Duchenne Muscular Dystrophy and Its Pathophysiology

Introduction

Duchenne muscular dystrophy is categorized as a muscular dystrophy of the severe type. In this case, the condition results in muscle degeneration progression. Ultimately, a patient suffering to DMD might be afflicted with ambulation loss, leading to death. It is important to note that one in every 3500 males usually fall victim to this affliction (Anderson and Bushby 111). As such, DMD is ranked amongst the types of muscular dystrophies that are quite prevalent. By and large, the affliction is only evident in males, but at the same time, their female counterparts may as well act as carriers. However, in case the father of a female happens to be afflicted and at the same time, the mother acts as a carrier, the female in question could then be afflicted. When the dystrophin gene undergoes mutation, this normally causes the occurrence of the disorder. The dystrophin gene in question acts as a code for the dystrophin protein. This particular protein plays a significant role within the muscle tissue structural component. The appearance of symptoms to this condition begins as early as at 5 years amongst male children, although they might as well develop these even at infancy. Although there are many symptoms associated with Duchenne Muscular Dystrophy, nonetheless, the first one to be observed is that the proximal muscles of the victims’ legs starts to show signs of weakness. Next, the proximal muscles of the pelvis also weaken. It is important to note that the weakening process of these muscles mentioned occur in a progressive manner.

Ultimately, we have the spreading of this weakness to other parts of the body such as the neck and arms. Low endurance, pseudohypertrophy and difficulty in staircases ascension are some of the most common early signs of the disorder. With time, a patient experiences wasting of muscle tissue, ultimately leading to fibrosis.

Main body

Anderson and Bushby (111) asserts that muscular dystrophy falls in the category of x-linked congenital disorders which result in children having progressive loss of muscle tenacity. Approximately one in about 3,500 to 5000 males born is likely to suffer the disorder at some time in his live. Although there are various types of muscular dystrophy, however, the most common among these is Duchenne Muscular Dystrophy. This from also includes FORM Becker Muscular Dystrophy in its mildest state.

Due to its association with the x-chromosome, muscular dystrophy most commonly affects males who inherit the mutation from their mother. However, about a third of Duchenne muscular dystrophy cases did not inherit the mutant gene from their mother; but developed it a new.

According to Wu (792), Duchene Muscular Dystrophy is a degenerative neuromuscular condition which is characterized by deficiency in dystrophin muscle protein. The genetic basis for this disease is a mutation in the dystrophin gene found in the x-chromosome. Dystrophy tends to occur more in both skeletal and cardiac muscles, as opposed to the smooth muscle. This disease therefore causes muscle to degenerate progressively leading to muscular weakness.

Usually, boys suffering from Duchene muscular dystrophy have central nervous system dysfunction coupled to the muscular disorder. These central nervous system disorders include learning disabilities and psychological retardation. According to a survey cited by Wu that involved 80 patients with this muscle disease, they depicted deterioration in their verbal abilities in relevance to their siblings. Nevertheless, an association of this myopathy with autism spectrum disorder has been discovered recently once as an only case report (Wu 792).

Symptoms of Duchenne muscular dystrophy

They normally begin to manifest when the boy child is between 3 to 6 years of age, through signs which include:

  • Frequent falls by the child.
  • Difficulty in standing.
  • Belated walking stage in child growth process.
  • Pseudohypertrophy of the calf muscle.
  • Walking on toes
  • Easy tiredness after or during a habitual physical activity.

Pathophysiology Of Duchenne Muscular Dystrophy

For the past 15 years, comprehensive knowledge of the connection between dystrophin deficiency and progressive muscular degeneration has eluded research scientist. However, the responsible gene mutation and its dystrophin products have been characterized. To begin with, dystrophin plays a major structural role in muscle fibre, which involves the stabilization of the plasma membrane, although other possible function may involve signalling. Thus, unusual muscular contractions results in high stress on the fragile plasma membrane and subsequent micro-lesions leading to loss of calcium homeostasis and eventual necrosis. Progressive probable events of this disorder which include inflammation, altered regeneration, fibrosis, and impaired vascularisation, vary among individuals thereby highlighting the significance of epigenic factors in the disorder (Deconinck and Dan 6).

