Epidemiological aspects of family studies in rheumatoid arthritis.

The study of multicase families is of value in the analysis of genetic association between rheumatoid arthritis and markers such as HLA. There are a number of ways that multicase families arise but it is likely that the affected individuals within these families are not genetically distinct from sporadic cases. More problematic, however, is the nature of the disease itself. Its variable presentation, at any age, and the existence of self-limiting forms renders classification of individuals within families complex. In the absence of continuous life-long observation the only reasonable alternative is to use all available data for analysis and not be constrained by rigid criteria developed for other purposes.