A comprehensive study of rare Rhesus phenotype case

Abstract

Introduction. The RH system includes major antigens D, C/c and E/e encoded by two closely related RHD and RHCE genes. Correct identifi cation of Rh antigens in both donors and recipients is the key to proper transfusion practice. However, there are cases when Rh antigens cannot be detected by standard serological typing. For example, –D– phenotype has no expression of C, c, E, and e antigens on the surface of erythrocytes due to various genetic rearrangements in the RHCE gene.Aim: to present a study of a family where two siblings have a defi cient -D-phenotype with a normal rhesus phenotype in the parentsMaterials and methods. A comprehensive study of family N., including parents and two sons was conducted. Initially, an unusual phenotype -D- was identifi ed in the siblings, who are currently donors. All family members identifi ed themselves as Tatars. Serology tests were performed using gel cards. Genomic DNA of family members, as well as cDNA of siblings, was examined by allele-specifi c PCR, exon-scanning assay, and Sanger sequencing. In addition, copy number analysis was performed to identify rearrangements in the RHD and RHCE genes.Results. During serological typing of siblings, only the D antigen was revealed, while the C/c and E/e antigens were absent. Molecular genetic analysis suggested that the cause of the phenotype –D– in the brothers was a hybrid allele RHCE-D(3-8)- CE in homozygous status, forming a haplotype inherited from each parent with the normal RHD allele. The sequence of the fi rst two exons in the hybrid allele corresponded to RHCE*C allele. The parents were heterozygous for the identifi ed allele, so the expression of C/c and E/e antigens was not altered.Conclusion. Two donors with the –D– phenotype were assessed by comprehensive study. Identifi cation of the genetic causes of such variants in recipients is necessary to ensure safety during transfusion of erythrocyte-containing blood components. Genotyping of donors with Rh-defi cient phenotypes is also highly recommended in order to predict the molecular structure of Rh antigens.