Abstract
The myotonic dystrophies (DM) are primary, progressive and degenerative disorders of skeletal muscles. Besides involvement of skeletal muscles, they cause heart, eyes, endocrine and brain disorders.
DM are the most common muscular dystrophies in adults, they cause life shortening and affect quality of life. Main clinical features are myotonia and progressive muscle weakness.The classification distinguishes two main types of DM -myotonic dystrophy type 1 (Steinert's disease), myotonic dystrophy type 2 (proximal myotonic myopathy, PROMM).
A special type of DM1 is congenital myotonic dystrophy. The molecular genetics procedures are the most important diagnostic tools to establish the correct diagnosis.
The molecular basis of myotonic dystrophies is expansion of an unstable trinucleotide repeat sequence CTG in noncoding part of a DMPK1 gene in DM1 and tetranucleotide repeat sequence CCTG of ZNF9 gene in DM2. Further, electromyography is an important diagnostic procedure to confirm specific myotonic discharges in skeletal muscles.
The causative treatment is not available, but long term cardiological and ophtalmological care is required. The genetic counseling is very important in DM1 and DM2 families.