AIF-1 gene does not confer susceptibility to Behçet's disease: Analysis of extended haplotypes in Sardinian population

Background BehcEet's disease (BD) is a polygenic immune-mediated disorder characterized by a close association with the HLA-B∗51 allele. The HLA region has a strong linkage disequilibrium (LD) and carries several genetic variants (e.g. MIC-A, TNF-α genes) identified as associated to BD because of their LD with HLA-B∗51. In fact, the HLA-B∗51 is inherited as part of extended HLA haplotypes which are well preserved in patients with BD. Sardinian population is highly differentiated from other Mediterranean populations because of a distinctive genetic structure with very highly preserved HLA haplotypes. Patients and methods In order to identify other genes of susceptibility to BD within the HLA region we investigated the distribution of human Allograft Inflammatory Factor-1 (AIF-1) gene variants among BD patients and healthy controls from Sardinia. Six (rs2736182; rs2259571; rs2269475; rs2857597; rs13195276; rs4711274) AIF-1 single nucleotide polymorphisms (SNPs) and related extended haplotypes have been investigated as well as their LD within the HLA region and with HLA-B∗51. Overall, 64 BD patients, 43 HLA-B∗51 positive healthy controls (HC) and 70 random HC were enrolled in the study. Results HLA-B∗51 was the only allele with significantly higher frequency (pc = 0.0021) in BD patients (40.6%) than in HC (9.8%). The rs2259571TAIF-1 variant had a significantly reduced phenotypic, but not allelic frequency in BD patients (72.1%; pc = 0.014) compared to healthy population (91.3%). That was likely due to the LD between HLA-B∗51 and rs2259571G(pc= 9E-5), even though the rs2259571Gdistribution did not significantly differ between BD patients and HC. Conclusion No significant difference in distribution of AIF-1 SNPs haplotypes was observed between BD patients and HC and between HLA-B∗51 positive BD patients and HLA-B∗51 positive HC. Taken together, these results suggest that AIF-1 gene is not associated with susceptibility to BD in Sardinia.