Table 1.

AxSpAs: key genetic features

axSpAs	HLA-B27 association	Other HLA-associations	Non-MHC associations
			IL23R	ERAP1	ERAP2	MEFV
AS	89% [1]	Risk: B40, B47, B51, A2, DRB1*0103 Protective: B7, B57 [2]	Yes [3]	Yes [3]	Yes [3]	Yes [4]
nr-axSpA	Radiographic arm 58% [5]	Unknown	Unknown	Unknown	Unknown	Unknown
Psoriasisa	No	C*0602, C*1203 [6]	Yes [7, 8]	Yes [9]	Yes [9]	Unknown
PsA	64% (axial disease) [10]	C*0602, A2, B38, B39 [6]	Yes [11]	Yes [12]	Probable [13]	Probable [14]
IBD-associated SpA	41% (axial disease) [15]	Unknown	Yesb	Nob	Yesb	Probable [16]b
Reactive arthritis	16–80% [17]	Unknown	Unknown	Unknown	Unknown	Unknown
Sarcoidosis arthritis	Unclear	DQ2-DR3 [18]	Unknown	Unknown	Unknown	Unclear
Behçet’s disease	No	B51 [19]	Yes [20]	Yes [20]	No [21]	Probable [22]
FMF	Unknown	Unknown	Unknown	Unknown	Unknown	Yes [23]

^aIncluded as a comparator for PsA, although not an axSpA.

^bIBD overall, not restricted to those with arthritis.

Probable means P >0.05–<10^–5. Unclear means contradictory studies exist.