STAT3 and rheumatoid arthritis: Comparison of the Y640F and D661Y STAT3 distribution of this new cohort of 108 healthy donor samples (99 individuals plus 9 from our study), to the 98 RA patients in our study showed a statistically different VAF distribution of STAT3 mutations in RA patients compared to HCs (Y640F mutation p=0.0005 and D661Y mutation p=0.0005, Pearson’s Chi-Squared test), with the majority of the difference stemming from mutations in the 0.008%-0.05% VAF range (Figure 3A).