1. X-linked Muscular Dystrophy Sonja Li, Nancy Liu, Yu Chen Amy Sung, Michelle Tam PHM142 Fall 2014 Instructor: Dr. Jeffrey Henderson

2. What is muscular dystrophy?  Genetic disease affecting skeletal muscles  Characterized by progressive muscle weakness and wasting, and loss of motor skills  X-linked recessive most common: Duchenne and Becker  More than 1 in 3500 males born  Onset age from infancy to adulthood  Most end up wheelchair-bound

3. Duchenne muscular dystrophy  Most common type: 1 in 3500  Early onset: signs appear before 6 years of age  Delayed development of motor skills  Weakness/fatigue  Difficulty in keeping balance  Pseudohypertrophy  Contractures  Wheelchair dependent by ~12 years of age

4. DMD - Gower Maneuver

5. Becker muscular dystrophy  Milder form of Duchenne  1 in 18,518 males  Onset age: 5 to 15 years of age  Loss of muscle mass and motor skills  Weakness/fatigue  Pseudohypertrophy  Contractures  Wheelchair dependent by 25-30

6. Other Conditions Caused  Scoliosis  Curvature due to contractures and muscle weakness  Cardiac  Dilated cardiomyopathy  Arrhythmia  Shortness of breath and fatigue  Respiratory  Progressive weakening of the diaphragm  Cognitive (non-progressive)

7. Dystrophin  Predominant DMD transcript in striated muscle  Gene mutations, deletions or duplications result in a loss of expression  Rod shaped, cytoplasmic  Forms dystrophin-glycoprotein complex (DGC) http://upload.wikimedia.org/wikipedia/commons/6/64/PBB_Protein_DMD_image.jpg

8. Dystrophin Domains  C-terminal end  Cysteine rich domain  Links to glycoprotein complex  Central rod-like domain  Triple α-helical coiled-coil  N-terminal actin binding domain

9. Dystrophin-Glycoprotein Complex Serves as a link b/w extracellular matrix and subsarcolemmal cytoskeleton Protects the sarcolemma against stress during muscle contraction or stretch Dystroglycan: interacts with Cys-rich domain and EC matrix Syntrophin: directly binds to dystrophin C-terminus Sarcoglycan complex: subcomplex of four single transmembrane glycoproteins

10. Normal Muscle Duchenne Muscular Dystrophy Degeneration in DGC leads to tearing of sarcolemma, causing a disturbance in CK and Ca2+ concentrations

11. Causes of Muscular Dystrophy  Muscular dystrophy = mutation of DMD gene  Inability to produce functional dystrophin protein  Constant muscle contraction and relaxation → weaken + destroy muscles  Two types of muscular dystrophy  1. Becker muscular dystrophy – inability to produce functional dystrophin  Dystrophin – not 100% non-functional  Limited function → less severe  2. Duchenne muscular dystrophy – inability to produce dystrophin  No dystrophin production/production of only non-functional dystrophin  No function → more severe

12. Causes of Muscular Dystrophy  Main cause = parents  X-linked disease – caused by mutation in X-chromosome  Inherited from parents  Recessive mutations  Females affected only if both X-chromosomes mutated  Single mutation = enough functional dystrophin produced  Usually unaffected → carrier of disease  Double mutation = affected, but unlikely  Males – single X-chromosome  Mutation in X-chromosome = no dystrophin production

13. Inheritance of Muscular Dystrophy  Unaffected carrier mother + unaffected father  Mother = 1 mutated X-chromosome + 1 normal X-chromosome  Father = 1 normal X-chromosome + 1 normal Y-chromosome  1. Unaffected female  Normal X-chromosome from mother + normal X-chromosome from father  2. Carrier female  Normal X-chromosome from father + mutated X-chromosome from mother  Normal X-chromosome = enough functional dystrophin produced  3. Unaffected male  Normal X-chromosome from mother + normal Y-chromosome from father  4. Affected male  Mutated X-chromosome from mother + normal Y-chromosome from father  No normal X-chromosome = no dystrophin production http://mda.org/sites/default/files/X-linked- recessive_chart.jpg

14. Diagnosis  Blood Creatine phosphokinase (CPK) test  Damaged muscles can release creatine kinase into blood. Elevated levels signify muscle injury: trauma or muscular dystrophy.  Electromyography (EMG)  Measuring electric signaling to and from the muscle can rule out neurodegenerative diseases and confirm a muscle disease.  Muscle biopsy  The microscopic analysis of a sample of muscle tissue can identify presence of muscular dystrophies and its form.  Genetic testing  Testing of mutations in muscular dystrophy related genes can determine the exact form of muscular dystrophy.

