What causes muscular dystrophy?

Muscular dystrophy is a genetic condition, which is brought about by a mutated gene. Most of the time genetic mutations occur for no obvious reason; there are many different types of mutation, which affect the body’s cells and contribute to problems with different functions and systems in the body. Muscular dystrophy can be caused by a spontaneous mutation; this is not the most common cause but it explains why people who have no family history of the disorder sometimes inherit MD.

Muscular dystrophy can also be brought about courtesy of a recessive disorder present at birth or a dominant recessive disorder; a recessive disorder requires a gene that is mutated to be inherited from both parents, while a dominant disorder only requires one gene that is mutated to be inherited. Dominant recessive disorders are more common because they only require one mutated gene to be passed onto the child; if one of your parents has the mutated gene, there is 50 percent chance of you getting muscular dystrophy and there is 25 percent chance of you having the disorder if both your parents are carrying the mutated gene.

Often, different types of muscular dystrophy have different causes; these are outlined below:

• Duchenne MD: Duchenne MD is caused by a defective gene in the X chromosome; this means it can only be passed on by the mother. Duchenne MD may also be brought about by spontaneous mutation. Duchenne MD affects the gene which produces dystrophin, a protein which sits below the sarcolemma, which is protective membrane over the muscle fibres. When there is a lack of dystrophin, the sarcolemma is very fragile and susceptible to tearing. If the membrane tears, calcium can enter the fibre and activate enzymes which start to break down the protein; this result in the muscle fibres growing weaker and eventually dying.
• Myotonic muscular dystrophy: myotonic muscular dystrophy is a dominant disorder which affects the gene that produces a protein called kinase; the gene also has a three step instruction known as a triple repeat sequence, which is repeated too many times in people with myotonic muscular dystrophy.
• Becker MD: this form is very similar to Duchenne MD but it affects the structure of the dystrophin, rather than the amount that is produced.
• Limb-girdle MD: most types of this form of muscular dystrophy are caused by a recessive disorder.
• Oculopharyngeal MD: this form of muscular dystrophy is caused by a dominant recessive disorder.
• Facioscapulohumeral MD: this is caused by a dominant recessive order, which affects the set of genetic instructions contained in the cells.