Qin-Yi Su ¹ Yan Zhang ² Dan Qiao ³ Xia Song ³ Yang Shi ³ Zhe Wang ³ Chenyan Wang ³ Sheng-Xiao Zhang ^1*

• ¹ Department of Rheumatology, Second Hospital of Shanxi Medical University, Taiyuan, Shanxi Province, China
• ² Shanxi Medcial University, Taiyuan, China
• ³ Shanxi Medical University, Taiyuan, China

Background: Ankylosing Spondylitis(AS) is a connective tissue disease that primarily affects spinal joints, peripheral joints, and paravertebral soft tissues, leading to joint stiffness and spinal deformity. Growing evidence has implicated gut microbiota in regulation of AS, though the underlying mechanisms remain poorly understood. Methods: We conducted a comprehensive search of PubMed, Embase databases, Web of Science, the Cochrane Library, MEDLINE, Wanfang Data, VIP and CNKI from the time the databases were created until July 30, 2023. Meta-analyses were performed using STATA 12.0, a meta-analysis was carried out, and the quality of the literature was assessed by following systematic review guidelines. Results: This systematic review and meta-analysis included 47 studies. Our findings indicate a significant reduction in gut microbial diversity in AS patients, as evidenced by a decrease in both richness and evenness. Specifically, the Shannon index showed a moderate decrease (SMD = -0.27, 95% CI: -0.49, -0.04; P < 0.001), suggesting a less diverse microbial ecosystem in AS patients. The Chao1 index further confirmed this trend, with a larger effect size (SMD = -0.44, 95% CI: -0.80, -0.07; P < 0.001), indicating a lower species richness. The Simpson index also reflected a significant reduction in evenness (SMD = -0.30, 95% CI: -0.53, -0.06; P < 0.001). Additionally, AS patients who received anti-rheumatic combination treatment exhibited a more pronounced reduction in α-diversity compared to untreated patients, highlighting the potential impact of treatment on gut microbiota balance. In terms of specific microbial families, we observed a significant decrease in the abundance of Bifidobacterium (SMD = -0.42, 95% CI: -2.37, 1.52; P < 0.001), which is known for its beneficial effects on gut health. Conversely, an increase in the abundance of Bacteroidetes was noted (SMD = 0.42, 95% CI: -0.93, 1.76; P < 0.001), suggesting a possible shift in the gut microbiota composition that may be associated with AS pathophysiology. Conclusion: Our analysis revealed changes in α-diversity and the relative abundance of specific bacteria in AS. This suggests that targeting the gut microbiota could provide new therapeutic opportunities for treating AS.