Myotonic dystrophy

Myotonic dystrophy is a group of inherited disorders that cause delayed muscle relaxation, progressive weakness, and effects across multiple body systems. Its main forms, types 1 and 2, arise from expanding DNA repeats.

CTG repeat expansion: An increase in repeated CTG DNA sequences in the DMPK gene, associated with myotonic dystrophy type 1. This expansion drives type 1 and can grow across generations.
Myotonic dystrophy type 1: A form of myotonic dystrophy caused by a CTG repeat expansion in the DMPK gene. It is the best-known form and can affect muscles, heart, eyes, and other systems.
Electromyography: A test that records the electrical activity of skeletal muscles using electrodes. It can detect characteristic myotonic discharges in affected muscles.
Myasthenia gravis: An autoimmune disorder in which impaired neuromuscular transmission causes fluctuating muscle weakness. Weakness may resemble myotonic dystrophy, but delayed relaxation and repeat expansions point elsewhere.
CCTG repeat expansion: An increase in repeated CCTG DNA sequences in the CNBP gene, associated with myotonic dystrophy type 2. This expansion is the genetic cause of type 2.
Myotonic dystrophy type 2: A form of myotonic dystrophy caused by a CCTG repeat expansion in the CNBP gene. It often features proximal muscle pain and weakness rather than severe distal weakness.
Genetic testing: Laboratory analysis of DNA to identify genetic variants or repeat expansions associated with disease. It can confirm the diagnosis and distinguish type 1 from type 2.
Congenital myopathy: A group of genetic muscle disorders usually presenting with weakness from birth or childhood. It can cause inherited weakness without the characteristic myotonia of this disorder.
RNA toxicity: Cellular dysfunction caused by RNA molecules that bind or sequester proteins needed for normal gene regulation. Expanded repeat RNA disrupts protein activity and splicing in affected tissues.
Myotonia: Delayed relaxation of a muscle after voluntary contraction or electrical stimulation. It gives the disorder its name and is a defining clinical feature.

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