The ancestral haplotype AH8.1 (also known as MHC 8.1) is a multigene haplotype consisting of HLA-A*01:01 -B*08:01- C*07:01 -DRB1*03:01 -DQA1*05:01 -DQB1*02:01. Genes from AH8.1 or the complete haplotype have been associated with risk or severity of disease in a number of inflammatory and autoimmune conditions including autoimmune hepatitis, myasthenia gravis, systemic lupus erythematosus, type 1 diabetes, a range of myositis phenotypes and Crohn’s disease (Lee et al., 2017; Price et al., 1999; Manabe et al., 1993; Miller et al., 2015; Gorodezky et al., 2006). The gene discussed is HLA-A; the disease is Crohn disease.