ORIGINAL RESEARCH Molecular basis of weak D expression in the Indian population and report of a novel, predominant variant RHD allele Yann Fichou , 1,2 Disha Parchure, 3 Harita Gogri, 3 Vidya Gopalkrishnan, 3 C edric Le Mar echal, 1,2,4,5 Jian-Min Chen, 1,2 Claude F erec, 1,2,4,5 Manisha Madkaikar, 3 Kanjaksha Ghosh, 3 and Swati Kulkarni 3 BACKGROUND: The Rh blood group system is the most polymorphic system and is implicated in hemolytic transfusion reaction and hemolytic disease of the fetus and newborn. Molecular genetics of the RH genes have been extensively studied in Caucasians, Africans, and East Asians and the variant alleles giving rise to weak and partial D phenotypes have been reported. However, limited genetic studies have been carried out in the large Indian population, even though the variability of Rh expression has been documented. STUDY DESIGN AND METHODS: In this study we sought to characterize the molecular bases of weak D expression in Indians. RHD gene in samples presenting with a weak D phenotype by serologic analyses (n 5 223) was genotyped by conventional molecular approaches. RESULTS: In addition to referenced and novel single- nucleotide variations, a novel approximately 12-kb duplication event, including Exon 3, was identified predominantly in variant D samples (130/223, 58.3%) and characterized at the nucleotide sequence level. Functional analyses suggested that this genetic variation quantitatively affects the expression of the normal transcript and then subsequently the expression of the normal RhD protein. CONCLUSION: We describe a major novel, variant RHD allele in Indians that can be easily identified routinely by implementing a simple genotyping assay. Although we may consider this variation as a weak partial D variant, further studies and observations are needed to confirm the same. These findings may contribute to improve significantly Rh blood group diagnostics in more than one billion Indians. A mong the 36 blood group systems officially acknowledged by the International Society of Blood Transfusion (ISBT, www.isbtweb.org/fil- eadmin/user_upload/Working_parties/WP_on_ Red_Cell_Immunogenetics_and/Updates/Table_of_blood_ group_systems_v5_0_151215.pdf), the Rh blood group ABBREVIATION: CNV(s) 5 copy number variation(s). From the 1 Etablissement Franc ¸ais du Sang (EFS)–Bretagne; and the 2 Institut National de la Sant e et de la Recherche M edicale (Inserm), UMR1078, Brest, France; the 3 National Institute of Immunohaematology (NIIH), Indian Council of Medical Research (ICMR), KEM Hospital Campus, Parel, Mumbai, India; and the 4 Laboratoire de G en etique Mol eculaire et d’Histocompatibilit e, Centre Hospitalier R egional Universitaire (CHRU), H^ opital Morvan; and the 5 Facult e de M edecine et des Sciences de la Sant e, Universit e de Bretagne Occidentale, Brest, France. Address reprint requests to: Swati S. Kulkarni, PhD, National Institute of Immunohaematology, Indian Council of Medical Research (NIIH-ICMR), 13th Floor, NMS Building, KEM Hospital Campus, Parel, Mumbai 400 012, India; e-mail: swatiskulkarni@gmail.com. or Yann Fichou, PhD, EFS–Bre- tagne, Inserm UMR1078, 46 rue F elix Le Dantec, CS 51819, 29218 Brest, France; e-mail: Yann.Fichou@efs.sante.fr. This work was supported by the Indo-French Centre for the Promotion of Advanced Research/Centre Franco-Indien pour la Promotion de la Recherche Avanc ee (IFCPAR/CEFIPRA, Project 5203-1), the Indian Council of Medical Research (ICMR), the National Institute of Immunohaematology (NIIH), the Etablissement Franc ¸ais du Sang (EFS)–Bretagne, the EFS– Direction de la Recherche, de la Valorisation et de l’Innovation (La Plaine-St-Denis, France), and the Institut National de la Sant e et de la Recherche M edicale (Inserm). Received for publication August 7, 2017; revision received January 22, 2018; and accepted January 23, 2018. doi:10.1111/trf.14552 V C 2018 AABB TRANSFUSION 2018;00;00–00 Volume 00, February 2018 TRANSFUSION 1