Two independent amino acid positions were identified after stepwise association analysis for amino acids in HLA-DRβ1, HLA-DQα1 and HLA-DQβ1 in the combined analysis. Two independent amino acid positions were identified after stepwise association analysis for amino acids in HLA-DRβ1, HLA-DQα1 and HLA-DQβ1 in the combined analysis. (A) Amino acid position 11 in HLA-DRβ1 showed the strongest association with LN (P<0.001). (B) Adjusting for position 11 in HLA-DRβ1, position 45 in HLA-DQβ1 was significantly associated with LN (P<0.001). (C) After adjusting for position 11 in HLA-DRβ1 and position 45 in HLA-DQβ1, no amino acid was significant (P>0.001). (D) Distribution of deviance improvement for all combinations of two amino acid positions. The model including position 11 in HLA-DRβ1 and position 45 in HLA-DQβ1 is the best fit model for LN. Ricong Xu et al. JASN 2017;28:3383-3394 ©2017 by American Society of Nephrology