TNFRSF21 and systemic lupus erythematosus: IKZF1 and IKZF3 mRNA and proteins are overexpressed in the cells of patients with SLE.4 5 7–10 Genetic variants in the IKZF1 and IKZF3 loci are associated with an increased risk of developing SLE.2 10 In particular, the IKZF1 polymorphism rs4917014 was identified as a trans-expression quantitative trait locus (eQTL) increasing expression of type I IFN response genes (HERC5, IFI6, IFIT1, MX1 and TNFRSF21).9