The familial nature of rheumatoid arthritis.

Considerable emphasis is currently being placed on the immunogenetics of rheumatoid arthritis (RA). The observation that inherited factors are important in RA is by no means new, however. As far back as 1806 William Heberden in discussing 'chronical rheumatism' asked, 'Is this not in some degree hereditary?'.' The first published attempt to answer this question was by Kroner in 1928,' who reported RA in four generations of women in one family. Like Kroner, all rheumatologists can quote families with a marked occurrence of RA. Yet a 1984 study concluded that 'familial aggregation of rheumatoid arthritis is weak'.2 How can these apparently contradictory observations be explained? How large is the genetic contribution to RA? What are the inherited susceptibility factors in RA? Why does RA seem to congregate in some families and not in others?