Group+6+Duchenne+Muscular+Dystrophy

​​ = = = //**DUCHENNE MUSCULAR DYSTROPHY **// =



= = =I. GENERAL DESCRIPTION OF THE BIRTH DEFECT. = = = = = Duchenne Muscular Dystrophy (DMD) is one of the nine muscular disorders, and one of the most common. It generally affects males; females can be carriers without any symptoms, although there are known mild to severe cases of DMD in females ( Bushby et al., 2009). This genetic, degenerative disease occurs in 1 in 3,500 male births and is caused by the absence of Dystrophin - in 1987 identified as the protein responsible for keeping muscle cells intact. This disease is named after a French physician, Guilliame Duchenne, who first coined the word 'dystrophy' (after the Greek word roots, 'dys-' meaning abnormal, diseased or faulty, and '-trophy' which refers to nutrition or growth ) in the 1860s, when he noticed that the muscles in some young boys were weakening and wasting away.



Despite its relatively recent discovery, Emery (1988) has stated "muscular dystrophy has afflicted Man from earliest times" (p. 7). Its history goes all the way back to the time of ancient Egypt, as depicted on wall paintings (i.e. Egyptian relief painting on the wall of a tomb, from the 18th Dynasty of the New Kingdom around 1500 BC).

DMD initially affects the voluntary, proximal muscles, like the muscles of the pelvic and pectoral girdles. The distal voluntary muscles, as well as the heart and breathing muscles are affected later as the disease progresses. As of today there is no cure for Duchenne Muscular Dystrophy and the disease is 100% fatal. Survival beyond the early 30s is rare. The treatment of DMD focuses on slowing down its effects by prolonging mobility, preventing complications and improving the general quality of life. The only medications currently available as DMD treatment are Glucocorticoids, which slow the decline in muscle strength and function ([]).

= = =II. ETIOLOGY, SYMPTOMS AND DIAGNOSIS. =

= = As mentioned before, DMD is a genetic disorder that is characterized by the lack of dystrophin in muscles. But what exactly is dystrophin?

Brody (2006) stated "Dystrophin is a protein which binds to the muscle membrane cells and helps to maintain the muscle cell structure. It acts like a shock absorber for the muscle cells, and enables them to return to their initial state. The gene that produces this protein is also known as the dystrophin gene, and it is the largest [and among the most complex] in the human genome." Mutations in the dystrophin gene disturb dystrophin production, hence DMD.



The dystrophin gene is carried on the X-chromosome. Therefore, the disease is often called an X-linked disorder. Every male possesses one X chromosome from his mother and one Y chromosome from his father. Every female has two X chromosomes, one from each parent. Boys are more susceptible to damage to the dystrophin gene as they have only one X chromosome. "When a boy is diagnosed with Duchenne MD, his body is not able to produce any dystrophin. Without fully functional dystrophin, muscle cells within the body gradually weaken and eventually die" (Duchenne Muscular Research Fund, 2010)

This disorder often occurs in people without a known family history of the condition and is not specific to any ethnic group. As previously stated, it is considered a sex-linked disorder. "The sons of females who are carriers of the disease (women with a defective gene but no symptoms themselves) each have a 50% chance of having the disease. The daughters each have a 50% chance of being carriers" (Google Health, 2010). The reason they are not affected in the majority of cases is that females have an extra X-chromosome to fall back on if one of the chromosomes is damaged.



Boys born with DMD can show signs of the disorder as early as infancy, though the majority of cases are diagnosed later, most often when the deteriorating muscles visibly affect motor skills. The progressive muscle weakness manifests itself in difficulties performing motor skills (such as running, hopping and jumping) and frequent falls. The loss of walking ability usually occurs before age 12 and death occurs around age 25, typically from lung disorders (complications in the late stages of the disease).

**Most common symptoms include:**


 * Muscle weakness (rapidly worsening)
 * Progressive difficulty walking
 * Gowers's Manoeuvre (see picture below)
 * Pseudohypertrophy (overdeveloped calves)
 * Contractures (loss of elasticity) in Achilles tendons
 * Lordosis
 * Scoliosis
 * <span style="font-family: Georgia,serif;">Fatigue and overall weakness
 * <span style="font-family: Georgia,serif;">Clumsiness
 * <span style="font-family: Georgia,serif;">Respiratory problems
 * <span style="font-family: Georgia,serif;">Speech/intellectual handicaps



<span style="color: #800000; font-family: Georgia,serif;">**The four stages associated with the disease are:**


