HLA-DQB1 and Achalasia: In addition, two amino acid substitutions in the extracellular domain of HLA-DQα1 at position 41 (lysine encoded by HLA-DQA1∗01:03) and of HLA-DQβ1 at position 45 (glutamic acid encoded by HLA-DQB1∗03:01 and HLA-DQB1∗03:04) independently confer achalasia risk [29].