Moreover, these differences were high between RA + functional disability compared to RA + preserved physical function; thirdly, our study identified several variables correlating with serum follistatin levels and HAQ-DI; finally, we reported the anthropometric, functional, and clinical characteristics of RA + functional disability compared to RA + preserved physical function, using an HAQ-DI cutoff value of ≥0.6. This evidence concerns the gene FST and rheumatoid arthritis.