Muscular dystrophies belong to a group of genetic diseases characterized by loss of muscle mass and progressive weakness.

Both pathologies primarily affect skeletal and cardiac striated muscle tissue. These two forms of muscular dystrophy are predominantly found in males.

Epidemiology

The combined incidence of Duchenne and Becker muscular dystrophies is 1:3500-1:5000 male newborns worldwide.

Symptoms

Duchenne and Becker muscular dystrophies are the result of different mutations in the same gene and are characterized by almost similar symptoms.

These two pathologies differ in the severity of the course, age of onset of the disease, and degree of progression. Duchenne muscular dystrophy Clinical signs – Muscle weakness begins in early childhood and progresses rapidly. Affected children have difficulty with motor skills such as standing, sitting, and walking. By adolescence, such children become wheelchair-bound.

The symptoms and clinical course of Becker muscular dystrophy are milder. Muscle weakness develops in late childhood or adolescence and progresses slowly.

Duchenne and Becker muscular dystrophies involve damage to the heart muscle, called cardiomyopathy. This condition causes weakness of the heart muscle and a decrease in the efficiency of the heart's contractions. In both Duchenne and Becker muscular dystrophies, cardiomyopathy develops in adolescence, which is later followed by hypertrophy (enlargement) of the heart muscle, and ultimately dilated cardiomyopathy with heart failure. Dilated cardiomyopathy is characterized by arrhythmias, shortness of breath, extreme fatigue and weakness, and swelling of the extremities. In most cases, cardiac complaints progress rapidly and become life-threatening.

Life expectancy in men with Duchenne muscular dystrophy is on average 30 years, and with Becker muscular dystrophy – 40 years and sometimes more.

X-Constricted dilated cardiomyopathy is a condition that results from a mutation in the same gene. This condition is often called subclinical Becker's dystrophy. People with X-linked dilated cardiomyopathy do not develop symptoms of skeletal muscle damage, although subtle changes may be found in skeletal muscle cells.

 reason

Duchenne and Becker muscular dystrophies are the result of mutations in the DMD gene. The DMD gene is involved in the synthesis of the protein dystrophin, which is a structural protein in skeletal and cardiac striated muscles and provides cytoskeleton stabilization. It is also involved in the process of muscle contraction and relaxation.

Mutations in the DMD gene alter the structure and function of the dystrophin protein, sometimes leading to a complete blockage of its production. In the absence of dystrophin, active muscle activity leads to damage to its fibers, which ultimately manifests itself in skeletal muscle weakness and heart failure.

Diseases associated with abnormalities of the protein dystrophin are called dystrophinopathies. These are X-linked recessive diseases. Men have only one sex X chromosome, so even one damaged copy (allele) of the recessive gene is sufficient to develop the disease.

For the disease to develop in women, the mutated, recessive gene must be present on both sex X chromosomes, which is quite rare.

Due to the peculiarities of X-linked inheritance, dystrophinopathies are more common in men than in women.

A woman with only one sex X chromosome carrying the DMD gene mutation will not develop the disease, but she will be a carrier of the mutated gene. Very rarely, a woman with the mutation may develop mild muscle weakness or cramps (involuntary muscle contractions). There is also a relatively high risk of developing cardiomyopathy.

source

https://medlineplus.gov/genetics/condition/duchenne-and-becker-muscular-dystrophy/#causes

n.manjaparashvili@synevo.ge