Pathophysiology week 09

What’s Wrong ?

Each cell in our body contains a core structure, a nucleus. Each nucleus contains chromosomes made up of tightly woven strands of dioxyribonucleic acid (DNA). Each cell contains 46 chromosomes which are organized in 23 pairs of which 22 pairs are non-sex (autosomes) and one pair determines the sex of the individual, male (XY) and female (XX). In each 23 pairs, one chromosome is inherited from the father and one chromosome from the mother. Genes are segments of DNA that determine our specific traits such as hair color, blood type etc. that can be inherited from generation to generation. With gene mutation occurs, alternations occur in the DNA and result in genetic disorders. In the following scenario, a concerned mother finds out why her little Jimmy has Duchenne Muscular Dystrophy.
Jimmy is a 4 y.o. boy who has a quick smile and has always been very active. Lately, however, his mother notices that he is more awkward when he walks or runs. In addition Jimmy is having trouble getting up from the floor and often pushes on his legs as he stands up. Jimmy’s mother makes an appointment with his pediatrician.
The pediatrician takes a family history and tests Jimmy’s muscles, takes a muscle biopsy and then does a DNA test. Jimmy’s CK (creatine kinase) levels are elevated and the muscle biopsy confirms that the muscles themselves are causing the problem. The DNA testing confirms that Jimmy has Duchenne Muscular Dystrophy (DMD). The pediatrician recommends to Jimmy’s mother that Jimmy’s two sisters have DNA testing done also.
Duchenne Muscular Dystrophy is a genetic disorder characterized by progressive skeletal muscle (voluntary muscles) degeneration resulting in muscle wasting and weakness. The main cause is a flawed gene on the X chromosome (X-linked recessive) that fails to produce a protein dystrophin. Dystrophin is one of many proteins found in the membrane surrounding each muscle fiber and is needed to keep muscle cells working properly. Without dystrophin protein, necrosis of the cell occurs. DMD affects mostly boys, rarely girls due to the X-linked pattern. Males (XY) only inherit a single X-linked gene and not a second X chromosome to over-ride a flawed recessive trait that occurs with females (XX). A father with DMD will not pass on DMD to his sons because he only gives the Y gene,however, he will pass on his X recessive gene to his daughters, making them carriers to pass on to their children. The mothers who have at least one x-gene with DMD will have a 50% chance in passing the defective recessive gene to her sons and 50 % of her daughters will become carriers. Sometimes dystrophin gene mutation takes place inside the egg of females, therefore, increasing her future pregnancies risk for DMD disorder. (Gould, B. E., pg 585-586, 2011)(nlm.nih.gov, 2012)(mda.org, 2012)(genome.gov, 2012)
Jimmy’s physician recommended that Jimmy’s older sisters have DNA test done to verify if they also may be a carriers. Accordingly to the Muscular Dystrophy Association, a minority of female carriers may manifest weak muscles in their back, legs, and arms and fatigue easily and others may have heart problems that may cause SOB or fatigue after mild exercise . At a later time, when Jimmy’s sisters are older and become pregnant, they can have a prenatal diagnostic test called chorionic villus test done at 12 weeks of gestation. This test is done to determine whether the fetus could have abnormalities or inherited or genetic disorders such as DMD. (Gould, B. E., p.586, 2011) (merckmanuals.com, 2012)
In the early stages, DMD affects muscles in the shoulders, arms, hip and thigh areas. Weakness in the pelvic girdle may lead to difficulty in rising from the floor (“Gower’s maneuver”); a technique where the child pushes with hands climbing up the legs in order to become erect. Children with DMD are usually late in walking and when they do walk, their gait may look like waddling or unsteady; toddlers may have large calf muscles (pseudo-hypertrophy). DMD children may also have difficulties in climbing stairs, maintaining balance, and difficulty in raising the arms. (Gould, B. E., pg 585-586, 2011) (mda.org, 2012)