Causes/risk factors

The basis for Duchenne muscular dystrophy is the x-linked dystrophin gene mutation and it often has no family history connection. The probability of its occurrence is highest in boys than in girls because of its nature of inheritance. The sons of the mutant carrier mothers have a 50% probability of developing the symptoms of the disorder while daughters have 50% chance of carrying the mutant gene. Thus, the main risk factor of developing this disease includes a family history of Duchenne muscular dystrophy as illustrated in the figures below.

Causes/risk factors

Causes/risk factors
Figure 1: source; A.D.A.M, 2010.
Causes/risk factors
Source; A.D.A.M, 2010.

According to the first figure, a male offspring who receives a single x chromosome from a carrier mother will develop the disorder. The second figure illustrates how daughters may inherit the disorder from her carrier mother or from her defective father. In both cases the daughter will be a carrier and will transmit the mutant to her offspring. However, the severity of her condition will be minimal relative to the boy’s. Based on the provided illustration, for a daughter born to a carrier mother and a normal father, there is a 25 % chance that such a daughter will be born normal.

Diagnosis

The methods for testing this condition include electromyography (EMG), genetic testing, muscle biopsy and serum CPK. EMG involves checking on the health conditions of the muscle and its motor nerves by using a needle electrode. This enables the electrical activity of the muscles to be visualized, whilst testing a nerve conduction speed (Nenshi and Strode 4). The muscle biopsy involves the structural and biochemical examination of a tiny piece of the muscle to ascertain the presence of dystrophin. In contrast, the CPK test entails creatine phosphokinase enzyme measurement. This particular enzyme resides in skeletal, heart and brain muscles.This test reveals the extent of degeneration of the muscle. The DNA test helps to ascertain the presence of the mutant gene and thus affirms any suspicion of the disorder.

Treatment

The cure for Duchene Muscular Dystrophy is still unknown and the present treatment is based on symptom alleviation to improve the quality of life. However, future gene therapy may be a future prospect (Nenshi and Strode 4). Physical indulgence is recommended since sedentary existence aggravates the myopathy, therefore physiotherapy may be useful to maintain function and strength of the muscle. Orthopaedic devices including braces and wheelchairs, may promote mobility and capacity to self care.

Nevertheless, according to a recent study cited by Strode and Nenshi 3), use of immunosuppressant such as prednisone can alleviate the velocity of muscle dystrophy and its related weakness for a short while. In fact prednisone is recommended for patients above the age of 5 to reduce auto immune destruction of the damaged muscle fibres. In addition, when those who have been diagnosed as suffering from Duchene Muscular Dystrophy are enrolled in an established support group, this enables the victims to share related experiences and problems with their counterparts who also suffer from their particular disorder. However, the death prognosis of this disease is usually 25 years of age.

Conclusion

Although Duchene muscular dystrophy is relatively the commonest form of muscular dystrophy, research scientists have made some little advancement in the management and treatment of this defect. For instance with the recent appreciation of the associated cardiopulmonary complication and the improvement of the respiratory support has helped to increase DMD patients’ life expectancy to about 20 to 25 years, and for some cases more than this. However, presently the prognosis stands at poor, with small function capacity and death occurrence of below 30 years.

Works Cited

Anderson, Louise and Bushby, Katherine. Muscular Dystrophy: Methods and Protocols (Methods in Molecular Medicine). Totowa, NJ: Humana Press, 2001. Print.

Deconinck, Nicolas and Dan, Bernard. Pathophysiology of Duchenne Muscular Dystrophy: Current Hypotheses. Pediatric Neurology, 36.1(2007): 1-7.

Nenshi, Rahima and Strode, Kelly. How much do you know about duchenne muscular dystrophy? Clinical quiz, 2. 1(2004): 1-4.

Wu, Joyce. Association of duchenne muscular dystrophy with autism spectrum disorder. J Child Neurol, 20(2005): 790-795.

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NerdyRoo. (2022, March 17). Duchenne Muscular Dystrophy and Its Pathophysiology. Retrieved from https://nerdyroo.com/duchenne-muscular-dystrophy-and-its-pathophysiology/

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