Background/PurposeFirst-degree relatives (FDRs) of patients with ankylosing spondylitis (AS) may be at high risk of spondyloarthritis. We examined the frequency, characteristics of chronic back pain (CBP), associated features, persistence of symptoms, and HLA-B27 allele frequency in FDRs of AS patients, also comparing those FDRs with participants in NHANES 2009–2010 with CBP.Methods399 FDRs of AS probands were divided into: (1) No CBP (subjects >40 years old at study visit without CBP) (n=162); (2) NICBP (non-inflammatory CBP) (n=82), and (3) CIBP (inflammatory CBP) (n=155). White FDRs with CBP were compared with 772 participants in NHANES 2009–2010 with CBP. FDRs were invited to return for reassessment.ResultsFDRs with CIBP had earlier onset of CBP than those with NICBP (p<0.001) and had higher frequency of heel pain than those without CBP (p=0.002). HLA-B27 occurred in 57% of FDRs with CIBP vs 39.6% of those without CBP (p=0.005, OR=1.9). Of 23 patients with CIBP at baseline re-evaluated 67.04±31.02 months later, 16 (73%) still had CIBP, whereas 4 (31%) of 13 NICBP patients seen 61.23±31.84 months later remained symptomatic.ConclusionCIBP in FDRs of AS patients is HLA-B27-associated, has earlier onset and tends to persist compared to NICBP.