Further evidence arguing against the possibility that the truncated form of ERα contributes to the attenuation of autoimmunity associated with the Esr1tm1Ksk allele comes from previous studies demonstrating that both the Esr1tm1Ksk allele as well as a second allele that represents a complete knockout of ERα (Esr1tm4.2Ksk) attenuate the development of lupus nephritis in females from the lupus-prone NZM2410 strain (44, 45). This evidence concerns the gene ESR1 and systemic lupus erythematosus.