Muscular Dystrophy
Skeletal Muscle Disorder: Muscular Dystrophy
Muscular dystrophy (MD) is a group of inherited genetic disorders that result in progressive deterioration of skeletal muscles because of mixed muscle cell hypertrophy, atrophy, and necrosis.
The MDs make up the largest and most common group of inherited progressive neuromuscular disorders of childhood. They affect all population types, including animals.
Muscular dystrophies, in general, have a genetic origin and are characterized by ongoing, typically symmetric, muscle wasting with increasing deformity and disability.
Paradoxically, in some forms (e.g., Duchenne’s, Becker’s) wasted muscles tend to hypertrophy because of connective tissue and fat deposits.
As the muscle undergoes necrosis, fat and connective tissue replace the muscle fibers, which increases muscle size, giving the visual appearance of muscle strength, but actually yielding in muscle weakness.
The increase in muscle size resulting from connective tissue infiltration is called pseudohypertrophy Opens in new window. The muscle weakness Opens in new window is insidious in onset but continually progressive, varying with the type of disorder.
Duchenne muscular dystrophy (DMD) is the most common form of the disease, affecting one in every 3,500 live male births.
DMD Opens in new window is inherited as a recessive single-gene defect Opens in new window on the X chromosome Opens in new window and is transmitted from the mother to her male offspring. Because DMD is an X-linked recessive disorder, most carrier females are asymptomatic.
Another form of muscular dystrophy, Becker muscular dystrophy (BMD) Opens in new window, is similarly X-linked but manifests later in childhood or adolescence and has a slower course or progression.
Other common forms of dystrophies are summarized in Table X1.
| Table X1 | Summary of Nine Types of Muscular Dystrophy | ||||
|---|---|---|---|---|
| Type of Muscular Dystrophy | Inheritance Pattern | Age of Onset | Type of Muscle Affected | Rate of Progression |
| Becker muscular dystrophy (BMD) | X-linked recessive | Childhood to adulthood | Less severe form of DMD | Slower then DMD |
| Table X1 Continues | ||||
|---|---|---|---|---|
| Type of Muscular Dystrophy | Inheritance Pattern | Age of Onset | Type of Muscle Affected | Rate of Progression |
| Congenital muscular dystrophy (CMD) | Autosomal recessive or dominant or de novo | At or near birth | General muscle weakness | Mainly slow but varies with type |
| Duchenne muscular dystrophy (DMD) | X-linked recessive | Early childhood | General muscle weakness, proximal greater than distal | Usually slow |
| Distal muscular dystrophy (DD) | Autosomal dominant or recessive | Childhood to adulthood | Hands, forearms, calf | Slow |
| Emery-Dreifuss muscular dystrophy (EDMD) | X-linked recessive or autosomal dominant | Childhood to early adolescence (usually by age 10) | Shoulder, upper arm, calf | Slow; sudden death may occur due to cardiac problems |
| Facioscapulohumeral muscular dystrophy (FSH or FSHD) | Autosomal dominant or de novo | Adolescence to early adulthood (usually by age 20) | Eyes & mouth, shoulders, upper arms, and calf initially, then abdominal & hip | Slow, with periods of rapid deterioration |
| Limb-girdle muscular dystrophy (LGMD) | Autosomal dominant or recessive | Childhood to adulthood | Shoulder & pelvic girdles (limb) initially | Slow |
| Myotonic muscular dystrophy (MMD) | Autosomal dominant | Congenital form at birth, or adolescence to adulthood | Face, calf, forearms, hands, and neck initially; gastrointestinal, vision, cardiac, or respiratory complications later | Slow |
| Table X1 Continues | ||||
|---|---|---|---|---|
| Type of Muscular Dystrophy | Inheritance Pattern | Age of Onset | Type of Muscle Affected | Rate of Progression |
| Oculopharyngeal muscular dystrophy (OPMD) | Autosomal dominant or recessive | Adulthood (usually forties or fifties) | Eyelids & throat initially, facial and limb later | Slow |
| From Muscular Dystrophy Association. (2006). Diseases in the MDA program, master list. | ||||
See also:
- Williams, O. (2007). Diseases of muscle. In Brust, J.M.C. (Ed.), Current Diagnosis and Treatment in Neurology. New York: McGraw-Hill.
- Muntoni, F., Torelli, S., & Ferlini, A. (2003). Dystrophin and mutations: One gene, several proteins, multiple phenotypes. Lancet Neurology, 2, 731-740.
- Do, T. (2002). Orthopedic management of the muscular dystrophies. Curr Opin Pediatr, 14, 50-53.
