ESR1 and systemic lupus erythematosus: Thebiology of these differences has been explored: one explanation is the number ofX chromosomes and genetic variants on the X chromosome (66, –68);another important etiological explanation is the role of estrogen in SLE.Estrogen's primary effects are mediated by transcription activity of theintracellular estrogen receptors, which profile is altered in T-cells fromfemale SLE patients (69,70).