Absence of rheumatoid arthritis in a rural Nigerian population.

A 2-stage population screening survey of 2,000 inhabitants of 2 rural townships in southern Nigeria was undertaken. No case of rheumatoid arthritis (RA) was discovered in those responding, although 3 cases of inflammatory polyarthritis were found. One of these individuals satisfied the modification of the American College of Rheumatology classification tree criteria that allows for missing radiographic data. Simultaneous monitoring, during a 4-month period, of the local health clinic serving the townships also failed to reveal a case of RA. Three (5.5%) of 55 individuals tested were positive for rheumatoid factor, a rate lower than in previous surveys of rural West African populations. Further immunogenetic investigation of that subsample from this population, using HLA oligonucleotide typing, suggested that HLA-DR4 was rare (1/55). Further, although HLA-DR1 was present in 7 (13%), 6 had the DRB1*0102 variant seen in black populations and not thought to be associated with RA. Our study confirmed the findings of others that rural African groups have extremely low rates of RA. In addition HLA genes containing the RA associated "shared epitope" are also relatively infrequent and might explain this reduction in RA prevalence.