This ability of amino acid substitutions to explain the association of the MHC to PBC in a more parsimonious way than is achieved by classical HLA alleles contrasts with results previously found using stepwise regression in inflammatory bowel disease (IBD) [27], where classical HLA alleles (specifically HLA-DRB1*01:03) entered the model first and better explained the association than models based on amino acid substitutions, leading the investigators in that study to focus their subsequent efforts on an HLA-DRB1 centric model. The gene discussed is HLA-DRB1; the disease is inflammatory bowel disease.