But some genes reported to be among the most significantly associated with BD showed extreme reduction in nucleotide diversity, and excess of rare variants (such as DTL, NOD2, FUT2, IL23R, SMARCA2, STX8) only in East Asians, suggesting a unique evolutionary history of these genes in East Asians, where highest BD incidence and prevalence is reported. This evidence concerns the gene IL23R and Behcet disease.