Genetic analysis in rheumatoid arthritis.

The use of heritability studies, haplotype sharing, and lod score analysis are reviewed. Twin and family studies show that any genes conferring susceptibility to rheumatoid arthritis must have a relatively low penetrance. This is a serious obstacle to linkage analysis in families. Where there is a population association, as with DR4, studies of haplotype sharing by affected sibs may yield more information if the observations are compared with the sharing predicted from the population association.