The
muscular dystrophies are a group of genetic and
hereditary muscle diseases; characterized by
progressive skeletal muscle weakness, defects in
muscle proteins, and the death of muscle cells
and tissue. In some forms of muscular dystrophy,
cardiac and smooth muscles are affected. The
muscular dystrophies are theon hereditary
diseases.
Cause
The
dystrophies are caused by mutations of genes
involved in muscle structure, with the gene for
the dystrophin protein being the most prominent
one. The dystrophin gene is located on the X
chromosome (Thus making it a 'sex-linked'
disorder). Accordingly, muscular dystrophies are
much more common in males, as females have two
copies of that chromosome, males have only one.
Types
The
major types of muscular dystrophy include:
-
Becker's muscular dystrophy
-
Congenital muscular dystrophy
-
Distal muscular dystrophy
-
Duchenne muscular dystrophy
-
Emery-Dreifuss muscular dystrophy
-
Facioscapulohumeral dystrophy
-
Fukuyama congenital muscular dystrophy (FCMD)
-
Limb-girdle muscular dystrophy
-
Myotonic muscular dystrophy
-
Oculopharyngeal muscular dystrophy
-
Severe childhood autosomal recessive muscular
dystrophy
Duchenne MD
is the most common form of muscular dystrophy
affecting children, and myotonic muscular
dystrophy is the most common form affecting
adults. Muscular dystrophy can affect people of
all ages. Although some forms first become
apparent in infancy or childhood, others may not
appear until middle age or later.
The most
frequent symptoms are muscle weakness (frequent
falls, walking problems, eyelid drooping),
skeletal and muscle deformities. Neurologic
examination often reveals loss of muscle tissue
(wasting), muscle contracture, pseudohypertrophy
and weakness.
Diagnosis is usually established
by muscle biopsy, elevated serum CK levels and
electromyography examination, which is
consistent with myogenic involvement. Some types
of muscular dystrophy may present with
additional cardiac disease, intellectual
deterioration and infertility. There is no known
cure for muscular dystrophy. Inactivity (such as
bedrest and even sitting for long periods) can
worsen the disease. Physical therapy and
orthopedic instruments (e.g. wheelchairs) may be
helpful.
Prognosis
The
prognosis of muscular dystrophy varies according
to the type of muscular dystrophy and the
progression of the disorder. Some cases may be
mild and very slowly progressive, with normal
lifespan, while other cases may have more marked
progression of muscle weakness, functional
disability and loss of ambulation. Life
expectancy may depend on the degree of
progression and late respiratory deficit. In
Duchenne muscular dystrophy, death usually
occurs in the late teens to early 20s, however
there are many young men living into the mid
30's. The use of mechanical ventilation and
heart medications have been shown to prolong
life in DMD.
