Human leukocyte antigen association with azathioprine-induced drug hypersensitivity reactions in patients with anti-neutrophil cytoplasmic antibody associated vasculitis

Azathioprine (AZA) drug hypersensitivity reaction (DHR) is an uncommon yet potentially lethal condition that often goes unrecognised in patients with anti-Neutrophil Cytoplasmic Antibody (ANCA) associated vasculitis (AAV). We conducted a retrospective review of AAV patients on AZA maintenance therapy (N = 35). Participants were categorised into those who had experienced AZA-DHR (N = 15) and those who were AZA-tolerant (N = 20). Human leukocyte antigen (HLA) typing was performed in both groups. The primary endpoint was identification of a HLA gene association with AZA-DHR in the context of AAV. HLA-C*06:02, was solely expressed in AZA-DHR patients (33.3 %), whilst no patient who tolerated AZA carried this allele (0.0 %). This yielded a positive predictive value of 100 % for HLA-C*06:02 in predicting AZA-DHR in AAV patients, negative predictive value of 66.7 %, sensitivity of 33.3 % and specificity of 100 %. HLA-C*06:02 may predict the development of AZA-DHR in patients with AAV and inform safer therapeutic choice.