RUNX1 and rheumatoid arthritis: Most interestingly, an association between functional variants of the OCTN1 gene and RA has been reported in the Japanese population leading to the hypothesis that the small nuclear polymorphism (SNP) in intron 1 of the OCTN1 gene lowers the affinity for the Runt-related transcription factor 1 (RUNX1), which regulates OCTN1 expression (Tokuhiro et al. 2003).