 * 1. Early Phase (diagnosis through age 7)**

<span style="color: #800000; font-family: Georgia,serif;">
 * <span style="font-family: Georgia,serif;">calves may seem overdeveloped
 * <span style="font-family: Georgia,serif;">clumsiness and falling a lot
 * <span style="font-family: Georgia,serif;">difficulty walking, running, or climbing stairs due to weakness in the legs and pelvis
 * <span style="font-family: Georgia,serif;">struggle to lift head, or has a weak neck
 * <span style="font-family: Georgia,serif;">help needed getting up from the floor
 * <span style="font-family: Georgia,serif;">walking with legs apart
 * <span style="font-family: Georgia,serif;">standing and walking with chest and stomach stuck out (or has a sway back)
 * <span style="font-family: Georgia,serif;">using the Gower maneuver to get up from the floor (walking hands up the legs instead of standing straight up, due to weak leg muscles)
 * <span style="font-family: Georgia,serif;">difficulty or impossibility of jumping from a standing position
 * 2. Transitional Phase (6-12 years)**

<span style="color: #800000; font-family: Georgia,serif;">
 * <span style="font-family: Georgia,serif;">trouble walking (quadriceps have grown weaker)
 * <span style="font-family: Georgia,serif;">walking on the balls of the feet or on toes with a slight, rolling gait.
 * <span style="font-family: Georgia,serif;">sticking the belly out and throwing the shoulders back to keep balance while walking
 * 3. Loss of ambulation (8-14 years)**


 * <span style="font-family: Georgia,serif;">in need of a wheelchair for at least part of the time, as mobility becomes more difficult (loss of ability to walk by age 12)
 * <span style="font-family: Georgia,serif;">tiring easily due to weakened muscles
 * <span style="font-family: Georgia,serif;">significant loss of skeletal muscle strength (teen years)
 * <span style="font-family: Georgia,serif;">activities involving the arms, legs, or trunk of the body require assistance or mechanical support
 * <span style="font-family: Georgia,serif;">ability to use fingers retained in most cases
 * <span style="font-family: Georgia,serif;">heart problems due to an enlarged heart

<span style="color: #800000; font-family: Georgia,serif;">**4. Adult Stage (15+ years)**

<span style="font-family: Georgia,serif;"> Early diagnosis is crucial for this fast progressing disease. Children that are diagnosed at a young age (early stage of the disease) can receive better preventive care and treatment that will contribute substantially to the quality of their life. Furthermore, Speech-Language Pathologists can play a very important role in this process (for more details see "overall effects on speech"). Diagnosis includes physical examination by a pediatrician, genetic testing as well as testing levels of creatine kinase - an enzyme present in the muscles. High levels of it in the blood indicate muscle damage.
 * <span style="font-family: Georgia,serif;">skeletal muscle problems
 * <span style="font-family: Georgia,serif;">heart muscle problems (threat to both health and life due to damage and loss of respiratory muscles; heart muscle - myocardium begins to deteriorate; risk of a heart attack): symptoms include:
 * <span style="font-family: Georgia,serif;">shortness of breath
 * <span style="font-family: Georgia,serif;">fluid in the lungs
 * <span style="font-family: Georgia,serif;">swelling in the feet and lower legs (caused by fluid retention)

= = = = =<span style="color: #800000; font-family: Georgia,serif;">III. SYSTEMS REVIEW. =

<span style="font-family: Georgia,serif;">Initially DMD was treated more as a physical than mental disorder. Muscle deterioration and weakening of all vital functions seemed removed from the nervous system. Essex & Roper (2001) noted "30% of boys with Duchenne's muscular dystrophy have major learning difficulties.[...] Dystrophin is needed for continuing normal muscle function, but its isoforms are thought to have a function in the central nervous system" (p. 37).

Wahl (1997) stated "By the early 1990s, researchers began to see more than they had expected. The dystrophin gene wasn't just a muscle protein gene. There was also a brain form of dystrophin, made from the same gene, but in slightly different way" (paragraph 1).

Considering this, in speech production, only the respiratory system is more impaired than the nervous system by DMD. Multiple abnormalities have been found, including :
 * <span style="font-family: Georgia,serif;">cortical atrophy
 * <span style="font-family: Georgia,serif;">neuronal loss
 * <span style="font-family: Georgia,serif;">abnormalities in dendrites

<span style="font-family: Georgia,serif;">Lidov (1996) postulated, <span style="font-family: Georgia,serif;">"Given the central role of neocortical and hippocampal function in cognition and memory, a localization of the DMD gene product to these structures is a reasonable basis for a genetic defect producing mental retardation" (p. 71).

