Multiple sclerosis, or M.S.,affects an estimated 1.2 million people worldwide. The progressive disease leaves many of its victims unable to walk unassisted. It mostly strikes women of northern European descent.
M.S. is an auto-immune disorder, caused when the patient's own immune system attacks the myelin sheath that covers human nerve cells. Myelin plays a vital role in speeding nerve impulses to the rest of the body and its destruction can eventually cause disability.
Researchers have long suspected that M.S. is caused in people who are predisposed to the disease by a combination of inherited genetic mutations and an environmental trigger, such as a viral infection or living in temperate climates since the disease is rare in those of African and Middle Eastern descent who live close to the Equator.
Now, a team of scientists has discovered that some people with genetic mutations for M.S. in their DNA never develop the disease. They conducted an exhaustive genetic analysis of three sets of identical twins - including two female pairs - and found no biological explanation for why, in 30 percent of the cases, one twin developed MS and the other one did not.