The proportion of RA sibs sharing 0, 1, or 2 parental alleles for PTPN22 is 0.26 (181 pairs), 0.51 (362 pairs), and 0.23 (167 pairs), respectively, and does not differ from the IBD distribution 0.25; 0.5; 0.25 expected under no linkage. This evidence concerns the gene PTPN22 and rheumatoid arthritis.