15. Therapies for Muscular Dystrophy  Physical therapy  Physical and stretching exercises help keep muscles flexible and strong  Respiratory therapy  Monitor respiratory conditions  Occupational therapy  Teach use of assistive devices eg. wheelchairs  Corrective surgery  For certain conditions from muscular dystrophy eg. pacemaker for myotonic muscular dystrophy or heart problems

16. Drug therapy for Duchenne Muscular Dystrophy  No known cure  Drugs effective only in transiently alleviating the symptoms, delaying muscle degeneration and increasing force of strength  Two most common are corticosteroids: deflazacort and prednisone  Both suppress the body’s immune system and release substances which cause inflammation  Mechanisms unknown

17. Prednisone  Common dose is 0.75 mg/kg of body weight per day  Increases utrophin and dystrophin protein expression in some dystrophic muscles to increase muscle strength  Helps increase number of regenerating fibers after injury of skeletal muscle (prone to occur in patients with DMD)  By increasing myoblast and myotube density as well as number of proliferating myoblasts  General effect: loss of ambulation postponed to mid-teens or twenties and better preservation of respiratory and cardiac function  Side effects: weight gain, rounded face (Cushingoid appearance), acne, cataracts, GI symptoms and behavioural changes

18. X-Linked Muscular Dystrophy Summary Overview  Duchenne and Becker muscular dystrophy: most common forms of muscular dystrophy; affects skeletal muscles and cardiac muscles, leading to their degeneration.  Signs and symptoms include: muscle weakness, loss of muscle coordination and balance, pseudohypertrophy, contractures, and Gower’s sign.  Duchenne is more severe, with earlier onset age and quicker progression, while Becker is like a milder form of Duchenne.  Affected patients gradually loses muscle mass and mobility, end up wheelchair bound and have increased motility  Other conditions caused as a consequence of Duchenne and Becker: Scoliosis, Dilated cardiomyopathy, respiratory complications, and cognitive impairments (which unlike other symptoms, is non-progressive) Dystrophin  Mutations, deletions or duplications of the dystrophin gene most frequently result in a loss of dystrophin expression in muscle of patients afflicted with DMD  Consists of 4 domains:  C-terminal end – binds to syntrophin  Cysteine rich domain – links the cytoskeleton to the extracellular matrix via the membrane with dystrophin-associated glycoprotein, dystroglycan  Central rod-like domain – made from a triple α-helical coiled-coil  N-terminal actin binding domain (very short)  Dystrophin works to protect the sarcolemma against stress through a dystrophin-glycoprotein complex  Includes dystroglycan, syntrophin, and sarcoglycan complex  Degeneration in DGC leads to tearing of sarcolemma, causing a disturbance in CK and Ca2+ concentrations Causes  Muscular dystrophy = recessive genetic mutation in X-chromosome → inherited from parents (most likely mother)  Females – affected if only both X-chromosomes mutated → far less likely to have dystrophy  Males – single mutation required (only one X-chromosome) → most cases of muscular dystrophy are males Diagnosis  Ways to diagnose muscular dystrophy include: Blood Creatine phosphokinase/CPK test, EMG test, biopsy, and genetic testing, which is most specific and non-invasive Treatment  Various therapies available to alleviate symptoms of muscular dystrophy include physical, respiratory, speech, occupational and drug therapies.  Drug treatments for Duchenne Muscular Dystrophy:  There is no known cure – medication only helps to alleviate symptoms and delay muscle degeneration  Most common drug used is prednisone, which is a corticosteroid  Active form is prednisolone Prednisone:  Increases utrophin and dystrophin protein expression in some dystrophic muscles – increases muscle strength  Helps increase number of regenerating fibers after injury of skeletal muscle by increasing myoblast and myotube density as well as number of proliferating myoblasts  General effect: loss of ambulation postponed to mid-teens or twenties and better preservation of respiratory and cardiac function  Side effects: weight gain, rounded face (Cushingoid appearance), acne, cataracts, GI symptoms and behavioural changes

