Rheumatoid arthritis in the Pima Indians

Objective. To describe the clinical features and familial distribution of rheumatoid arthritis (RA) in the Pima Indians. Methods. From 1965 through 1990, all cases of RA as defined by the American College of Rheumatology (formerly, the American Rheumatism Association) 1987 criteria or all cases of seropositive, erosive disease as defined by the Rome criteria were identified in individuals who were age 20 years and older and were of 50% or more Pima/Tohono-O'odham heritage. Radiographs were reviewed by 2 musculoskeletal radiologists who were blinded to case status. Kinship coefficients were used to evaluate familial aggregation. Results. Eighty-eight RA cases were identified from this population-based sample. Over 66% of the cases had seropositive disease, over 60% had erosive disease, and over 40% had subcutaneous nodules. Of the 88 RA cases, 40 were members of families with more than 1 RA case. The remainder were simplex cases. Conclusion. In this population, clinical markers of severe RA were present in a majority of cases. The presence of familial aggregation for RA in the Pima Indians suggests underlying genetic factors in disease pathogenesis.