Duchenne Muscular Dystrophy and Existing Methods of Its Treatment

Muscular dystrophy is a genetic disease that currently has no cure. There are medical treatments and medications that can help ease symptoms and manage the disease. We will discuss further later what these treatments and medications are and how they can help the patient. Let's first briefly discuss the history of muscular dystrophy and how the disease propagates.

Muscular dystrophy comes in various types, one being Duchenne Muscular Dystrophy (DMD), and will be the focus of this discussion. According to an article in Medical News Today (2017) written by Tim Newman, the “symptoms [of Duchenne muscular dystrophy] normally start before a child's third birthday; they are generally wheelchair-bound by 12 years and die of respiratory failure by their early-to-mid-twenties' (Newman, 2017). So, what is muscular dystrophy?

There is a protein found in the skeletal muscle called dystrophin. Dystrophin is a” protein [that] helps anchor various components within muscle cells together and links them all to the sarcolemma” (Newman, 2017). This protein is vital for skeletal muscles to function appropriately including movement and repair. When this protein is missing, the muscle will weaken. In addition to progressively decreasing gross motor skills, there is even more happening on the cellular level. “Pathological changes include the absence of dystrophin at the membrane of the muscle fibers, increased adipose and connective tissue between muscle fibers, increased variability in muscle fiber size, infiltration of inflammatory cells, and centrally located nuclei, which are indicative of degenerating and regenerating muscle fibers” (Lovering, 2005). The absence of dystrophin is linked to genetic mutations to the X chromosome (2017). The “recessive X-linked disorder occurring 1 in every 3500 live male births [is] named after a French neurologist Guillaume Benjamin Amand Duchenne in 1860” (Sinha et al., 2017).

An article in the Journal of Family Medicine and Primary Care (Sinha, 2017) followed a case of a 12-year-old male who’s only complaint at the time was a decayed tooth. The article mentioned the parents of the child told the physician they noticed he was having difficulty climbing stairs, fatigue and falling. “On general physical examination, the child had an obese appearance and presented with difficulty in standing, walking, getting up from sitting position and climbing stairs, proximal weakness, calf hypertrophy, hamstring muscle contracture, and positive Gower's sign” (Sinha, 2017). Gower’s sign was invented in 1879 by a neurologist by the name of Sir William Richard Gowers. This test is used to screen patients for muscle weakness commonly seen in DMD (Chang, 2012).

When a patient is being examined by his or her physician for possible signs of DMD, there are several factors that play into the official diagnosis. Since DMD is a severe disease and can lead to death, physicians use a variety of tools and test like the Gower’s sign, to determine if a patient has DMD or not. Newman (2017) lists several signs and symptoms that are commonly associated with DMD. Some of the early signs of DMD include: “a waddling gait, pain and stiffness in the muscles, difficulty with running and jumping, walking on toes, difficulty sitting up or standing, learning disabilities, such as developing speech later than usual, frequent falls” (2017). These symptoms will progress into more serious problems as time goes on. For example, patients will develop a full inability to walk, limited movement due to shortening of muscles and tendons, difficulty breathing and even cardiac problems because of weakened heart muscles (2017).

In addition to physical examinations of a patient suspected of having DMD, further tests will be ordered to confirm the diagnosis of DMD. These tests may include blood draws, X-Ray and/or CT scan, and even an EMG scan. In the case of the 12-year-old male patient mentioned previously, his physician ordered these tests to be completed. The results were as follows; an analysis of his serum found creatine kinase (CK) levels were elevated in addition to other chemical components. “On electromyographic examination, interference pattern analysis revealed myopathic pattern in the right vastus lateralis suggestive of primary muscle disease” (Sinha, 2017). Based on these finding, the patient’s physician determined a diagnosis of DMD was warranted and was referred for further evaluation and rehabilitation.

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Since there is no cure currently for DMD, there are medication treatments and therapies available for patients with DMD. Patients may be prescribed corticosteroids to help strengthen muscle weakness, however, according to Newman (2017), “long-term use can weaken bones and increase weight gain” (2017). If the patient is experiencing cardiac problems, beta blockers and/or ACE inhibitors may be prescribed to help with symptoms.

In addition to drug therapy, physical therapy can help keep the patient’s muscles flexible for as long as possible. Unfortunately, the muscles will eventually fatigue to a point where there is no longer motion and the limbs will become “fixed in position” (Newman, 2017). To help the patient maintain some mobility, they may be required to use specialized devices like leg braces, canes, walkers and wheelchairs. Since it is inevitable that the patient’s limbs will become immobile, the goal of physical therapy is to prolong the mobility for as long as possible. Newman (2017) suggests, “Standard low-impact aerobic exercises such as walking and swimming can also help slow the disease's progression” (2017).

