Association study of the HLA class I system with psoriatic arthritis in Southern Tunisia: a case-control study

Introduction/objectives: Psoriatic arthritis (PsA) is a chronic inflammatory rheumatism belonging to the spondyloarthritis family. It is a multifactorial disease whose genetic determinism is still poorly understood. It is favored by environmental factors in genetically predisposed individuals. This study aims to investigate the association of HLA-A, HLA-B, and HLA-C alleles with PsA and its various manifestations in patients from Southern Tunisia.

Patients and methods: A case-control association study was conducted involving 48 PsA patients and 123 controls. HLA-A and HLA-B typing was performed using microlymphocytotoxicity complement-dependent assays, and HLA-C typing was done using polymerase chain reaction-sequence specific primer.

Results: Positive associations were confirmed for HLA-B27 and -C*06 alleles with PsA in our Southern Tunisian population with a more pronounced association in cases of -C*06 homozygosity. The HLA-B*27-C*02 and HLA-B*50-C*06 haplotypes were significantly more frequent in PsA patients, whereas the HLA-B*35-C*04 haplotype was negatively associated with PsA. Specific HLA alleles were linked to disease manifestations: -C04 with female sex, -B27 with familial spondyloarthritis, and -B17 with sporadic PsA. Cervical spine involvement was associated with -C02, and hip involvement with -B35 and -C02. Uveitis was linked to -C02 and -B27. A negative association was observed between a BASFI score > 4 and the presence of -B45 and -C07.

Conclusion: The HLA class I system contributes to PsA susceptibility in the Southern Tunisian population. Key Points • This is the first study exploring the association between HLA class I alleles and psoriatic arthritis in Southern Tunisia. • HLA-B27 and -C06 alleles are strongly associated with PsA, with a more pronounced effect in -C06 homozygosity. • Specific HLA alleles are linked to clinical manifestations: -B27 is associated with familial PsA, -B17 with sporadic PsA, and -B35 with hip involvement. • These findings provide insights into the genetic contribution to PsA pathophysiology in Southern Tunisia and highlight the role of HLA alleles in specific disease features.