Sarcoidosis is a polygenic immune disorder with predominant manifestation in the lung. Genome-wide linkage analysis previously indicated that the extended major histocompatibility locus on chromosome 6p was linked to susceptibility to sarcoidosis. Here, we carried out a systematic three-stage SNP scan of 16.4 Mb on chromosome 6p21 in as many as 947 independent cases of familial and sporadic sarcoidosis and found that a 15-kb segment of the gene butyrophilin-like 2 (BTNL2) was associated with the disease. The primary disease-associated variant (rs2076530; P(TDT) = 3 x 10(-6), P(case-control) = 1.1 x 10(-8); replication P(TDT) = 0.0018, P(case-control) = 1.8 x 10(-6)) represents a risk factor that is independent of variation in HLA-DRB1. BTNL2 is a member of the immunoglobulin superfamily and has been implicated as a costimulatory molecule involved in T-cell activation on the basis of its homology to B7-1. The G --> A transition constituting rs2076530 leads to the use of a cryptic splice site located 4 bp upstream of the affected wild-type donor site. Transcripts of the risk-associated allele have a premature stop in the spliced mRNA. The resulting protein lacks the C-terminal IgC domain and transmembrane helix, thereby disrupting the membrane localization of the protein, as shown in experiments using green fluorescent protein and V5 fusion proteins.

Linkage analyses have implicated chromosome 7p21.3 as a susceptibility region for inflammatory bowel disease (IBD). Recently, the mouse phenotype with diarrhea and goblet cell dysfunction caused by anterior gradient protein 2 dysfunction was reported (European patent WO2004056858). The genes encoding for the human homologues AGR2 and AGR3 are localized on chromosome 7p21.3. The gene structures were verified and mutation detection was performed in 47 IBD patients. A total of 30 single nucleotide polymorphisms (SNPs) were tested for association to ulcerative colitis (UC, N ¼ 317) and Crohn's disease (CD, N ¼ 631) in a German cohort and verified in a UK cohort of 384 CD and 311 UC patients. An association signal was identified in the 5 0 region of the AGR2 gene (most significant SNP hcv1702494, nominal P TDT ¼ 0.011, P case/control ¼ 0.0007, OR ¼ 1.34, combined cohort). The risk haplotype carried an odds ratio of 1.43 in the German population (P ¼ 0.002). AGR2 was downregulated in UC patients as compared to normal controls (Po0.001) and a trend toward lower expression was seen in carriers of the risk alleles. Luciferase assays of the AGR2 promoter showed regulation by the goblet cell-specific transcription factors FOXA1 and FOXA2. In summary, AGR2 represents an interesting new avenue into the etiopathophysiology of IBD and the maintenance of epithelial integrity.

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