Racial predilection in multiple sclerosis.

Comparisons between the geographic distribution of multiple sclerosis and the habitats of various racial groups showed that racial factors alone could not explain the increase in prevalence of the disease with latitude. Racially similar groups living in different areas had different frequencies of multiple sclerosis. Conversely, racially different groups, living in the same area, had similar prevalence rates of multiple sclerosis. Moreover, migrants moving from one environment to another at a young age (before adolescence) appeared "to acquire" the risk of multiple sclerosis of the new environment. These observations suggest than an environmental factor independent of race influenced the risk of acquiring multiple sclerosis. Nonetheless, some genetic factors associated with race may also be implicated, for example, HL-A tissue antigens (perhaps by virtue of a common association with the immune response (Ir) gene), the Gm and Inv immunoglobulin characteristics and skin pigmentary characteristics (perhaps through interactions between pigmentation and calcium metabolism). The specific environmental factors determining risk of multiple sclerosis and the mechanism whereby the racial (genetic) factors may influence risk remain to be elucidated.