Genome-Wide Association Analysis Reveals Genetic Heterogeneity of Sjögren's Syndrome According to Ancestry.

OBJECTIVE: The Sjögren's International Collaborative Clinical Alliance (SICCA) is an international data registry and biorepository derived from a multisite observational study of participants in whom genotyping was performed on the Omni2.5M platform and who had undergone deep phenotyping using common protocol-directed methods. The aim of this study was to examine the genetic etiology of Sjögren's syndrome (SS) across ancestry and disease subsets. METHODS: We performed genome-wide association study analyses using SICCA subjects and external controls obtained from dbGaP data sets, one using all participants (1,405 cases, 1,622 SICCA controls, and 3,125 external controls), one using European participants (585, 966, and 580, respectively), and one using Asian participants (460, 224, and 901, respectively) with ancestry adjustments via principal components analyses. We also investigated whether subphenotype distributions differ by ethnicity, and whether this contributes to the heterogeneity of genetic associations. RESULTS: We observed significant associations in established regions of the major histocompatibility complex (MHC), IRF5, and STAT4 (P = 3 × 10-42 , P = 3 × 10-14 , and P = 9 × 10-10 , respectively), and several novel suggestive regions (those with 2 or more associations at P < 1 × 10-5 ). Two regions have been previously implicated in autoimmune disease: KLRG1 (P = 6 × 10-7 [Asian cluster]) and SH2D2A (P = 2 × 10-6 [all participants]). We observed striking differences between the associations in Europeans and Asians, with high heterogeneity especially in the MHC; representative single-nucleotide polymorphisms from established and suggestive regions had highly significant differences in the allele frequencies in the study populations. We showed that SSA/SSB autoantibody production and the labial salivary gland focus score criteria were associated with the first worldwide principal component, indicative of higher non-European ancestry (P = 4 × 10-15 and P = 4 × 10-5 , respectively), but that subphenotype differences did not explain most of the ancestry differences in genetic associations. CONCLUSION: Genetic associations with SS differ markedly according to ancestry; however, this is not explained by differences in subphenotypes.

The SSB-positive/SSA-negative antibody profile is not associated with key phenotypic features of Sjögren's syndrome.

OBJECTIVE: To determine whether the Sjögren's syndrome B (SSB)-positive/Sjögren's syndrome A (SSA)-negative antibody profile is associated with key phenotypic features of SS. METHODS: Among registrants in the Sjögren's International Collaborative Clinical Alliance (SICCA) with possible or established SS, we compared anti-SSA/anti-SSB reactivity profiles against concurrent phenotypic features. We fitted logistic regression models to explore the association between anti-SSA/anti-SSB reactivity profile and each key SS phenotypic feature, controlling for potential confounders. RESULTS: Among 3297 participants, 2061 (63%) had negative anti-SSA/anti-SSB, 1162 (35%) had anti-SSA with or without anti-SSB, and 74 (2%) anti-SSB alone. Key SS phenotypic features were more prevalent and had measures indicative of greater disease activity in those participants with anti-SSA, either alone or with anti-SSB, than in those with anti-SSB alone or negative SSA/SSB serology. These between-group differences were highly significant and not explained by confounding by age, race/ethnicity or gender. Participants with anti-SSB alone were comparable to those with negative SSA/SSB serology in their association with these key phenotypic features. Among SICCA participants classified with SS on the basis of the American-European Consensus Group or American College of Rheumatology criteria, only 2% required the anti-SSB-alone test result to meet these criteria. CONCLUSIONS: The presence of anti-SSB, without anti-SSA antibodies, had no significant association with SS phenotypic features, relative to seronegative participants. The solitary presence of anti-SSB antibodies does not provide any more support than negative serology for the diagnosis of SS. This serological profile should thus be interpreted cautiously in clinical practice and potentially eliminated from future classification criteria.

Associations between salivary gland histopathologic diagnoses and phenotypic features of Sjögren's syndrome among 1,726 registry participants.

OBJECTIVE: To examine associations between labial salivary gland (LSG) histopathology and other phenotypic features of Sjögren's syndrome (SS). METHODS: The database of the Sjögren's International Collaborative Clinical Alliance (SICCA), a registry of patients with symptoms of possible SS as well as those with obvious disease, was used for the present study. LSG biopsy specimens from SICCA participants were subjected to protocol-directed histopathologic assessments. Among the 1,726 LSG specimens exhibiting any pattern of sialadenitis, we compared biopsy diagnoses against concurrent salivary, ocular, and serologic features. RESULTS: LSG specimens included 61% with focal lymphocytic sialadenitis (FLS; 69% of which had focus scores of ≥1 per 4 mm²) and 37% with nonspecific or sclerosing chronic sialadenitis (NS/SCS). Focus scores of ≥1 were strongly associated with serum anti-SSA/SSB positivity, rheumatoid factor, and the ocular component of SS, but not with symptoms of dry mouth or dry eyes. Those with positive anti-SSA/SSB were 9 times (95% confidence interval [95% CI] 7.4-11.9) more likely to have a focus score of ≥1 than were those without anti-SSA/SSB, and those with an unstimulated whole salivary flow rate of <0.1 ml/minute were 2 times (95% CI 1.7-2.8) more likely to have a focus score of ≥1 than were those with a higher flow rate, after controlling for other phenotypic features of SS. CONCLUSION: Distinguishing FLS from NS/SCS is essential in assessing LSG biopsies, before determining focus score. A diagnosis of FLS with a focus score of ≥1 per 4 mm², as compared to FLS with a focus score of <1 or NS/SCS, is strongly associated with the ocular and serologic components of SS and reflects SS autoimmunity.