We assessed the hypotheses that non-major histocompatibility complex multiple sclerosis (MS) susceptibility loci would be common to sporadic cases and multiplex families, that they would have larger effects in multiplex families, and that the aggregation of susceptibility loci contributes to the increased prevalence of MS in such families.
A set of 43 multiplex families comprising 732 individuals and 211 affected subjects was genotyped for 13 MS candidate genes identified by genome-wide association. A control data set of 182 healthy individuals was also genotyped to perform a case-control analysis alongside the family-based pedigree disequilibrium association test, although this may have been underpowered.
An effect of the IL2RA and CD58 loci was shown in multiplex families as in sporadic MS. The aggregate of the IL2RA, IL7R, EVI5, KIAA0350, and CD58 risk genotypes in affected individuals from multiplex families was found to be notably different from controls (chi(2) = 112, p = 1 x 10(-22)).
Although differences between individual families can only be suggested, the aggregate results in multiplex families demonstrate effect sizes that are increased as compared with those reported in previous studies for sporadic cases. In addition, they imply that concentrations of susceptibility alleles at IL2RA, IL7R, EVI5, KIAA0350, and CD58 are partly responsible for the heightened prevalence of multiple sclerosis within multiplex families.