A locus on chromosome 9p predisposes to a specific disease manifestation, acute anterior uveitis, in ankylosing spondylitis, a genetically complex, multisystem, inflammatory disease

Objective. Uveitis or intraoeular inflammation is a major cause of visual loss. Acute anterior uveitis (AAU) affects similar to40% of patients with ankylosing spondylitis (AS) but also affects patients with no evidence of spondylarthritis. We sought to determine whether a unique genetic region could be implicated in a specific manifestation-AAU-of a multisystem, inflammatory, genetically complex disease, AS. Methods. Individuals from families multiplex for AAU were genotyped at 400 markers representing the ABI PRISM linkage map MD-10, and at the HLA-B, DRB1, DQA1, DQB1, and DPB1 alleles. Among the family members with AAU, 76 affected sibpairs were analyzed (6 without concomitant AS, 12 discordant for AS, and 58 concordant for AS). Two-point and multi-point nonparametric linkage analyses were performed, and 1-parameter allele-sharing model logarithm of odds (LOD) scores were determined. Results. As previously reported for AS, linkage at the major histocompatibility complex region (chromosome 6p21) was evident, exhibiting the highest multi-point LOD score (4.96 at marker HLA-B). Strong linkage was seen at a region on chromosome 9p21-9p24, with a LOD score of 3.72 at marker D9S157. When compared with a companion cohort of AS families, the linkage at this region was found in association with AAU but not with AS. A third region on chromosome Iq23-1q31 was observed to have suggestive linkage (LOD 2.05 at marker D1S238), which overlaps with a region associated with AS. Conclusion. This is the first study in which a genetic region for AAU has been identified by genome-wide scan. Even though AS was highly prevalent in this cohort of families, a locus at chromosome 9p21-9p24 was identified that uniquely associates with AAU. Identifying the genetic perturbation at this region may advance our understanding of the mechanisms involved in tissue-specific pathology of complex inflammatory diseases.