DMD not only affects the patient’s limbs but can also affect other vital muscles such as the diaphragm, which is necessary to breath. “As the muscles used for breathing become weaker, it may be necessary to use devices to help improve oxygen delivery through the night. In the most severe cases, a patient may need to use a ventilator to breathe on their behalf” (Newman, 2017).

Researchers are currently working to develop long term treatments that may help replace the missing dystrophin in muscle tissue and may even help repair some of the damage DMD causes. An article in Muscular Dystrophy News (2018) written by Marta Figueiredo, announced a promising form of treatment for DMD. Researchers are currently running test trials of microdystrophin gene therapy that “robustly induces the production of a shorter, but functional, version of the dystrophin protein and reduces muscle damage in Duchenne muscular dystrophy (DMD) patients, according to preliminary results of a Phase 1/2 clinical trial” (Figueiredo, 2018). According to Figueiredo (2018), “Microdystrophin is a shorter version of the dystrophin gene, that contains the minimum amount of information needed to produce a functional dystrophin protein. It also directs the delivery of the microdystrophin gene specifically to muscle tissue (while avoiding other tissues), in particular the heart muscle, which is crucial for DMD patients, who frequently die from heart disease” (2018). This clinical research trial has found that microdystrophin gene therapy has increased the dystrophin levels in trial patients while also decreasing the levels of creatine kinase. Figueiredo (2018) stated, “Two months after treatment, all patients showed a significant decrease, more than 87%, in the levels of creatine kinase (CK), an enzyme used as a biomarker for muscle damage. This result suggests that the amount of microdystrophin being produced is effectively protecting the muscle” (2018).

In a more recent research study, a new medication is being investigated through clinical trials. According to IOS Press of Science News (2019), “The investigational drug edasalonexent, an oral NF-κB inhibitor, has the potential to slow the progression of the disease for all patients with DMD” (IOS Press, 2019). Dr. Joanne Donovan, who is following this clinical study suggests, “edasalonexent has the potential to limit disease progression for all patients affected by DMD, regardless of their underlying mutation, and can potentially reduce muscle inflammation and degeneration and enhance muscle regeneration” (IOS Press, 2019).

Even though DMD is rare, based on statistics mentioned previously, it is still very important to gain as much knowledge about the disease and find new ways to treat it. Since there is no cure, researchers are working hard to find new ways to help patients cope with the disease and prolong the use of their muscles. According to the Muscular Dystrophy Association (MDA) (2019), the “MDA has dedicated over $209 million to DMD research, with over $45 million of that investment coming in the past five years alone. The research efforts of thousands of scientists over the course of decades has resulted in many promising leads for potential therapies, some of which are currently being evaluated by the FDA for approval” (MDA.Org, 2019). There is hope that one day a cure will be found.

Resources

1. Chang, R. F., & Mubarak, S. J. (2012). Pathomechanics of Gowers' sign: A Video Analysis of a Spectrum of Gowers' Maneuvers. Clinical Orthopedics and Related Research, 470(7), 1987–1991. doi:10.1007/s11999-011-2210-6. Retrieved online from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3369091/
2. Figueiredo, M. (2018, June 22). Microdystrophin Gene Therapy Shows Promising Interim Results in Phase 1/2 Trial. Muscular Dystrophy News Today. Retrieved online from https://musculardystrophynews.com/2018/06/22/microdystrophin-gene-therapy-shows-promise-early-trial-results/
3. IOS Press. (2019, February 21). New Drug for Duchenne Muscular Dystrophy Clears Phase 1 Clinical Trial Testing in Boys. ScienceDaily. Retrieved online from www.sciencedaily.com/releases/2019/02/190221130242.htm
4. Lovering, R. M., Porter, N. C., & Bloch, R. J. (2005). The Muscular Dystrophies: From Genes to Therapies. Physical Therapy, 85(12), 1372–1388. Retrieved online from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4496952
5. MDA.Org. (2019). Duchenne Muscular Dystrophy. Research and Special Programs. Retrieved online from https://www.mda.org/disease/duchenne-muscular-dystrophy/research
6. Newman, T. (2017, December 18). All About Muscular Dystrophy. Medical News Today. Retrieved online from https://www.medicalnewstoday.com/articles/187618.php.
7. Sinha, R., Sarkar, S., Khaitan, T., & Dutta, S. (2017). Duchenne Muscular Dystrophy: Case Report and Review. Journal of Family Medicine and Primary care, 6(3), 654–656. doi:10.4103/2249-4863.222015. Retrieved online from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5787973/