OBJECTIVE: To use high-density genotyping to investigate the genetic associations of acute anterior uveitis (AAU) in patients with and those without ankylosing spondylitis (AS). METHODS: We genotyped samples from 1,711 patients with AAU (either primary or combined with AS), 2,339 AS patients without AAU, and 10,000 control subjects on an Illumina Immunochip Infinium microarray. We also used data for AS patients from previous genome-wide association studies to investigate the AS risk locus ANTXR2 for its putative effect in AAU. ANTXR2 expression in mouse eyes was investigated by real-time quantitative reverse transcription-polymerase chain reaction. RESULTS: A comparison between all patients with AAU and healthy control subjects showed strong association over HLA-B, corresponding to the HLA-B27 tag single-nucleotide polymorphism rs116488202. The association of 3 non-major histocompatibility complex loci, IL23R, the intergenic region 2p15, and ERAP1, reached genome-wide significance (P