Although it is unclear how impaired expression of Lbr would facilitate the development of IgM autoantibodies recognizing calreticulin, the presence of anti-calreticulin autoantibodies has been described in SLE patients (Kishore et al., 1997; Sanchez et al., 2000), and is associated with increased risk of fetal heart conduction block (Orth et al., 1996; Suzuki et al., 2005). Here, LBR is linked to systemic lupus erythematosus.