Collectively, these findings indicate that FMF-SpA coexistence defines a distinct clinical and genetic entity characterized by balanced sex distribution, lower HLA-B27 frequency compared to classic SpA, and a strong link between HLA-B27 positivity and amyloidosis risk, underscoring a complex genetic interaction between MEFV variants and HLA-B27 in disease expression. This evidence concerns the gene MEFV and amyloidosis.