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Description and Cause
Myotonic dystrophy, the most common adult form of muscular dystrophy, is an inherited neuromuscular disorder in which muscles contract but have decreasing power to relax along with other physical and intellectual implications. Myotonic dystrophy is caused by a mutation on the myotonin protein kinase gene, involving unstable trinucleotide repeats on chromosome 19; the greater the length of expansion, the more severe are the characteristic features. It follows an autosomal dominant pattern of inheritance. There can be considerable variability among affected individuals, even within the same family. There appears to be increased severity of symptoms and decreased age of onset within families as the condition is transmitted to younger generations. The disease is rarely congenital, most often developing some time after birth. However, affected infants may demonstrate severe hypotonia in the newborn stage. Half of affected individuals show visible signs by age 20, while half do not develop symptoms until after age 50.
Electromyography will generally support clinical suspicion of the disease, and diagnosis may be confirmed by DNA probe analysis on blood.
Note: Except in congenital cases, physical disability rarely becomes severe until fifteen to twenty years after the onset of symptoms. The higher the age of onset, the slower is the progression of the disease and the less serious are the consequences.
MEDICAL MANAGEMENT CONSIDERATIONS
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Note: These considerations are in addition to the normal medical care provided to an individual without Myotonic Dystrophy. Although many recommendations can be addressed through clinical examination by the primary care provider, a multidisciplinary team approach (primary care physician, neurologist, pulmonologist, physical therapist, occupational therapist, nurse, orthopedist, social worker) is recommended for persons with Myotonic Dystrophy. Multidisciplinary care may be obtained through programs such as California Children Services (CCS) or clinics funded by the Muscular Dystrophy Association.
Because most cases of myotonic dystrophy are adult-onset and clinical expression varies so widely, recognition and diagnosis may not be possible until well after birth. In any case, the following should be performed as soon as diagnosis is clinically suspected:
Ongoing (all ages)
Childhood (1 to 13 years, if applicable)
Adolescence and Adulthood (13 years and over)
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Peer-reviewed Journal Articles/Academies
Broughton, R., Stuss D., Kates M., Roberts J., Dunham W. (1990). Neuroopsychological Deficits and Sleep in Myotonic Dystrophy. Canadian Journal of Neurological Sciences, 17(4), 410-5
George, A., Schneider-Gold, C., Zier, S., Reiners, K., Sommer C. (2004) Musculoskeletal Pain in Patients with Myotonic Dystrophy Type 2. Archives of Neurology 61(12). 1938-1942.
Machuca-Tzili, L., Brook, D., Hilton-Jones D. (2005) Clinical and Molecular Aspects of the Myotonic Dystrophies: a review, Muscle & Nerve, 2005 32(1), 1-18
Motlagh, B., MacDonald, J.R., Tarnopolsky M.A. (2005). Nutritional Inadequacy in Adults with Muscular Dystrophy. Muscle & Nerve, 31(6), 173-178.
Phillips, M.F., Harper, P.S. (1997). Cardiac Disease in Myotonic Dystrophy. Cardiovascular Research, 33(1), 13-22.
Ptacek, L.M, et al. (1993). Genetics and Physiology of the Myotonic Muscle Disorders. New England Journal of Medicine, 328(7), 482-489.
Reifer H., Sobel, E. (1998). Contrasts in Clinical Presentation and Genetic Transmission of Myotonic Dystrophy. Journal of the American Podiatric Medical Association, 88(7), 313-322.
Rudnik-Schoneborn S., et al. (1998). Different Patterns of Obstetric Complications in Myotonic Dystrophy in Relation to the Disease Status of the Fetus. American Journal of Medical Genetics, 80(4), 314-321.
Skocyzlas L.J., Langlais R.P., Young R.S. (1985). Mytonic Dystrophy: Review of the Literature and New Radiographic Findings. Dentomaxillofacial Radiology, 14 (2), 101-108.
Wiles, C.M., Busse, M.E., Sampson, C.M., Rogers, M.T., Fenton-May J., van Deursen R. (2005). Falls and Stumbles in Myotonic Dystrophy. Journal of Neurology, Neurosurgery and Psychiatry. Retrieved November 2, 2005.
Special Interest Groups/Other Publications
Bird T.D. (2004) Myotonic Dystrophy Type 1. Retrieved January 23, 2006.
Capute, A. J., Accardo, P.J. (1996). Developmental Disabilities in Infancy and Childhood vol. I. Neurodevelopmental Diagnosis and Treatment. Baltimore: Paul H. Brookes Publishing Co.
Capute, A.J., Accardo, P.J. (1996). Developmental Disabilities in Infancy and Childhood vol II. The Spectrum of Developmental Disabilities. Baltimore: Paul H. Brookes Publishing Co.
Griesemer, D. A., Waheed, N. (1999). Muscular Dystrophy. In M.R. Dambro (Ed.) Griffith’s 5-Minute Clinical Consult. Baltimore: Lippincott Williams & Wilkins, pp. 704-705.
May, P.B. Jr., (1999) Myotonic Dystrophy Developmental Medicine Clinic syllabus. UMD New Jersey, Robert Wood Johnson Medical School. Retrieved January 20, 2006.
Moxley, R.T. (1997). Myotonic Disorders in Childhood: Diagnosis and Treatment. In Carrell-Krussen Symposium invited lecture, Journal of Child Neurology 12(2), 116-129.
RESOURCES FOR FAMILIES
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California Department of Developmental Services
California Regional Centers
European Alliance of Muscular Dystrophy Associations
Exceptional Parent Magazine
March of Dimes Birth Defects Foundation
Muscular Dystrophy Association (USA)
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Theodore A. Kastner, M.D., M.S.
Felice Weber Parisi, M.D., M.P.H.
Mary Ann Lewis, Dr.P.H., R.N., F.A.A.N.
Joan M. Reese, M.D., M.P.H.
Jaime D. Mejlszenkier, MD., F.A.A.N
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This document does not provide advice regarding medical diagnosis or treatment for any individual case, and any opinions or statements contained in this document are not intended to serve as a standard of medical care. Physicians are encouraged to view the considerations presented in this document in light of evolving scientific information. This document is not intended for use by the layperson. Reproduction of this document may be done with proper credit given to California Department of Developmental Services.
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