DMD boys usually show symptoms as early as 3 years old. Around 7-12 years of age DMD children start to have weakness in ambulation. In their teens, children may need assistance or mechanical assistance in use of their arms, or legs, or trunk activities along with additional problems with respiratory and heart muscles (cardiomyopathy) because of the lack of dystrophin. (mda.org, 2012)
Jimmy’s symptoms became more apparent at age 4. At this age his mother noticed Jimmy’s was having more awkward movements during walking or running. Jimmy also start having trouble getting up from the floor and often pushes on his legs as he attempts to stand. Jimmy’s pediatrician carefully reviews family history, and tests Jimmy’s muscles in order to establish DMD history and muscular weakness pattern. The physician obtains CK ( creatine kinase), does a muscle biopsy and obtains a DNA test in order to confirm the diagnosis and eliminate other potential diseases. An elevated CK enzyme means muscle are being destroyed by an abnormal process. The muscle biopsy confirms that the muscles themselves are causing the problem. The DNA testing confirms that Jimmy has Duchenne Muscular Dystrophy.
Since DMD eventually effects all voluntary muscles, including the heart and respiratory muscles, survival is rare past the early thirties. Treatment goals for Jimmy will be to maintain comfort, encourage activity and promote/maintain function and prolong life expectancy. As muscles deteriorate, contractures can result and become severe, restricting mobility and flexibility. Physical therapy (PT) initiated will incorporate scheduled passive and active range of motion exercises in order to post pone contractures and prevent tendons from shortening. Resistance exercise are not advised because it may accelerate muscle damage. Hydrotherapy creates excellent exercise without resistance. Braces ( orthoses) may be used for lower limbs for support, and keep them flexible and stretched only when ambulation is becoming more difficult, however, while Jimmy is ambulating, an ankle-foot orthoses may be worn only during sleep to prevent contractures. Children who are able to stand or walk beyond of the age of 13 are less likely to require spinal surgery and have delayed contractures. When it comes time where Jimmy experiences difficulty in walking, wheel chair availability will help to conserve energy and provide more independence. Passive and active assisted exercises will continue to for comfort, aesthetics and contracture prevention. Spinal curvature such as scoliosis (s-curve) or lordosis (sway-back curve) will be dealt with through exercise to maintain straightness as long as possible. If scoliosis becomes severe, surgery with rod placement may have to be done. (enmc.org, 2012)
Medications such as corticorticoid may be started to improve muscle strength and slow the progression of the disease and usually initiated when physical performance plateaus. Prednisone is the choice medication in the United States. Prednisone oral dosage may be started at 0.75 milligrams per kilogram of weight daily or every other day. Reduction of dosage may depend on side effect such as excess weight gain, behavior problems, cataracts, or osteoporosis. Immunity to chicken pox needs to be established prior to initiating Predisone. (mda.org, 2012)

References

Anonymous. (2012). Duchenne muscular dystrophy
Retrieved March 3, 2012, from NLM NIH website
http://www.nlm.nih.gov/medlineplus/ency/article/000705.htm

Anonymous. (2012). Duchenne muscular dystrophy
Retrieved March 3, 2012, from MDA website
http://www.mda.org/disease/dmd.html

Anonymous. (2012). Duchenne muscular dystrophy
Retrieved March 3, 2012, from MDA website
http://www.mda.org/publications/fa-dmdbmd.html

Anonymous. (2012). Duchenne muscular dystrophy
Retrieved March 3, 2012, from Genome website
http://www.genome.gov/19518854

Anonymous. (2012). Prenatal Dia Gnostic Testing
Retrieved March 3, 2012, from Merchmanuals website
http://www.merckmanuals.com/home/womens_health_issues/genetic_disorders_detection/prenatal_diagnostic_testing.html

Anonymous. (2012). Duchenne muscular dystrophy [PDF]
Retrieved March 3, 2012, from Genome website
http://www.enmc.org/uploaded/publicatie/manage.DMD.pdf

Gould, B. E. (2011) Chapter 24
(pp. 585-586), Path physiology for the Health Professions, 4th Edition. Saunders Learning, printed in United States.

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