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Centronuclear Myopathies-CNM

Centronuclear Myopathies-CNM

These are rare muscular diseases characterized by mild to severe muscle weakness. Often their symptoms are evident at birth, without excluding their appearance at any time. They are distinguished in autosomal and X-linked patterns of inheritance and are:

  1. Centronuclear myopathy associated with the BIN1 gene.
  2. Centronuclear myopathy associated with the DNM2 gene.
  3. Centronuclear myopathy associated with the RYR1 gene.

 

 

1. Centronuclear myopathy associated with the BIN1 gene.

It is a rare autosomal recessive form, with the mutations found in the homonymous BIN1 gene.

There is a wide variety of symptoms in limited recorded cases. There is progressive muscle weakness from birth or childhood to the extremities, eye-bleeding or facial blistering and difficulty in chewing. It may also develop into muscle atrophy. In addition, there may be breathing problems and feeding and development problems, particularly with regard to walking, which may stop until the age of 20. There are particular features in the face, which appear long and the palate has a large curvature, as well as other skeletal abnormalities, such as a large paw arch, articular folds, scoliosis, kyphosis.

 

All of the above symptoms are present in those who appear with the first symptoms at younger ages, while those starting at older ages have a milder clinical picture, mainly with muscle weakness of the limbs.

 

2. Centronuclear myopathy associated with the DNM2 gene.

It is an autosomal dominant form, with mutations in the homonymous gene, and symptoms are present from birth to adulthood with variation in severity.

They are often mild in nature, with growth being normal until adolescence, where fatigue, myalgia, leg cramps occur. Gradually, muscle weakness develops, usually starting from those points of the limbs near the torso. There may be difficulty in walking and running, which progresses in loss of walking ability until the 6th decade of life. Ophthalmoplegia, blistering may occur, and in children there may be additional difficulties in feeding, swallowing and breathing.

Cases of cataract, muscle hypertrophy, large tread arch, impaired jaw movement, scoliosis, and contractures of the Achilles tendon have been reported.

 

3. Centronuclear myopathy associated with the RYR1 gene.

It is an autosomal form either dominant or recessive and in infancy it is presented with intense hypotonia and weakness, which can gradually improve. Mainly the muscles of the torso and those close to it are affected, thus people present breathing, eating, walking and climbing problems.

The most serious cases have particular features in the face and may show scoliosis, lack of reflexes, ophthalmoplegia, bilateral ptosis of eyelids and muscle contractions.

 

This is a severe skeletal muscle weakness that affects mainly male individuals.

In neonates muscle weakness, muscle hypotonia, abnormal bone growth, muscle contractures and scoliosis develop, and finally it progresses to loss of walking, standing and sitting ability. In addition, ophthalmoplegia, weakness of the facial and respiratory muscles, which may require ventilator support, may occur, either during sleep or even continuously, in the absence of reflexes, large and narrow head, large palate curve, hepatopathy, otitis and respiratory infections and seizures .

 

 

Diagnosis

Clinical examination,

Genetic tests,

Muscle biopsy.

 

Management

There is no cure except for symptomatic treatment using supportive devices such as ventilators and feeding tubes. Systematic monitoring of patients by multidisciplinary medical team is required, and of course genetic counseling in the family for any future pregnancies.

 

For the Standards of Care you may visit the following article: https://drive.google.com/file/d/11iOxRi9jCtlNEXp9ihHhTKJJgZGUrIe8/view?u...

 

To monitor clinical trials on diseases visit: https://clinicaltrials.gov/ct2/home

 

References

Muscular Dystrophy Association