Myotonic dystrophy (MTP, Steinert’s disease , dystrophic myotonia ) – AD, a multi-systemic disease characterized by variable gene expression (clinical polymorphism) in both sexes after the onset of the disease and the severity of the course. The genetics of MTD is well studied at the genealogical, formal genetic and molecular genetic levels. In patients from all countries, a mutation was detected in the muscle dystrophy protein kinase gene (symbol of the DM-PK gene) located on chromosome 19ql3.3. The essence of mutations – expansion (increase in number) of unstable CTG repeats in Z’- netranslovany portion of the gene (normal – 5 to about 30, and MMP 50-2500 above). A correlation between the severity and the number of trinucleotide repeats was revealed . The prevalence of MTD-1: 10000.
The main clinical manifestations: myotonia , muscle weakness, cataract (an early sign), cardiac arrhythmias, forehead baldness, impaired glucose tolerance, mental retardation, hypogonadism , amenorrhea, ovarian cysts, abdominal syndrome.
Muscle weakness is associated with the degeneration of swollen muscle cells and fiber atrophy. Myotonia and muscle weakness in patients are combined with impaired speech and swallowing. Muscular twitching and asymmetric weakness. First of all, the facial and temporal muscles are involved in the pathological process, then the cervical, brachial, and femoral muscles (from the proximal direction of the distal).
There are 4 forms according to the age “peak” of the onset of the disease: congenital, youthful, classical (20-30 years) and minimal (50-60 years). This is due to differences in the number of trinucleotide repeats at the MTP locus. Death occurs at the age of 50-60 years (in the classical form) as a result of complications. The clinical picture in homozygotes is expressed in a more severe form. In many families with MTP, anticipation is noted in several generations. Families with MTP are described in three or more generations: in the 1st generation, only cataracts, in the 2nd, moderate muscle weakness, and in the 3rd, a congenital form. In MTD, pronounced imprinting — the expansion of triplets occurs in women in meiosis, and this process is absent in spermatogenesis. Persons born to sick mothers have a more severe illness with an earlier onset than people born to sick parents.