Many DMD patients have a diminished IQ, with studies consistently showing the average of groups afflicted with DMD being significantly lower than healthy control groups. Anderson (2007) says "The average IQ of a boy with DMD is 85" ( p. 5). Sometimes the disorder results in mental retardation, though it is important to note that the effects of DMD on the nervous system can vary widely and are not always an obstacle to communication, as some mentally impaired DMD patients have been found to have normal-range verbal IQs. (Tracy, 1995) According to Coletta (2007), the core areas affected in DMD patients seem to include "verbal short-term memory, and phonological language processing...findings for cognitive functions show notable, significant differences...in...vocabulary tests" (p. 62).

Because of these effects from DMD, one of the warning signs for DMD is a child who shows a delay in developing speech. A specific milestone is a child's inability to use at least 10 recognizable words before the age of 2. (Parsons, 2004) = = = = = = = = = = =<span style="color: #800000; font-family: Georgia,serif;">**B) RESPIRATORY SYSTEM** =

<span style="font-family: Georgia,serif;">Of the systems afflicted by Duchenne Syndrome, the respiratory system is among the most affected. Emery (1988) states that over 90% of deaths result from pulmonary infection and respiratory failure (p. 235)<span style="font-family: Georgia,serif;">. Therefore, it is crucial to preserve the optimal respiratory function and adequately treat occurring respiratory infections to prolong and sustain the life of a person diagnosed with the disease.

According to Newson-Davis (1980) "Respiratory muscle weakness is often a cause of disability in patients with muscular dystrophy, and in many cases contributes significantly to the cause of death. A period of ventilatory insufficiency may be followed by ventilatory failure" (p. 135).

Throughout the different stages of the disease, the decrease of oxygen in the blood and the increase of carbon dioxide make the exchange of air very difficult for the lungs.

As a result of these respiration difficulties the following symptoms can occur:

<span style="font-family: Georgia,serif;"> <span style="color: #000000; font-family: Georgia,serif;">Due to breathing problems, a <span style="font-family: Georgia,serif;"> tracheostomy tube may need to be surgically placed in the trachea. Other people with the disease may need a respirator.
 * <span style="font-family: Georgia,serif;">headaches
 * <span style="font-family: Georgia,serif;">mental lapses
 * <span style="font-family: Georgia,serif;">difficulty concentrating and staying awake during the day
 * <span style="font-family: Georgia,serif;">hyperventilation in sleep (especially in patients with diaphragm paralysis late in the disease)
 * <span style="font-family: Georgia,serif;">intermittent airway obstruction in sleep

Although respiratory function usually remains normal until around age 10, Newson-Davis (1980) observed that<span style="font-family: Georgia,serif;"> "as diaphragm's strength declines, the importance of the role of intercostal muscles increases. When the intercostal and abdominal muscles's weakness progresses, it reduces the effectiveness of the cough" (p. 135). As it was said before, this may predispose the person with Duchenne Syndrome to terminal pulmonary infection (the weakened muscles responsible for coughing may permit bacteria and viruses to grow ,<span style="font-family: Georgia,serif;"> which often allows a simple cold to quickly progress into deadly pneumonia).

=<span style="color: #800000; font-family: Georgia,serif;">C) PHONATORY SYSTEM = = = ​<span style="font-family: Georgia,serif;">Two recent, independent studies show that the phonatory system, especially the intrinsic muscles of the Larynx, might not be affected by the lack of dystrophin. (Thomas, B., Joseph, G., Adkins, T., Andrade, F., Stemple, J., 2008) "Despite the absence of dystrophin in the mdx laryngeal muscles, membrane damage, inflammation, necrosis, and regeneration were not detected in the assays performed.[...] The purpose of the study was to determine the effects of dystrophin deficiency on 2 intrinsic laryngeal muscles, the posterior cricoarytnoid and the thyroarytenoid, in the mouse model." (Thomas et al., 2008, Their conclusion was that "these muscles are one of only few muscle groups spared in this model of dystrophin deficiency." (Thomas et al., 2008, 586) Fry, Stemple, Andreatta, Harrison & Andrade (2010) reinforced that the intrinsic laryngeal muscles did in fact deviate substantially from the skeletal muscles.

