musculardystrophy

Muscular Dystrophy

Muscular dystrophy (MD) is a group of rare hereditary muscle diseases characterized by progressive skeletal muscle weakness. Lack of or defect in muscle cell structural proteins is the basic cause of MD. A conservative estimate of overall prevalence of MD is 29 per 100,000 population (1 in 3500 or 0.029%)1.

More than 30 muscle disorders with similarities to MD have been identified. Of these, nine diseases listed below are relatively common and Duchenne Muscular Dystrophy is the most common.

Table 1. MD subtypes and responsible defective proteins, shown with estimated prevalence2.

DMD occurs due to the mutation in a gene named Dystrophin (the largest gene identified in human) resulting in deficiency of the muscle protein called dystrophin. A complex of proteins, of which dystrophin is part, work together as an anchor and connects muscle cell's cytoskeleton (structural framework) with the extracellular matrix (lattice of protein molecules outside the cell). Any defect in dystrophin protein compromises the complex from maintaining the structure of skeletal, cardiac and other muscles. Therefore DMD and BMD patients display symptoms distinct for this deficiency. Similarly, defects in proteins listed as 'affected proteins' in the table manifest in various symptoms enabling categorization of subtypes in MD. In a scale of MD severity due to dystrophin protein, DMD occupies the severe end of the MD spectrum while the BMD occupies the other end.

MD is a multi-system disorder showing manifestations in organ systems including heart, nervous systems, endocrine glands (ductless glands), digestive system, eyes, skin and other organs. Weakness and wasting (atrophy) of various voluntary muscles of the body are clinical hallmarks of MD. Depending on MD subtype the disorders affect different sets of muscles and have different disease onset ages, severity and patterns of inheritance. MD is a progressive disorder and most affected individuals require a wheelchair by mid teenage years.

Elevated levels of serum enzyme creatine kinase (CK; also called creatine phosphokinase) is an indication of MD. In conditions such as MD where cellular membrane integrity is compromised, this intracellular enzyme leaks from muscle fibers into blood circulation. In BMD and DMD, CK levels are extremely high compared to normal subjects. Electromyography (EMG; measures muscle electrical potential) using needle electrode is an invasive method (a needle is inserted into the muscle) employed in suspected MD cases, usually when CK level is not significantly elevated. EMG results on MD patients display reduction in amplitude and duration of motor unit potential. EMG also helps to rule out nervous system cause of the muscle weakness. Muscle histology and immunocytochemistry (certain tissue staining tests done under microscope) methods are also used in diagnosis. In cases where these diagnostic methods are not definitive molecular genetic analysis might help in diagnosis.

Prolonged immobilization in MD patients hasten deterioration of muscles. Physiotherapy, physical exercise and being ambulatory help ameliorate MD. Glucocorticoids, a kind of steroid, is used in certain type of MD which prolongs the mobility of MD subjects for about two years. However prolonged steroid administration has several severe side effects. Gene therapy or stem-cell therapy are still in experimental stage and might help in MD subjects in future. Presently no cure for MD is available.

Certain MD subtypes have localized geographic distribution: Fukuyama-type CMD in Japan, Distal MD is most common in Scandinavia, particularly Finland, OPMD in French regions of Canada.

MD in the context of India.

DMD/BMD and LGMD are frequently reported MD cases compared to other subtypes in India. Interestingly, in Britain, people of Indian ethnic background has been identified to have a disproportionately high incidence of DMD compared to Pakistani or other ethnic groups. In contrast, an observation in eastern India (Bihar, West Bengal and Bangladesh) reports a higher incidence of the DMD cases in Muslims compared to Hindu population in that region. However, both these studies recognize paucity in their patient sample size and resulting inability to arrive at a sensible statistical conclusion. A separate report in 1997 'estimated' that there were about 22,000 DMD cases present in India, and more than 2500 cases added every year. There are several published reports on MD subtypes in recent years in India. A comprehensive analysis of these reports, if initiated, might shed some light on true prevalence of MD or MD subtypes in India and the subcontinent as well.

Contributor: Duraiswamy Navaneetham PhD.

Temple University School of Medicine

Philadelphia, PA, USA

Reviewer: Ahmad Syed MD, PhD.

Temple University School of Medicine,

Philadelphia, USA.

Oct. 2009.

1 Commonly cited by most MD researchers, this estimate is from an exhaustive survey on the basis of published MD reports from countries essentially in Europe and North America. Outside this core domain, Israel, Japan and Libya are the only countries represented in this study. Interested readers may refer to: Emery AEH, Population frequencies of inherited neuromuscular diseases - A world survey. Neuromuscular Disorders, 1991; 1:19.

2 Data collected from various published reports on MD are shown. Numbers for MD subtypes other than DMD are based on limited studies and may not be conclusive.

Related organizations in India

Muscular Dystrophy Association India

C/O V.J.Clinic,

New no: 6, (Old 21), Fourth Cross Street,

Sastri Nagar, Adyar

Chennai 600 020, Tamilnadu

Phone: 91-90032 95482

Email: mdaindia.org@gmail.com

http://www.mdaindia.org

Sundaram Medical Foundation

A Network Center of the Cooperative International Neuromuscular Research Group

Shanthi Colony, 4th Ave.