MTHFR and rheumatoid arthritis: To date, there has been no report on the correlation between MTHFR 1298A>C and effusion in hemophilia or rheumatoid arthritis/inflammatory arthropathy; the observed effect of the two MTHFR variants should be validated in cohort studies, where patients are stratified by hemophilia severity and hemophilia causative variations in F8 or F9.