Whole-Exome Sequencing Reveals Distinct Genetic Profiles of Palindromic Rheumatism.

OBJECTIVE: Previous studies underline the genetic susceptibility in the pathogenesis of Palindromic Rheumatism (PR), but the known PR loci only explain partially the disease's genetic background. We aim to genetically identify PR by whole exome sequencing (WES).

METHODS: This multi-center prospective study was conducted in ten Chinese specialized rheumatology centers between September 2015 and January 2020. WES was performed in a PR cohort (185 PR cases and 272 healthy controls). PR patients were divided in to ACPA- PR and ACPA+ PR subgroups according to ACPA titer (cut-off value: 20UI/I). Whole-exome association analysis was conducted for the WES data. HLA imputation was used to type HLA genes. The polygenic risk score (PRS) was further used to measure the genetic correlations between PR and Rheumatoid Arthritis (RA) , and the genetic correlations between ACPA- PR and ACPA+ PR.

RESULTS: A total of 185 patients with PR were enrolled. ACPA was found positive in 50 out of 185 PR patients (27.02%), and 135 PR patients were ACPA negative (72.98%). 8 novel loci (ACPA- PR: ZNF503, RPS6KL1, HOMER3, HLA-DRA; ACPA+ PR: RPS6KL1, TNPO2, WASH2P, FANK1) and three HLA alleles (ACPA- PR:HLA-DRB1*0803, HLA-DQB1; ACPA+ PR: HLA-DPA1*0401) were found to be associated with PR surpassing genome-wide significance (p<5x10-8 ). Furthermore, PRS analysis showed PR and RA were not similar (R2 <0.025), while ACPA+ PR and ACPA- PR had a moderate genetic correlation (0.38<R2 <0.8).

CONCLUSION: This study demonstrated the distinct genetic background of ACPA-/+ PR patients. Additionally, our findings strengthened that PR and RA were not genetically similar.