A GENETIC-BASIS FOR FAMILIAL AGGREGATION IN MULTIPLE-SCLEROSIS

GENETIC-environmental interactions probably underlie spontaneous human autoimmune disorders, a category of complex traits thought to include multiple sclerosis (MS)(1). The geographical distribution and familia r aggregation of this disease have often been ascribed to the role of infectious agents(2), but there is no consensus, Increased family risk s range from 300-fold(3,4) for monozygotic twins to 20-40-fold(5) for biological first-degree relatives over the general population prevalen ce of 0.1% (ref. 6). We screened a population-based sample of 15,000 i ndividuals with MS by using standardized, personally administered ques tionnaires to identify adopted index cases and/or those who had adopte d relatives, The frequency of MS among first-degree non-biological rel atives living with the index case was no greater than expected from Ca nadian population prevalence data and significantly less than for biol ogical relatives, These findings indicate that familial aggregation of MS is genetically determined: no effect of shared environment was det ectable.