Arthritis-related gene clusters on chromosomes (Chr.) 6, 15, and 19. The peaks on the Chr. 6, 124-megabase (Mb) locus (#12) includes complement receptor genes and C-type lectin superfamily (Clecsf) genes, the Chr. 15, 79-Mb locus (#13) includes colony-stimulating factor 2 receptor beta (Csf2rb) genes, and the Chr. 19, 11-Mb locus (#14) includes membrane spanning four-domain, subfamily A (Ms4a) genes. Expanded views of these loci in 1-Mb scale and hierarchical clustering of the expression levels of these genes are shown.