19. References Angelini, C., & Peterle, E. (2013). Old and new therapeutic developments in steroid treatment in Duchenne muscular dystrophy.Acta Myologica, 31(1), 9-15. Baltgalvis, K., Call, J., Nikas, J., & Lowe, D. (2009). The effects of prednisolone on skeletal muscle contractility in mdx mice.Muscle & Nerve, 40(3), 443-454. Becker Muscular Dystrophy. Muscular Dystrophy Canada. Retrieved from http://www.muscle.ca/fileadmin/National/Muscular_Dystrophy/Disorders/Becker_E.pdf Beenakker, E., Fock, J., Van Tol, M., Maurits, N., Koopman, H., Brouwer, O., & Van der Hoeven, J. (2005). Intermittent Prednisone Therapy in Duchenne Muscular Dystrophy: A Randomized Controlled Trial.Archives of Neurology, 62, 128-132. Campellone, J.V. (2014). Becker Muscular Dystrophy. Medline Plus. Retrieved from http://www.nlm.nih.gov/medlineplus/ency/article/000706.htm Calvo, S, et al (2012, February). DMD-associated dilated cardiomyopathy. Genetics Home Reference 2014. Retrieved from http://ghr.nlm.nih.gov/condition/dmd-associated-dilated-cardiomyopathy Calvo, S, et al (2012, February). Duchenne and Becker Muscular Dystrophy. Genetics Home Reference. Retrieved from http://ghr.nlm.nih.gov/condition/duchenne-and-becker-muscular-dystrophy Causes/Inheritance. Muscular Dystrophy Association 2014. Damon, S., et al (2007). Prevalence of Duchenne/Becker Muscular Dystrophy Among Males Aged 5--24 Years --- Four States, 2007. Centres for Disease Control and Prevention. Retrieved from http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5840a1.htm Ervasti, J. M. Structure and Function of the Dystrophin-Glycoprotein Complex. Madame Curie Bioscience Database 2000. Haldeman-Englert (2014). Duchenne Muscular Dystrophy. Medline Plus. Retrieved from http://www.nlm.nih.gov/medlineplus/ency/article/000705.htm Learning about Duchenne Muscular Dystrophy (2013, April 18). National Human Genome Research Institute. Retrieved from http://www.genome.gov/19518854 Merlini, L., Cicognani, A., Malaspina, E., Gennari, M., Gnudi, S., Talim, B., & Franzoni, E. (2003). Early prednisone treatment in Duchenne muscular dystrophy. Muscle & Nerve, 27, 222-227. Muscular Dystrophy (1995). Cleveland Clinic. Retrieved from http://my.clevelandclinic.org/health/diseases_conditions/hic_muscular_dystrophy Nicolas, A. et al. Becker muscular dystrophy severity is linked to the structure of dystrophin. Human Molecular Genetics 2014; 23: 1-13. Signs and Symptoms of Muscular Dystrophy. MDA. Retrieved from http://mda.org/disease/duchenne-muscular-dystrophy/signs-and-symptoms Signs of Duchenne. Parent Project Muscular Dystrophy. Retrieved from http://www.parentprojectmd.org/site/PageServer?pagename=understand_about_signs Straub, V., & Campbell, K. P. Muscular dystrophies and the dystrophin-glycoprotein complex. Current Opinion in Neurology 1997; 10: 168-175. What are the treatments for muscular dystrophy? (2012, November 11). Retrieved November 16, 2014, from http://www.nichd.nih.gov/health/topics/musculardys/conditioninfo/Pages/treatment.aspx