This disease is inherited in an autosomal dominant fashion.
Trinucleotide repeat inheritance results in the accumulation of CTG repeats, and worsening of the disease over generations.
CTG is the trinucleotide repeat sequence. It is found on the DMPK gene, on the long arm of chromosome 19.
Atrophy of the muscles of the face is characteristic of myotonic dystrophy, often leading to ptosis and a typical facial appearance.
Frontal balding is an additional finding in many of these patients.
Sustained grip is one of the classic findings in myotonic dystrophy, and is caused by conduction defects and subsequent inability to inhibit the increased tone of grip.
Conduction defects can be found in patients with the disease due to nerve damage.
Cataracts are the clouding of the lens in the eye that obstruct the passage of light. They are present in almost every patient and may be detected early in the course by slit-lamp examination.
Histochemical stains have demonstrated selective atrophy of type 1 fibers in patients. Type 1 fibers are slow-twitch and oxidative fibers that contain large amounts of myoglobin and mitochondria with many blood capillaries, giving the muscle a red appearance.
Testicular atrophy is a characteristic finding in myotonic dystrophy.
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