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    Muscle Related Disorders


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.