The clinical differences between the ANCA phenotypes were reflected in their genetics: on the one hand, MPO-ANCA-positive EGPA was strongly associated with the HLA-DQ locus; on the other hand, ANCA-negative EGPA was found to be associated with BACH2, CDK6, GATA3, GPA33 and the IRF1/IL5 locus. This evidence concerns the gene IRF1 and eosinophilic granulomatosis with polyangiitis.