Muscular dystrophies are a set of genetic disorders which affects the muscular strength and cause muscle degradation over the time. They are characterized by progressive muscular weakness be observed on microscopic level. The disease Duchenne muscular dystrophy (DMD) falls under the muscular dystrophies which was first described by the French neurologist Guillaume Benjamin Amand Duchenne in the 1860s.
The Gene
It is an X-linked disease recessive disorder that affects 1 in 3600–6000 live male resulting due to mutations (mainly deletions) in the gene (DMD; locus Xp21.2).The mutated gene encodes for the protein dystrophin.
The Protein Dystrophin
Dystrophin is a normal residential component in skeletal, cardiac and smooth muscles with much lower amounts in the brain and peripheral nerves. In the muscles and neurons, dystrophin is found at the myotendinous junction and at the postsynaptic membrane of the neuromuscular junctions and binds to muscle fibers called actin and interacts with a dystrophin–glycoprotein complex (DGC) which bridges the cytoskeleton, the basal lamina and the plasma membrane.
In DMD, dystrophin is absent from skeletal and cardiac muscles as revealed by immunocytochemical and immunological analysis of skeletal muscle biopsy.
In DMD, there is a progressive proximal muscle weakness which usually becomes noticeable during early childhood. The first sign of muscle weakness in a boy begins as early as age 3. With the time the muscle strength diminishes child becomes wheelchair bound till he reaches 12 years of age approximately.
Death usually occurs due to complications like chronic respiratory insufficiency and/or cardiac failure. Although the disorder targets skeletal muscles predominantly, progressive cardiomyopathy is commonly seen in the patients of DMD which can be severe.
Milder allelic forms of the disease include intermediate muscular dystrophy and Becker muscular dystrophy, which cause loss of ambulation at 13–16 years or over 16 years, respectively.
The DMD affected individuals might have mildly delayed motor milestones and most are unable to run and jump properly due to proximal muscle weakness. A classic way of rising from the floor called the Gowers’ manoeuvre can be seen in such cases. Most patients are usually diagnosed at approximately 5 years of age, as their physical ability reduces remarkably from that of their peers.
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Symptoms of DMD
- Muscle weakness – The first muscles which get affected are those around the hips and upper thighs. Children may have difficulty walking, running, jumping, climbing stairs or standing up from the floor.
- Loss of muscle coordination – making children unsteady, clumsy, to fall often or “waddle” when they walk.
- Muscle size – As the muscles get damaged, they are replaced by fat and connective tissue and shrink (muscular atrophy) and the calf muscles often become larger (hypertrophy)
- Toe walking – The muscles become tight around joints, limiting movement. When walking becomes difficult, children may walk on their “tippy-toes”.
- Learning disabilities.
- Muscles of the heart and those around the lungs are affected later in the disease
Diagnosis
Blood tests
- Creatinine phosphokinase levels – Weak and damaged muscles release an enzyme called creatinine phosphokinase into the blood. On estimation, high levels of CK in children reveal DMD or another muscle disease.
- Genetic tests – Estimation of abnormal gene for DMD in the blood sample.
Muscle biopsy
- A muscle biopsy is only needed when the first genetic test is negative which occurs in about one-third (30%) of cases.
TREATMENT
The basic aim of the treatment revolves around controlling the symptoms, and to keep muscles working as long as possible to give the affected child the best possible quality of life as there is no cure for DMD.
Treatment options can be
Physiotherapy: A daily program of suitable stretching exercises to keep muscles and joints moving for as long as possible. Swimming and exercising in water can be helpful as these activities do not put a lot of stress on joints.
Corticosteroids: They can help slow the progress of the disorder although they may have side effects.
Assistive devices: Orthotics, braces, canes and walkers can help the child to walk and do things for himself. A wheelchair can help the child to get around.
Orthopedic treatment: As the disorder progresses, tendons and joints become tight and the bones in the back and chest can become deformed, this may require treatment and possible surgery.
Treatments to help with breathing: Muscle weakness and changes in bones contribute to problems with breathing. BiPAP and other machines can help make breathing easier in the later stages of the disorder.
Treatments to help the heart: As DMD can lead to high blood pressure and heart problems like cardiomyopathy, medications to lower blood pressure may be needed.
As a parent it is easy to be overwhelmed by your child’s diagnosis with diseases of this magnitude but it is important to know that you can cope with the emotional and physical tasks that lie ahead, if you take small steps, prioritize and listen to the needs of your family.
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