TRIM21 and systemic lupus erythematosus: Interestingly, the striking difference in the phenotype of 2 Ro52/Trim21-KO mice, in which one develops lupus-like disease and the other has a normal life span (2, 9), has been attributed to the potential production of a truncated Ro52 protein that is overexpressed in the mouse that develops lupus (32, 33).