Concordant and discordant associations between rheumatoid arthritis, systemic lupus erythematosus and ankylosing spondylitis based on all hospitalizations in Sweden between 1973 and 2004.

Objectives: To quantify the sibling risk of RA, SLE and AS. To analyse the concordant and discordant associations between RA, SLE and AS.

Methods: Follow-up study of all individuals and their siblings born in or after 1932 and hospitalized for RA, SLE or AS between 1973 and 2004 (32 yrs).