TYPES OF MUSCULAR DYSTROPHY
Muscular Dystrophies are a group of hereditary and non-hereditary disorders that primarily affect the striated muscles throughout the body. They are characterized by defects in muscle proteins and the death of muscle cells and tissue and progressive skeletal muscle weakness.
The absence of functional proteins results in destabilization of the muscle membrane, increased muscle fragility and degeneration, and progressive muscle wasting. Muscular dystrophy is usually broadly classified into nine types including Duchenne, Becker, limb girdle, congenital, facioscapulohumeral, myotonic, oculopharyngeal, distal and Emery-Dreifuss.
TYPES of MUSCULAR DYSTROPHY
There are nine types of muscular dystrophies. This group of genetically distinct disorders shares clinical and pathological characteristics but varies in age of onset, rate of progression, distribution of weakness, severity, inheritance pattern, and molecular defect.
1. Duchenne muscular dystrophy (DMD)
It is one of the most common and a rapidly-worsening form of muscular dystrophies, affecting 1 in 3,600 male births. Mutation in the dystrophin gene represents the primary cause of DMD. It is characterized by rapid progression of muscle degeneration wherein the muscle is ultimately replaced by fat.
2. Becker muscular dystrophy
It is also known as benign pseudohypertrophic muscular dystrophy which is an X-linked recessive inherited disorder characterized by slowly progressive muscle weakness of limbs. It affects about 1 in 30,000 males. Becker muscular dystrophy (BMD) is similar to Duchenne muscular dystrophy (DMD) but has a milder course. DMD patients lack functional dystrophin, whereas BMD patients have a reduced efficiency of the protein.
3. Limb-girdle muscular dystrophy (LGMD)
It is also known as Erb's muscular dystrophy which is an autosomal class of muscular dystrophy. The term "limb-girdle" is used to describe these disorders because the muscles most severely affected are generally those of the pelvic and shoulder girdle muscles. Prevalence of all the forms of LGMD range from 1 in 14500 to 1 in 123000.
4. Facioscapulohumeral muscular dystrophy (FSHMD, FSHD or FSH)
Also known as Landouzy-Dejerine, is the third most common genetic disease of skeletal muscle, an autosomal dominant disorder with incidence of 1 in 20,000. It initially affects the skeletal muscles of the face (facio), scapula (scapulo) and upper arms (humeral).
5. Oculopharyngeal Muscular Dystrophy
Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant disorder characterized by slowly progressive ptosis (drooping eyelids), dysphagia (difficulty in swallowing) and proximal limb weakness.
6. Emery- Dreifuss Muscular Dystrophy
Emery–Dreifuss muscular dystrophy (EDMD) is inherited either as an autosomal dominant form or an X-linked recessive disorder. The two forms are clinically very similar with a predominance of the X-linked form. Prevalence is estimated at 1 in 300,000.
7. Congenital muscular dystrophy (CMD)
It is the term used to describe muscular dystrophy that is present at birth. CMD describes a number of autosomal recessive diseases of muscle weakness and possible joint deformities, present at birth and slowly progressing. Life expectancies for affected individuals vary, although some forms of CMD do not affect life span at all.
8. Myotonic Muscular Dystrophy Myotonic dystrophy (MD)
is the most common form of adult-onset muscular dystrophy. It affects at least 1 in 8,000 people worldwide. There are currently two known types of MD; myotonic dystrophy type 1 (MD1), also known as Steinert disease and myotonic dystrophy type 2 (MD2), commonly referred to as PROMM or proximal myotonic myopathy.
9. Distal Muscular Dystrophy
The distal muscular dystrophy are a clinically and pathologically heterogeneous group of genetic disorders in which the distal muscles of the upper and the lower limbs are selectively or disproportionately affected.
Following are the types of distal muscular dystrophy
a. Welander’s distal muscular dystrophy:
b. Tibial distal muscular dystrophy:
c. Miyoshi distal muscular dystrophy:
d. Nonaka distal muscular dystrophy:
e. Gowers-Laing distal muscular dystrophy:
f. Hereditary inclusion-body myositis (myopathy) type 1 (HIBM1):
g. Distal muscular dystrophy with vocal cord and pharyngeal weakness:
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