Victor E. Ortega, Nadia N. Hansel, Dara G. Torgerson, Dan L. Nicolae, Candelaria Vergara, Emiko Noguchi, Monica Campbell, Meher Preethi Boorgula, Terri H. Beaty, James G. Wilson, Wataru Morii, Deborah A. Meyers, Carole Ober, Jean G. Ford, Sophie Limou, Leslie A. Lange, Alexandre Walencik, Margaret A. Taub, Estelle Geffard, Mezbah U. Faruque, Kathleen C. Barnes, Ingo Ruczinski, Sameer Chavan, Rasika A. Mathias, Michelle Daya, Eugene R. Bleecker, Nicolas Vince, Harold Watson, Nicholas Rafaels, Venceslas Douillard, Pierre-Antoine Gourraud, Centre de Recherche en Transplantation et Immunologie (U1064 Inserm - CRTI), Institut National de la Santé et de la Recherche Médicale (INSERM)-Université de Nantes - UFR de Médecine et des Techniques Médicales (UFR MEDECINE), Université de Nantes (UN)-Université de Nantes (UN), Department of Medicine [Aurora, CO, USA], University of Colorado [Denver], Université de Tsukuba = University of Tsukuba, Johns Hopkins University (JHU), Wake Forest School of Medicine [Winston-Salem], Wake Forest Baptist Medical Center, University of Mississippi Medical Center (UMMC), The University of the West Indies, Titu Maiorescu University Bucharest, Titu Maiorescu University = Universitatea Titu Maiorescu [Buchares] (UTM), Center for Human Genomics, Wake Forest University, Einstein Medical Center [Philadelphia, PA, USA], Howard University College of Medicine [Washington, DC, USA], University of Arizona, University of Illinois [Chicago] (UIC), University of Illinois System, University of California [San Francisco] (UCSF), University of California, European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No.846520., University of California [San Francisco] (UC San Francisco), University of California (UC), and CCSD, Accord Elsevier
Background Asthma is a complex chronic inflammatory disease of the airways. Association studies between HLA and asthma were first reported in the 1970s, and yet, the precise role of HLA alleles in asthma is not fully understood. Numerous genome-wide association studies were recently conducted on asthma, but were always limited to simple genetic markers (single nucleotide polymorphisms) and not complex HLA gene polymorphisms (alleles/haplotypes), therefore not capturing the biological relevance of this complex locus for asthma pathogenesis. Objective To run the first HLA-centric association study with asthma and specific asthma-related phenotypes in a large cohort of African-ancestry individuals. Methods We collected high-density genomics data for the Consortium on Asthma among African-ancestry Populations in the Americas (N = 4993) participants. Using computer-intensive machine-learning attribute bagging methods to infer HLA alleles, and Easy-HLA to infer HLA 5-gene haplotypes, we conducted a high-throughput HLA-centric association study of asthma susceptibility and total serum IgE (tIgE) levels in subjects with and without asthma. Results Among the 1607 individuals with asthma, 972 had available tIgE levels, with a mean tIgE level of 198.7 IU/mL. We could not identify any association with asthma susceptibility. However, we showed that HLA-DRB1∗09:01 was associated with increased tIgE levels (P = 8.5 × 10−4; weighted effect size, 0.51 [0.15-0.87]). Conclusions We identified for the first time an HLA allele associated with tIgE levels in African-ancestry individuals with asthma. Our report emphasizes that by leveraging powerful computational machine-learning methods, specific/extreme phenotypes, and population diversity, we can explore HLA gene polymorphisms in depth and reveal the full extent of complex disease associations.