Expanding the Genetic Framework: Insights into Non-HLA-B27 Contributions to Axial Spondylarthritis

<i>Background and Objectives:</i> Spondylarthritis is a complex group of inflammatory diseases closely associated with the HLA-B27 antigen. However, the role of non-HLA-B27 alleles in the disease's pathogenesis has gained significant scholarly attention in recent years. <i>Case presentation</i>: This case study presents a 49-year-old male with a history of progressive inflammatory back pain, characterized by morning stiffness and restricted spinal mobility developed over several years. Initially presenting with non-specific symptoms, the patient eventually experienced persistent axial pain and deteriorating functional limitations, which required further evaluation. Radiographic imaging supported the diagnosis of ankylosing spondylitis (AS) by identifying bilateral sacroiliitis. HLA genotyping revealed a negative result for HLA-B27 but positive results for HLA-B13 and HLA-B37. This finding serves as a foundation for exploring alternative genetic factors contributing to spondylarthritis (SpA). HLA-B13 and HLA-B37 exhibit structural and functional similarities to HLA-B27, particularly in their peptide-binding grooves. This resemblance may lead to overlapping peptide repertoires and increased T cell cross-reactivity. Moreover, these alleles belong to overlapping cross-reactive groups (CREGs) and share the Bw4 epitope. This suggests that they may contribute to disease pathogenesis via similar mechanisms, such as molecular mimicry and the dysregulation of natural killer (NK) cell interactions, as observed in HLA-B27. <i>Conclusions</i>: This case emphasizes the necessity of expanding diagnostic criteria to incorporate non-HLA-B27 markers, particularly for patients who are HLA-B27-negative. Enhancing our understanding of the roles of alternative genetic markers can improve diagnostic accuracy, enable personalized treatment approaches, and enhance outcomes for the diverse SpA patient population.