STAT4 and systemic lupus erythematosus: The only other study that has investigated a possible association in serum levels between the different genotypes of the STAT4 rs7574865 polymorphism was that performed by Hagberg et al. in 52 Swedish patients with SLE, in which it was observed that patients with the TT polymorphism genotype had higher levels of IFN-γ in plasma without a statistical difference.