Research concludes that the laryngeal muscles are largely unaffected by the resultant loss of dystrophin from DMD, implying the presence of countermeasures against dystrophin deficiency in this group of muscles. (Thomas et al, 2008)

=<span style="color: #800000; font-family: Georgia,serif;">D) ARTICULATORY SYSTEM =

= = <span style="font-family: Georgia,serif;">The presence of DMD has lead to dysphagia (difficulty swallowing) in many patients, which increases in severity as the patient ages (Hanayama et al., 2008). Hanayama et al. (2008) observed that the weakness of the oropharyngeal muscles results in a failure to completely swallow food, especially in the case of solid food as opposed to liquids and semi-solid substances (such as jelly) (p. 519). Despite this, laryngeal penetration remains rare, most likely due to the resistance of the laryngeal muscles to the effects of DMD. However, due to the deterioration of the respiratory system, many patients with DMD have difficulty coughing, making it a challenge to clear the airway.

In advanced cases, patients with DMD exhibit malnutrition, though studies have shown that dysphagia develops before this occurrence. Hanayama et al. (2008) recommend dysphagia testing be regularly performed on patients with DMD. (p. 521)

The facial muscles are weakened and waste away from DMD, with facial weakness being one of the first symptoms and observable in the patient's difficulty in whistling, closing his eyes, and smiling. (Harvard Health Publications, 2006). The tongue is afflicted by a condition called myotonia, which in muscles results in difficulty returning to a relaxed state and prolonged contraction. (Harvard Health Publications, 2006). This makes the patient unable to properly articulate many sounds in speech, such as the "plosive" sounds like ///p/// and fricatives like ///f///.

Another effect of DMD on this system is a diminished capacity to recognize and duplicate facial expressions, though Hinton (2008) suggests that this is due more to similarities in brain structure between DMD patients and those affected by autism, leading to "modestly impaired facial affect recognition" (p. 8). .

=<span style="color: #800000; font-family: Georgia,serif;">E) AUDITORY SYSTEM =

= = <span style="font-family: Georgia,serif;">The Auditory System seems not to be affected in DMD. Problems with processing spoken language and decoding the phonological code received have a have a root in neurological rather than auditory disorders.

= = =<span style="color: #800000; font-family: Georgia,serif;">IV. OVERALL EFFECT ON SPEECH PRODUCTION =

= = <span style="font-family: Georgia,serif;">After reviewing the systems affected by DMD, it is clear that Duchenne Muscular Dystrophy is a multilevel and multisystem disease. It requires interdisciplinary management and a close collaboration of specialists (such as Speech-Language Pathologists) from different areas to give the patient a better quality of life.

From the perspective of speech production, the two most affected systems are the respiratory system and the nervous system. Both have great effects on speech, though they differ in how they contribute to speech production and in their handicaps.

The system that shows the earliest signs of the disease is the nervous system, and more precisely its products - speech and memory. Bushby et al. (2009) made the observation that "Delayed acquisition of early language milestones is common in boys who have DMD" (p. 184) Speech and language would be without meaning without the central nervous system. If impaired (as it is by DMD) speech production will be affected, such as in a delay in speech acquisition. This symptom is noticeable much earlier than the deterioration of muscle tissue. It is important for an infant with DMD to receive treatment at this early stage of life. An important role of a Speech-Language Pathologist is to be able to recognize the symptoms in a child with DMD who has been brought in for speech therapy. As speech and global developmental delays are some of the symptoms of DMD which occur before the locomotor symptoms, they are ideal for an early diagnosis. It is crucial in sustaining the best possible quality of life of those affected, since DMD remains among the fatal genetic diseases.

The failing respiratory system will affect speech production at its power source - without an intact diaphragm and other skeletal muscles involved in respiration, the energy needed for speech production is gone. At this point the state of functionality of muscles in other systems (like the phonatory or articulatory) is secondary. Perfectly functioning laryngeal muscles or the muscles of the face and tongue will not be able to contribute much towards speech production if there is insufficient subglottal pressure to initiate phonation.

Thomas et al. (2008) inferred, "One mechanism whereby the disease may exert influence upon voice production is via its influence on the diaphragm, the major muscle of respiration. Over time, the disease causes marked changes in the structure and function of the diaphragm (Beck et al., 2006; Stedman et al., 1991). As the diaphragm and its associated muscles of respiration drive the phonatory system, limitations in these muscles can be expected to bring about alterations in voice production" (p. 586-587).

According to J  ournal of Speech, Language & Hearing Research performed by the   American Speech-Language-Hearing Association in 2008, the influence of the Duchenne Muscular Dystrophy on speech and voice production has received little attention in the literature overall, due to most research addressing the deterioration of skeletal muscles.

<span style="color: #b84700; font-family: Georgia,serif; font-size: 15pt;">//**References**//

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