GENERAL DATA: The clinical manifestations and neuropathological signs of multiple sclerosis have been recognized for more than one hundred years, but the cause remains unknown.
Epidemiology: Multiple sclerosis is not evenly distributed throughout the world. There is an important north-south gradient in the northern hemisphere and inversely in the southern hemisphere; multiple sclerosis is more frequent in the higher altitudes. For a given latitude, there is a difference by ethnic origin. These observations indicate that multiple sclerosis is a multifactorial condition determined by both genetic and environmental factors.
Strategies of genetic studies: Progress in our knowledge of the human genome and statistical analysis techniques have made it possible to search for genetic factors in multiple sclerosis using two complementary approaches. The first is by anonymous screening and the second is to search for a candidate gene. The HLA locus is the only one with an identified predisposing effect for multiple sclerosis. It only accounts for 10 to 20% of the genetic predisposition for multiple sclerosis and many factors remain to be discovered.