Myotonic dystrophy

Myotonic dystrophy (DM) is a chronic, slowly progressing, highly variable inherited disease that can manifest at any age from birth to old age. It is characterized by a wasting of the muscles (muscular dystrophy), opacity of the lens of the eyes (cataracts), heart conduction defects and myotonia (difficulty relaxing a muscle). Most notably, the highly variable age of onset is not randomly distributed within a family, but shows a highly characteristic decrease in successive generations, a phenomenon termed anticipation.

Related Topics:
Chronic - Disease - Cataracts - Myotonia - Anticipation

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DM is a genetic disease which is inherited in an autosomal dominant way, meaning that inheriting a mutant gene from one parent will result in the disease- similar to Huntington's Disease, there is a 50% chance of inheriting DM from an affected relative. The affected gene is called DMPK (Myotonic Dystrophy Protein Kinase) which codes for a myosin kinase expressed in skeletal muscle. The gene is located on the long arm of chromosome 19.

Related Topics:
Genetic disease - Autosomal dominant - Huntington's Disease - DMPK - Chromosome 19

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DM is one of several known trinucleotide repeat disorders. Certain areas of DNA have repeated sequences of two or three nucleotides. There is a triplet repeat of Cytosine - Thymine - Guanine (CTG) in the DMPK gene. The number of repeats varies greatly from person to person, but the average number in a healthy person is between 5 and 37. Sometimes when repetitive sequences of DNA are replicated during cell division the cellular machinary slips and an extra copy of the triplet repeat is added to the sequence. Once there are more than 37 triplet repeats in the DMPK gene the sequence becomes unstable and slippage becomes a lot more likely to happen.

Related Topics:
Trinucleotide repeat disorders - DNA - Nucleotides - Cytosine - Thymine - Guanine - Cell division

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People affected with DM have over 50 and can have as many as 2000 repeats. As individuals with DM age and their cells replicate more and more the expanded triplet repeat becomes larger and larger due to its instability. The result of this is that the repeat size of an individual with DM will become larger the older they are. This explains the phenomenon of anticipation, as each child of an affected adult will have a larger expansion than their parent due to slipage during gametogenesis.

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Individuals with larger expansion have an earlier onset of the disorder and a more severe phenotype.

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The EMG has the typical sound of the dive bombers from WWII, called "Sturzkampfbomber-Geräusch"

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Also called dystrophia myotonica, myotonia atrophica, Steinert's disease.

Related Topics:
Myotonia atrophica - Steinert's disease

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