The <i>BTN2A1</i> <sub>rs1977199A</sub> allele was protective in RA (OR = 0.93) but increased r-axSpA risk (OR = 1.23), and was associated with reduced IL22 (p = 0.00016) and elevated HO-1 in obese individuals (p = 6.73×10<sup>-6</sup>). Here, HMOX1 is linked to rheumatoid arthritis.