A goodness-of-fit test for the polygenic threshold model: application to multiple sclerosis.

Recently it has been suggested that multiple sclerosis may be a multifactorial disorder. We found in British Columbia 364 families (sibship size greater than or equal to 2) in which at least on sibling was diagnosed as having "clinically definite" multiple sclerosis. The data were tested for goodness-of-fit to the multifactorial model using an analysis that considers various parameters including ascertainment probability heritability, and sex-dependent prevalence rates. The results suggest that multiple sclerosis does not fit the multifactorial model. As an alternative genetic model we propose that a major gene could be responsible for at least a portion of the cases of multiple sclerosis.