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MYOTONIA CONGENITA - Everything You Need To Know

Medikoe Health Expert

Medikoe Health Expert

  Koramangala, bengaluru, karnataka, india, Bengaluru     Feb 9, 2017

   6 min     



Myotonia congenita, also known as Thomsen and Becker disease, or Myotonic Muscular Dystrophy is an inherited congenital condition prevalent in the northern region of Scandinavia. It is a genetic disorder which affects muscle contraction or relaxation.

Characterized by the inability of the skeletal muscles to relax quickly after voluntary movements, the hallmark of the disease is the failure of initiated decrease to terminate, often referred to as delayed relaxation of the muscles (myotonia) and rigidity.

The infant form of Myotonic Muscular Dystrophy is more severe than the adult form. It occurs in babies born to parents who have the adult form, even if the parents have very mild cases.

MMD is sometimes also referred to as fainting goat syndrome, as it is responsible for the eponymous 'fainting' seen in fainting goats when presented with a sudden stimulus. However, it is quite rare and is estimated to affect 1 in 1,000,000 people worldwide. 

Causes of Myotonia Congenita

Mutation or genetic change is the leading cause of myotonia congenital. It is caused by mutations in the gene for a chloride channel that's necessary for shutting off the electrical excitation that causes muscle contraction and is characterized by the inability of the skeletal muscles to relax after voluntary movements quickly.

The genes are inherited from either one or both parents to their children. The Becker type is generally inherited in an autosomal recessive pattern, which means that it is produced by defective genes contributed by both the parents. On the other hand, Thomsen myotonia is autosomal dominant, which means that it is produced by a defective gene contributed by one parent.  

Types of Myotonia Congenita

Two types of Myotonia Congenita exist. One is Autosomal dominant form and the other one is Autosomal recessive form. These two types of myotonia congenita are also known as Becker disease, which is the most common, severe and generalized form; and Thomsen disease, which ia a milder and rare form. Both of these forms are caused by various mutations in the CLCN1 gene. The Becker type inherits in an autosomal recessive manner, and the Thomsen type inherits in an autosomal dominant manner.

1. Becker Disease

Becker muscular dystrophy (BMD) is an inherited medical condition that causes progressive weakness and wasting of the skeletal and cardiac muscles. It primarily affects males. The age of onset and rate of progression can vary from person to person. 

Muscle weakness usually becomes apparent and can be noticed between the ages of 5 and 15. In some cases, heart involvement (cardiomyopathy) can also be the first sign. Becker disease is caused by a mutation in the DMD gene and is inherited in an X-linked recessive manner. 

2. Thomsen Disease

Thomsen Disease genetic disease of skeletal muscle membrane hyperexcitability caused by variants in CLCN1, leading to reduced conductance of the main skeletal muscle chloride channel. This disorder is inherited in an autosomal dominant, sometimes associated with reduced penetrance. Thomsen disease is rare and exhibits a high degree of genetic heterogeneity. 

Symptoms of Myotonia Congenita

Symptoms of MMD typically begin in childhood and vary from person to person. They may include muscle stiffness, muscle weakness, or attacks of weakness brought on by movement after rest. Some patients with myotonia congenita are prone to falling as a result of quick or hasty movements or an inability to stabilize themselves after losing balance.

The two major types of myotonia congenita, Thomsen and Becker are distinguished by the severity of their symptoms and their patterns of inheritance. As more and more of the individual mutations that cause myotonia congenita are identified, the limited disease classifications are becoming less widely used. 

The major symptoms of the disease may include:

  • Frequent falls

  • Gagging/refluxes

  • Gagging

  • Stiff movements

  • Difficulty in swallowing

  • Shortness of breath

  • Tightening of the chest and muscles at the beginning of an exercise

  • Difficulty in opening eyes after forcing them closed or crying

  • Attacks of weakness and giddiness brought on by movement after rest.

Possible Complications of Myotonia Congenita 

  • Swallowing difficulties causing tremendous weight-loss

  • Chronic joint problems

  • The weakness of the abdominal muscles

  • Aspiration pneumonia

  • Gagging, Frequent choking, or trouble swallowing in an infant 

Diagnosis of Myotonia Congenita 

Making a diagnosis for a rare or genetic disease can often be challenging. Doctors generally rely on signs and characteristics and symptoms to distinguish the two forms of Myotonic Muscular Dystrophy. However, myotonia caused by CLCN1 mutations can sometimes be indistinguishable clinically from myotonia caused by sodium channel mutations. 

The health care provider or doctor may ask if there is a family history of myotonia congenita. Tests for the disease may include:

  • Genetic testing Registry

  • Sodium channel myotonias

  • Dystrophies

  • Potassium channel disorders 

  • Muscle biopsy

  • Electromyography (EMG, is a test of the electrical activity of the muscles) 

Treatment of Myotonia Congenita

In some cases of myotonia congenita treatment is not required, or it is determined that the risks of the medication outweigh the benefits. Treatment for the disease may include medication for muscle stiffness, such as carbamazepine, mexiletine, or phenytoin. Other treatments for the disease may include-

  • Phenytoin

  • Tocainide

  • Procainamide

  • Carbamazepine

  • Quinine (rarely used now because of side effects)

Exercise may temporarily alleviate myotonia. Some people with myotonia congenita have even reported more long-term relief with gymnastics. Physical therapy and other rehabilitative measures in case of MMD may also be used to help muscle function. Genetic counselling is available.

People with this disease may be at increased risk for harmful side effects of anaesthesia. Therefore, it is highly recommended that relatives of a person with the disease must be tested during childhood.

Does Myotonia Congenita run in the Family?

Myotonic Muscular Dystrophy is certainly a disease that runs in families. Both the types- Thomsen and Becker are inherited in an autosomal dominant pattern, which means it takes only one flawed gene to cause the symptoms of the disease. So, even if one parent has the disorder, every child of that person has a 50 per cent chance of inheriting the gene that causes it. 

However, Myotonia congenita (MMD) has its onset in early to late childhood and does not progress later on. Someone with myotonia congenita can lead a long, productive life, and can even excel at sports where strength is more important than agility.

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Tags:  well being,MYOTONIA CONGENITA

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i Pog
i Pog |  November 26th, 2020

this article is full of inaccuracies. myotonia congenita is the disease of the chloride channel in muscles. there are two types of it: becker's myotonia and thomsen's myotonia (they're almost identical, the main difference is the pattern of their inheritance: becker is autosomal recessive, thomsen is autosomal dominant). there's another group of myotonias, called potassium-aggravated myotonias (they all inherited in an autosomal dominant pattern). they are sodium channel diseases, where the symptoms are very similar to myotonia congenita (just caused by a different gene mutation). there is also a disease called becker's muscular dystrophy, but it's not myotonia. so the problem with this article is: it merges becker's myotonia (which is a muscular disease without dystrophia, and it inherits in autosomal recessive pattern) with becker's muscular dystrophy (which is not myotonia, and not exclusively connected to becker's myotonia, as it is a different gene mutation, and inherited in an x-linked domimant pattern).