Genetic epidemiology of multiple sclerosis: a survey.

The possible role of genetic factors in the etiology of multiple sclerosis (MS) has been debated for over a century. It is now clear that genetic and environmental interactions must exist. It is likely that MS susceptibility is under the control of several genes encoded both within and outside the major histocompatibility complex (MHC). It is therefore unlikely that MS has a purely transmissible cause for these and other reasons, including the low concordance rate in dizygotic twins, low concordance rate in conjugal pairs, negative birth order in multiplex MS sibships, the relatively high rate of MS in second- and third-degree relatives of MS patients, and the identification of groups resistant to MS in otherwise high-risk areas.