|
Myotonic Dystrophy (DM)
Myotonic
Dystrophy is a chronic, slowly progressing, highly variable multisystemic
autosomal dominant disease in which the muscles contract but have decreasing
power to relax. Myotonic dystrophy can cause mental deficiency, hair loss and
cataracts. Two types of adult onset myotonic dystrophy exist. Type 1 (DM1;
MIM: 160900),
also called Steinert's disease, has a severe congenital form and a milder
childhood-onset form.
In DM1,
there is a repeat-expansion of the triplet (CTG) in the DMPK gene,
which codes for myotonic dystrophy protein kinase.
Also called proximal myotonic myopathy (PROMM), myotonic dystrophy type 2 (DM2;
MIM: 602668)
is due to a different mechanism than DM1 and generally manifests with milder
signs and symptoms. Here, the specific defect is a repeat expansion of the
tetranucleotide CTG in the ZNF9 gene
leading to an
altered messenger RNA.
Considering the studies done in India to date, this database presently holds the relevant data for Myotonic Dystrophy Type 1 only.
Duchenne Muscular Dystrophy (
MIM: 310200)
The
features of Duchenne muscular dystrophy are progressive proximal muscular
dystrophy with characteristic pseudohypertrophy of the calves, the myocardium
is affected, massive elevation of creatine kinase levels in the blood,
myopathic changes by electromyography, and myofiber degeneration with fibrosis
and fatty infiltration on muscle biopsy. Duchenne muscular dystrophy is caused
in an X-Linked recessive mode by mutation (deletions of one or many exons) in
the gene encoding dystrophin (DMD). It affects one in 3500 males.
Becker Muscular Dystrophy (
MIM: 300376)
Becker's
Muscular Dystrophy is related
to Duchenne muscular dystrophy but is less severe I nature; also
an X-linked recessive inherited disorder characterized by slowly
progressive muscle weakness of the legs and pelvis caused by insufficient
dystrophin produced in the muscle cells, resulting in instability in the
structure of muscle cell membrane. Like Duchenne muscular dystrophy, it is also
caused by mutations in the dystrophin gene, but in DMD no
functional dystrophin is produced thus, making DMD much more severe than BMD.
Myotubular Myopathy (
MIM: 310400 )
Myotubular
Myopathy is a family of rare, idiseases manifesting itself as a defect in the
cell structure of voluntary muscles causing low muscle tone and, in most forms,
is usually apparent at birth. Affected children have diminished respiratory
capacity and are often partially or totally ventilator dependent. There are
three types of myotubular myopathy based on the pattern of inheritance and
clinical severity -- X-linked, autosomal dominant and autosomal recessive.
Presently, the database harbours information for X-linked recessive myotubular
myopathy, the most severe form, caused by defects in the MTM1 gene and is
generally presented at birth in affected males.
Hypertrophic cardiomyopathy I (
MIM: 192600 )
Hypertrophic cardiomyopathy-1
is caused by mutation in the MYH7 gene with autosomal dominant pattern of
inheritance. In early stages the disease is characterized by a presystolic
gallop due to an atrial heart sound, and EKG changes of ventricular
hypertrophy. In later stages due to progressive ventricular outflow obstruction
it may lead to palpitation associated with arrhythmia, congestive heart
failure, and sudden death.
Hereditary Inclusion Body Myopathy 2 (
MIM: 600737 )
Hereditary
Inclusion Body Myopathy 2 primarily affects skeletal muscles and is
caused
by mutations in GNE gene (
MIM: 603824).
This disorder causes
muscle weakness that appears in late adolescence or early adulthood. As the
disorder progresses, muscle weakness and wasting affects the muscles of the
upper and lower limbs. This condition is inherited in an autosomal recessive
pattern.
|