Introduction
Muscles are made up of fibers and around 600 different types of muscles present in the body. There are types of muscle tissue in the body, such as skeletal muscles (a part of the musculoskeletal muscle supports the weight of the body and movement), cardiac (this muscle lines the walls of the heart), and smooth muscle (these muscles lines the inside of the stomach and other organs). Myopathy is a muscle disorder; any sort of muscle disorder can lead to many physical difficulties, and one such condition is congenital myopathy.
What Is Congenital Myopathy?
A congenital (present at birth) myopathy (muscle disease) is a group of disorders that is present at birth or infancy. It is a rare inherited disorder that leads to a lack of muscle tone, and depending on the site and severity, congenital myopathy is divided into several types.
What Are the Different Types of Congenital Myopathy?
There are six types of congenital myopathy.
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Central Core Disease: Core myopathies are the most common type of congenital myopathy. It affects the skeletal muscles and can range from mild to severe.
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Mini core (Multicore) Disease: It is a rare inherited muscle condition and is another type of core myopathy.
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Nemaline Myopathy: It causes muscle weakness and reduced reflexes. It worsens the face, neck, pelvis, and shoulders.
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Centronuclear Myopathy: It affects an infant's eye movements.
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Myotubular Myopathy: It is a rare type of congenital myopathy that only affects male patients.
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Congenital Fiber-Type Disproportion Myopathy: It affects normal respiratory functions and can improve with age.
What Causes Congenital Myopathy?
Congenital myopathy is caused due to genetic mutation. The affected infant has problems with nerves that stimulate the child's brain and muscles. Different types of congenital myopathies are caused due to different types of gene mutations, such as:
RYR1 Gene: Ryanodine receptor 1 or RYR1 gene provides instruction to make the ryanodine receptor 1 protein. The RYR1 is present in the membrane that surrounds a muscle cell structure (sarcoplasmic reticulum). When turned on or activated, these proteins release positively charged calcium ions. The calcium ions are stored in the structure when the muscles are at rest. When the calcium ions are released from the sarcoplasmic reticulum into the cell fluid. The released calcium ions help the muscles to move. In central core diseases and congenital fiber-type disproportion type of congenital myopathy, the amino acids of a certain area of RYR1 protein are affected. The mutated gene disrupts the normal structure of the RYR1 channel and alters the calcium ion flow within the muscle cells. This leads to muscle weakness.
DNM2 Gene: The DNM2 gene gives instructions for making dynamin 2 protein. These protein cells are all over the body. The protein interacts with the cytoskeleton, such as an actin tube-like structure called microtubules. Centronuclear myopathy is caused due to 25 mutations in the DNM2 gene. The single DNA (deoxyribonucleic acid) building acids are changed due to mutation in a gene region such as exon 8 and exon 11. These mutations change the DNM2 structure, which causes centronuclear myopathy.
What Are the Symptoms of Congenital Myopathy?
Depending on the type, the symptoms can vary for congenital myopathy. Some of the common symptoms include:
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Muscle weakness in the child’s shoulder, neck, pelvis, and head.
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Due to muscle weakness, an individual is not able to breathe normally or has difficulty in breathing.
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Flopiness or hypotonia is one of the most common symptoms in which there is a loss of muscle tone.
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Normal functions like sucking from a bottle, eating from a spoon, and chewing become very difficult.
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Developmental delays such as turning over and sitting up.
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Difficulty in walking due to muscle weakness.
What Are the Different Modalities Through Which Congenital Myopathy Can Be Diagnosed?
A pediatrician will examine the child clinically and ask the parents about the symptoms seen recently. To confirm the diagnosis, certain tests are advised, such as:
Genetic Testing - It examines the DNA, which is a database that carries instructions for the body’s functions. It is always informed before genetic testing that, in some cases, the negative result does not confirm the diagnosis, and the test can be performed again. The blood test is done by a healthcare expert who takes the blood from the arm’s vein, and the sample is sent to the laboratory for further testing.
Blood Test - Another blood test can be done for an increased muscle enzyme level (creatine kinase).
Electromyogram (EMG) - EMG is a diagnostic test that measures the nerves and muscles work. A healthcare expert will ask the patient to remove any jewelry or hairpins. The neurologist will locate the muscle, and a sterile needle will be inserted. A ground electrode will be placed under the leg or arm. The test can be slightly painful, and the electrical activity of the muscle will be measured on an oscilloscope.
Muscle Biopsy - Any cell changes in a child’s muscles can be easily detected through a muscle biopsy.
How Is Congenital Myopathy Treated?
Treatment options include:
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Genetic counseling can be given to the patient’s family to make them understand the severity of the condition and also helps to make the family planning decision.
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Avoid an unhealthy diet, and adequate exercise helps make muscles healthy.
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Physical therapy is done to help regain muscle strength.
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Speech therapy helps children who have difficulty speaking.
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Albuterol is an experimental drug used to relieve muscle weakness in children.
Conclusion
Congenital myopathy is a rare inherited condition that is caused due to genetic disorders. Genetic mutation of certain genes can lead to a different type of congenital myopathy. An affected individual has weak muscles and delayed motor skills. The symptoms are easily visible early and can be diagnosed using different modalities. The child can live a normal life if a healthy diet and different therapies like speech and physical therapy are given regularly.
