Identification of a common genetic susceptibility profile for autoimmune diseases

The genetic factors of autoimmune diseases have been difficult to define due to the high polymorphism of the candidate genes found so far, and the population variability of these. Moreover, in most studies, autoimmune diseases have been considered individually and, in few, in the same population. In the present family-based association study, a genomic scan was performed using 393 microsatellite markers, spaced every 10 cM, in 986 individuals belonging to 242 families from the same Colombian population, where at least one relative had an autoimmune disease [rheumatoid arthritis=36, systemic lupus erythematosus=59, type 1 diabetes mellitus=114 and multiple autoimmune syndrome=33]. Transmission imbalance test was used in the pedigrees. A common association was observed in all diseases with the 3q26.1 locus (D3S1763). Disease-specific and some shared associations were also observed for two of the diseases. Further fine mapping studies will allow us to establish the responsible gene and its associated polymorphism, as well as to evaluate it functionally as a common mechanism of autoimmunity. Our results confirm that autoimmune diseases despite differing phenotypically may have similar etiological mechanisms and indicate that there is a common genetic background for autoimmunity.