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Myotonia Congenita
(Two Forms: Thomsen's and Becker's Disease)
Usual Age of Onset
Early childhood
Disease Characteristics
Muscle stiffness and cramps after periods of rest.
Condition causes discomfort but is not life-threatening.
Inheritance
Becker: autosomal recessive, or produced by
defective genes contributed by both parents;
Thomsen: autosomal dominant, or produced by a defective gene contributed by one parent.
Myotonia congenita is caused by mutations in a gene
that carries instructions for a chloride channel,
a pore in
the
muscle cell surface that regulates the movement of
chloride molecules.
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Paramyotonia Congenita
Usual Age of Onset
Childhood to early adulthood
Disease Characteristics
Poor or difficult relaxation of muscles, which
may
worsen after exposure to cold or exercise.
Often associated with hyperkalemic periodic paralysis.
Condition causes discomfort but isn't life-threatening.
Inheritance
Autosomal dominant, or produced by a defective gene contributed by one parent.
Paramyotonia congenita occurs because there are
mutations in the gene that carries instructions for a
sodium channel,
a pore in the muscle cell surface that
regulates the movement of sodium molecules.
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Central Core Disease
Usual Age of Onset
Infancy to childhood
Disease Characteristics
Delayed motor development. Hip displacement is not
uncommon.
Condition can be stable to slowly progressive.
Inheritance
Autosomal dominant, or produced by a defective gene contributed by one parent; possibly autosomal recessive,
or produced by defective genes contributed by both
parents, in rare cases.
Central core disease has multiple origins; commonly
caused by defects in a gene that carries instructions
for a molecular "gate"
that releases calcium from inside
muscle cells.
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Nemaline Myopathy
Usual Age of Onset
Infancy to childhood
Disease Characteristics
Delayed motor development. Weakness of arm, leg,
trunk, face, and throat muscles. Respiratory
involvement
common.
Severity and progression vary.
Inheritance
Autosomal dominant, or produced by a defective gene contributed by one parent;
also autosomal recessive,
or produced by defective genes contributed by both parents.
Nemaline myopathy is caused by a variety of genetic
defects, each one affecting one of the filament
proteins
required for muscle tone and contraction.
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Myotubular Myopathy
Usual Age of Onset
Infancy
Disease Characteristics
Drooping of upper eyelids, facial weakness.
Weakness of the limbs and trunk muscles. Patients
almost always have no reflexes.
Respiratory involvement is possible.
Disease progresses slowly.
Inheritance
X-linked, or carried on the X chromosome and usually
affecting only boys;
autosomal dominant, or produced by a defective gene contributed by one parent; also autosomal recessive,
or produced by defective genes contributed by
both parents.
The most common form (X-linked)is caused by defects or deficiencies of myotubularin,
a protein thought to promote
normal muscle development.
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Periodic Paralysis
(Two Forms: Hypokalemic and Hyperkalemic )
Usual Age of Onset
Childhood to adulthood
Disease Characteristics
Episodes of generalized muscle weakness.
Hyperkalemic
type may be associated with paramyotonia
congenita.
Frequency of attacks and severity vary. May respond to
drug therapy.
Inheritance
In both forms, autosomal dominant, or produced by a
defective gene contributed by one parent.
Hyperkalemic is caused by high levels of potassium in the
blood interact in an unknown way with genetically caused
abnormalities in sodium channels (pores that allow the
passage of sodium molecules) in muscle cells.
Hypokalemic occurs because there are low levels of
potassium in the blood interact in an unknown way with
genetically caused abnormalities in calcium channels
(pores that allow the passage of calcium molecules) in
muscle cells;
sometimes also caused by genetic
abnormalities in channels for sodium or potassium.
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Neuromuscular Diseases included in MDA's Programs
Muscular
Dystrophies
Motor
Neuron Diseases
Inflammatory
Myopathies
Diseases
of Neuromuscular Junction
Diseases
of Peripheral Nerves
Metabolic
Diseases of Muscle
Myopathies
Due to Endocrine Abnormalities
Other
Myopathies
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