In this study, we stratified 81 patients with RA and unexplained neutropenia or/and an increase in the number of LGLs into two groups (RA-associated T-LGLL or FS) based on the presence or absence of T-cell clonality; we then examined STAT3 and STAT5b gene mutations in both groups. This evidence concerns the gene STAT5B and rheumatoid arthritis.