By this approach, we narrowed the mapped IBD regions into a single stretch with 2.4 Mb length (0.08% of the genome) at 2p23 (from 27.2–29.5 Mb), which was shared among 5 RA cases and 1 ACPA-positive unaffected subject but ≤6 of 18 ACPA-negative unaffected subjects (Figure 3B right panel). The gene discussed is PRTN3; the disease is rheumatoid arthritis.