Table 1.

Summary of AS risk factors

Genetic

HLA-B27 [17–38]

MHC genes other than HLA-B27 [12, 18, 25, 28, 38–46]

ERAP1/2 [7, 25, 47–56]

SNPs within or adjacent to other genes (detailed in Table 3) [7, 11, 12, 40, 45, 47–70]

Gut microbiota and associated factors [71–74]

Altered gut microbiota, most notably a presence of [8, 75–79]:   • Lachnospiraceae   • Prevotellaceae   • Ruminococcaceae   • Rikenellaceae   • Porphyromonadaceae   • Bacteroidaceae

Lack of gut-induced protection by absence of breast feeding [80]

Infections

Klebsiella pneumoniae [81–87] (not established)

Respiratory tract infections and tonsillitis during childhood hospitalization [88]

Mechanical stress [89–93]

Gender at birth

Male [27, 94–102]

Social and lifestyle factors

Having older siblings [103]

Vitamin D deficiency [15, 104]

Smoking (including e-cigarettes) [105–108]

Other

Altered immune system and functionality [109–112]:   • Lower number of Tregs [111]   • Lower IL-10 production by CD4+ T cells but higher IL-6 production by CD8+ T cells [111]   • Increased MIF levels in serum and synovial fluid [112]

IL, interleukin; MIF, macrophage migration inhibitory factor; SNP, single-nucleotide polymorphism; Treg, regulatory T cell