Steinert’s myotonic dystrophy: when muscles become unresponsive

Today is International Myotonic Dystrophy Day, a rare disease with no treatment or cure to date. Although Myotonic Dystrophy is not within the Oligofastx project, it is one of the diseases on which Arthex Biotech (Oligofastx partner company) is researching and working to find a therapeutic solution. Specifically, Arthex is developing an experimental RNA-based drug for the treatment of this disease, ATX-01, which will enter the clinical phase in 2023.

Myotonic Dystrophy is a disorder that can result from genetic inheritance with a spontaneous flare. This disease affects 1 in 8000 people regardless of whether they are male or female.

The age of onset is highly variable, ranging from prenatal to adulthood. The clinical manifestations also cover a wide range and may differ between relatives and between affected families.

Five forms are currently recognized: congenital, early childhood, juvenile, adult-onset and late-onset. Congenital disease (15% of cases) is the most severe form and includes severe generalized weakness at birth with respiratory distress, hypotonia and feeding problems. Subsequently, patients develop cognitive and motor retardation, intellectual disability and autism spectrum disorders.

The course can be fatal in the congenital form (30-40%). In childhood-onset cases (1-10 years of age), the main clinical manifestations involve muscle weakness (including both proximal and distal muscle groups, facial weakness, respiratory and gastrointestinal complications such as respiratory distress, aspiration, dysphagia, constipation and speech disorders), myotonia, respiratory sleep disorders, recurrent infections, cognitive impairment, psychiatric disorders (phobia, depression, anxiety, attention deficit hyperactivity disorder).

The juvenile form, with onset between 11 and 20 years of age, is characterized by school and behavioral problems and is often unrecognized. The classic adult form (75% of cases), which develops between 20 and 40 years of age, is characterized by progressive weakness of the distal musculature, pain, myotonia and multiorgan involvement (irritable bowel syndrome, conduction and other cardiac disorders, cataracts, ophthalmoplegia, diabetes mellitus, hypogonadism, hypoandrogenism and thyroid dysfunction).

Intellectual deficit is also present in adult patients. Alopecia may be present in both males and females and infertility may also be present. Late-onset disease after the age of 40 years includes mild myotonia and weakness, daytime sleepiness and cataracts. An increased risk of cancer has also been described in affected patients.


Symptoms progressively advance, reducing life expectancy

This disorder causes muscle weakness and atrophy to varying degrees, affecting the limbs, mainly the hands, and even the facial muscles.

In most cases, the reasons for first consultation are caused by sleep disorders. Daytime hypersomnia affects one third of patients, accompanied by periodic movements during sleep. Apnea or hypopnea are also quite frequent in these cases.

As the disease progresses, difficulties in the cardiac muscles (cardiomyopathy) may occur, altering the heart rhythm. Patients with extreme muscular atrophy present many other symptoms, such as drooping eyelids, cataracts, early baldness (in males), arrhythmias or diabetes, among others. Because of all these complications, the life expectancy of patients does not exceed 55 years.