BLK and systemic lupus erythematosus: The shared genetic loci associated with RA and SLE are tumor necrosis factor receptor-associated factor (TRAF1), tumor necrosis factor receptor superfamily member 5 (CD40/TNFRSF5), TNF-α-induced protein 3 (TNFAIP3), interferon regulatory factor 5 (IRF5), B lymphoid tyrosine kinase (BLK).