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Myotonic Dystrophies (DM)

Myotonic Dystrophies (DM)

These are autosomal dominant diseases, which are divided into two categories: Type I Myotonic Dystrophy (Steinert Disease - DM1) and Myotonic Dystrophy Type II (PROMM - DM2). While their symptoms are similar, they are distinguished by the different mutations causing them. DM1 is caused by mutations on the DMPK gene in which occur many repeats of a specific nucleotide sequence (CTG) of about 50 to 4000 times, while in DM2  the mutation occurs in Znf9 gene, where there is a distinguished repetition of the sequence (CCTG) 75-11.000 times.

 

DM1

It is divided into two categories: congenital and adult form. Type I congenital myotonic dystrophy presents symptoms from birth and is the most serious form. It has been found to be inherited to the offspring when the mother is sick, rather than the father. These newborns are very weak, with problems of feeding, swallowing, breathing. If they survive after infancy, they can overcome respiratory and feeding problems, but they present delays of milestones, that maybe impaired throughout time.

 

In adult DM1, symptoms occur between the ages of 10 and 40, showing great heterogeneity in their severity, progression rate and degree of disability. But generally, the disease develops slowly and has a frequency of 1: 8,000 births.

 

There is a possibility that the symptoms may occur later in childhood and this is different from the congenital form. In particular, speech problems and learning difficulties are present, but also cardiac arrhythmias or cardiomyopathy are present.

 

DM2

It occurs mainly in adulthood with marked symptoms from the age of 20 to 60 years. Its symptoms are similar to DM1 and in some cases milder and patients do not have the need for supportive devices.

 

Symptoms

Myotonia,

Muscular rigidity,

Muscular weakness and atrophy (in DM2 mainly in muscles near the torso),

Cramps and myalgia,

Bleached,

Tiredness and lack of resistance to physical activity,

Osteopenia and osteoporosis,

Delay in speech initiation or speech problems,

Dysplasia in lifting of the head,

Walking Disorder,

Difficulty when climbing up stairs or lifting from sitting upright,

Obstruction of grip or lifts of objects,

Gastrointestinal problems,

Cataract,

Heart rate disorders,

Swallowing problems,

Reproductive and respiratory problems,

Early hair loss,

Intense somnolence,

Tolerance to glucose and insulin, hypothyroidism / hyperthyroidism, hypercholesterolemia, hormonal problems,

Pain in the abdomen and muscles (depending on physical exercise).

 

Diagnosis

Clinical examination,

Genetic testing,

Electromyography,

Muscle biopsy.

 

Management

There is no cure, but significant efforts are being made to find it. However, individual symptoms are treated by various methods, such as:

 

Use supportive devices e.g. wheelchairs (DM1), splints,

Cataract monitoring and surgery,

Drug treatment of sleepiness, heart disorders, myotonia, insulin tolerance and pain,

Mechanical support of respiratory function,

Physical therapy,

Occupational therapy,

Speech therapy,

Psychotherapy,

Genetic counseling for subsequent pregnancies.

 

Information about clinical trials conducted globally: https://www.centerwatch.com/clinical-trials/listings/condition/350/muscu... and https://clinicaltrials.gov/ct2/home

 

References

 

Muscular Dystrophy Association