Myotonic Dystrophy Type I


Myotonic dystrophy type 1 (DM1), also known as Steinert’s disease, is the most common neuromuscular disease in adults (around 1/8000). It is an autosomal, dominant disorder caused by the expansion of a (CTG)n triplet repeat in the DMPK gene, located on chromosome 19.

The disease is characterized by a wide clinical spectrum and underlying molecular mechanisms, making it one of the most complex genetic disorders.


Symptoms include muscle weakness, myotonia, multiple endocrine disorders, respiratory insufficiency, heart issues (conduction, arrythmia…), eyes problems, gastrointestinal tract, and brain. Cognitive dysfunctions combine their effects to other symptoms and make difficult family and professional life. The disease affects preferentially distal muscles.

The variability of symptoms is very high from one patient to the other, even in the same family, from a simple late onset cataract up to a congenital form engaging prognostic early in the life.

Anticipation. The disease is submitted to amplification from one generation to the following, with, usually, increased symptoms severity.


Research is very active worldwide, with several highly promising molecules in development. Antisense Oligo-nucleotides or gene-editing technique (CRISPR) have demonstrated potential efficiency in fighting the genetic abnormality itself, but, at the time, only symptomatic treatments are available.

Most of the countries have developed registers to characterize the disease and facilitate research. The most advanced registry features more than 3800 patients in France.


Diagnostic is usually made by neurologists through Electromyography techniques or using a blood test counting the CTG repeats. Sometimes, early age cataracts or myotonia particular pattern may result in indirect diagnostic. The birth of a child affected by the congenital form is also a sudden reveal situation.