However, the role of IHH in SpA has not been widely evaluated so far and only one study analyzed the serum levels of IHH of patients with AS, RA, and healthy subjects, and the effect of such serum on chondrocyte cell cultures, finding higher levels of IHH in patients with AS in comparison with AR patients, as well as in AS patients treated with TNFi compared to those not receiving therapy [226]. This evidence concerns the gene IHH and rheumatoid arthritis.