Do ethnicity, degree of family relationship, and the spondyloarthritis subtype in affected relatives influence the association between a positive family history for spondyloarthritis and HLA-B27 carriership? Results from the worldwide ASAS cohort

Table 1 Baseline characteristics of chronic back pain patients suspected of axial spondyloarthritis included in the ASAS cohort

Characteristics	Data (N = 594)
Age at baseline, years	33.7 (11.7)
Male sex	276 (46%)
Duration of back pain, years^a	7.1 (9.0)
Self-reported ethnicity
White	348 (59%)
Asian	214 (36%)
Other^b	32 (5%)
IBP (according to experts’ definition)	301/532 (57%)
Good response to NSAIDs^c	274 (46%)
Peripheral arthritis^d	197 (33%)
Enthesitis^d	241 (41%)
AAU^d	53 (9%)
Dactylitis^d	23 (4%)
Psoriasis^d	22 (4%)
IBD^d	8 (1%)
Positive family history according to ASAS definition	135 (23%)
Positive family history of AS	87 (15%)
Positive family history of AAU	7 (1%)
Positive family history of ReA	8 (1%)
Positive family history of IBD	12 (2%)
Positive family history of Psoriasis	36 (6%)
Total number of SpA-related diseases in first- or second-degree relatives
Number of patients with one disease	120 (20%)
Number of patients with two diseases	15 (3%)
Total number of family members with SpA-related diseases
Number of patients with one relative	102 (17%)
Number of patients with two relatives	30 (5%)
Number of patients with three relatives	3 (1%)
Total number of patients with positive family history in
First-degree relatives only	100 (17%)
Second-degree relatives only	25 (4%)
Both first- and second-degree relatives	10 (2%)
HLA-B27 positivity	310 (52%)
Elevated CRP/ESR	185 (31%)
Definite radiographic sacroiliitis^e	119/593 (20%)
Presence of active inflammation on MRI-SI	189/424 (45%)
Number of SpA features^f,g	2.4 (1.6)
Clinical diagnosis of axSpA^h	368 (62%)

Abbreviations: AAU Acute anterior uveitis, AS Ankylosing spondylitis, ASAS Assessment of SpondyloArthritis international Society, (ax)SpA (Axial) spondyloarthritis, CRP C-reactive protein, ESR Erythrocyte sedimentation rate, HLA-B27 Human leukocyte antigen B27, IBD Inflammatory bowel disease, IBP Inflammatory back pain, MRI-SI Magnetic resonance imaging of the sacroiliac joints, NSAID Nonsteroidal anti-inflammatory drug, ReA Reactive arthritis, SI Sacroiliac joint
Results are presented as mean ± SD unless specified otherwise
^a < 5% missing values
^b Self-reported ethnicity was missing for five patients, who are included in this category, and other self-reported ethnicities are black, East Indian, Hispanic/Latino, mixed, or Turkish
^c Back pain not present anymore or is much better 24–48 hours after a full dose of NSAID
^d Past or present condition
^e Grade ≥ 2 bilateral or grade ≥ 3 unilateral
^f Excluding HLA-B27 carriership and imaging
^g < 20% missing values
^h Level of confidence regarding the diagnosis is ≥ 6