Page 97 - Recognizing axial spondyloarthritis - Janneke de Winter

cohort is including patients aged ≥16 years with chronic back pain (≥3 months, but ≤2 years) with the onset before the age of 45 years. The local medical ethical committees of the participating sites approved the study and all participants gave their written informed consent. For the present analyses, we used data and DNA of the baseline visit of patients included in the Leiden Universitary Medical Center and the Academic Medical Center Amsterdam. We used the central reading results of radiographs and MRI of the sacroiliac joints (14). We compared patients with axSpA (diagnosed by a rheumatologist and fulfilling the ASAS axSpA criteria) with non-SpA CBP patients (diagnosed by a rheumatologist as not having axSpA).
We included 310 patients of the SPACE cohort, including 94 axSpA patients (30.3%) and 216 CBP controls (69.7%). In short, 42 of the 94 axSpA patients were male vs. 61 of the 216 CBP patients (44.7% vs. 28.2%, p=0.005). Of the 94 axSpA patients, 81 were HLA-B*27 positive vs. 32 of the 216 CBP controls (86.2% vs. 14.8%, p<0.0001). The mean age at inclusion of the axSpA patients was 30.5±8.8 years and 31.1±8.2 years of the CBP patients (p=0.57). The mean back pain duration was 14.5±8.1 months in the axSpA patients and 13.6±9.0 months in the CBP patients (p=0.30). Twenty-three of the 94 axSpA patients and 2 of the 216 CBP patients fulfilled the radiographic criterion of the modified New York (mNY) criteria (24.7% vs. 1.0%, p<0.0001). Missing values were ≤ n=1 except for sacroiliitis on MRI (missing n=24), radiographic sacroiliitis (n=13), BASDAI (n=26).
HLA typing
AxSpA patients and controls underwent low-resolution HLA-C typing by a DNA- based technique using sequence-specific oligonucleotides which involved polymerase chain reaction (PCR) amplification of the HLA-C region (Invitrogen, Washington, DC, USA). For the donors enrolled with DKMS, high resolution typing results were available for HLA-B and -C based on Sanger Sequencing or NGS (15). For the SPACE participants enrolled in Leiden, LIFECODES HLA SSO Typing kits were used (Imucor Norcross GA, USA).
HLA-C expression analysis
For the analysis of HLA-C expression, we included patients of the exploratory cohort (24 AS patients and 40 healthy controls), supplemented by 27 AS patients from GESPIC. Peripheral blood mononuclear cells (PBMCs) were isolated from heparinized peripheral blood of 51 patients with AS and 40 healthy controls through density gradient centrifugation using Lymphoprep Ficoll-Isopaque (Axis- Shield, Oslo, NO). RNeasy Micro Kit (Qiagen, Venlo, Netherlands) was used to extract RNA from PBMCs according to the manufacturer’s instructions. RNA concentration was determined with the Nanodrop (Nanodrop Technologies, MA, USA) and reversely transcribed into cDNA (Fermentas, MA, USA). Quantitative real-time PCR was performed on StepOnePlusTM Real-Time PCR System (Applied Biosystems, MA, USA) using TaqMan gene expression assays
HLA-C*07 IN AXIAL SPA
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