MYOTONIA CONGENITA - Everything You Need To Know
Medikoe Health Expert
Koramangala, bengaluru, karnataka, india, Bengaluru Feb 9, 2017
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:
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
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
Potassium channel disorders
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-
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.
Are you looking for a health expert around you?
Medikoe is an online platform that allows you to search and connect with the most qualified and experienced doctors near you. Have a query related to health? Get it answered for free within 24 hours only at Medikoe. Download Medikoe's Mobile app and book an appointment with a doctor for free.