty or total incapacity of relaxing a muscle at will after a contraction). Weakness begins in the muscles of the face, feet, neck and hands
  • Rate of Progression: Slow
  • Expected Lifespan: Varies a lot, but can be as much as 50 to 60 years
Oculopharyngeal Muscular Dystrophy
  • Age of onset: 40 to 70 years
  • Cause: A faulty gene for poly(A)-binding protein nuclear 1 (PABPN1), which is suspected to lead to production of extra chemical material that causes formation of clumps in the muscle cells.
  • Symptoms: Weakness in the muscles of the eye (drooping eyelids) and of the throat (accompanied generally by an inability to swallow, causing possible nutritional deficiencies and emaciation
  • Rate of Progression: Slow
  • Expected Lifespan: Varies
  • Inheritance: May be autosomal dominant, meaning OPMD is inherited from one parent; or autosomal recessive, occurring when a faulty gene is inherited from each parent.

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