We do not yet know the answer to this question. The current hypothesis is that the disease appears in those individuals who have a genetic predisposition to react to some infectious agent in the environment such as a virus or bacterium. This means that the disease is not genetically transmitted in the same way as hair or eye colour, for example. There seems to be a combination of genes that makes one person more susceptible to the agent(s) than someone else with a different genetic makeup. While several different viruses and bacteria have been studied for their possible role in MS, the trigger(s) have not yet been found. Environmental and psychological factors may play a part that we do not yet understand. We do know, however, that MS is not a contagious disease and you do not need to be concerned about transmitting MS to those around you.
Wrongly programmed immune cells enter the CNS, causing inflammation in the brain, spinal cord, and/or optic nerves. It is this inflammation that can cause damage to the protective myelin coating around the nerve cells, producing scars (also called plaques or lesions) that interfere with nerve transmission. While many of these scars may have no apparent effect, others are responsible for the various symptoms of MS. Each person’s symptoms will vary depending on the particular location(s) where the scarring (demyelination) occurs. The possible symptoms of MS include: fatigue, changes in vision, stiffness, weakness, imbalance, sensory problems such as numbness, tingling, and pain, changes in bladder and/or bowel function, sexual changes, emotional changes, speech difficulties, and problems with thinking and memory. Fortunately, most people develop only a few of these symptoms over the course of their MS, and most are able to manage their symptoms with assistance and support.