A genetically inherited progressive disease of the central nervous system. MS occurs as a consequence of one's own immune system attacking the insulating sheath that normally protects neurons. Symptoms range from numbness and tingling to paralysis. There is a loss of motor and cognitive functions. The gene(s) responsible for MS are incompletely penetrant in that the onset of the disease is apparently triggered by a virus and possibly other environmental factors. There is a correlation between the amount of sunlight that children are exposed to and the likelihood that they will develop MS later in life. People who spend much of their first 16 years in tropical and subtropical regions of the world are much less likely to develop this disease than those who live in far northern and far southern regions of our planet. It is believed that the lack of abundant sun exposure early in life is somehow responsible for the later onset of MS.