HLA-C*07 in axial spondyloarthritis: data from the German Spondyloarthritis Inception Cohort and the Spondyloarthritis Caught Early cohort.

We aimed to assess the mRNA expression of MHC class 1-related molecules in ankylosing spondylitis (AS) patients vs healthy controls (HCs) and, subsequently, if the absence of HLA-C07 is associated with genetic susceptibility to axial spondyloarthritis (axSpA). HLA-C07 was assessed in (a) an exploratory cohort of 24 AS patients vs 40 HCs, (b) a confirmatory cohort of 113 AS patients and 83 non-radiographic axSpA patients from the GErman SPondyloarthritis Inception Cohort (GESPIC) vs 134,528 German potential stem cell donors, and (c) an early back pain cohort with 94 early axSpA patients vs 216 chronic back pain (CBP) patients from the SPondyloArthritis Caught Early (SPACE) cohort. In the exploratory cohort, 79% of the AS patients were HLA-C07 negative compared to 35% of the HCs (p < 0.001). This difference was confirmed in GESPIC with 73% of AS patients being HLA-C07 negative compared to 50% of the controls (p < 0.0001); 59% of the nr-axSpA patients were HLA-C07 negative. In the SPACE cohort, 70% of the axSpA patients were HLA-C07 negative compared to 44% of CBP patients (p < 0.0001); the association between HLA-C07 negativity and a diagnosis of axSpA was independent from HLA-B27. In conclusion, the absence of HLA-C*07 is associated with genetic susceptibility to axSpA.