Cromer blood group system consists of 12 high-prevalence and three low-prevalence antigens. The molecular basis for the antigens is known, and the majority is the product of a single nucleotide change in the DAF gene and has been localized to one of the four complement control protein domains on the DAF protein. Antibodies to Cromer antigens are rarely encountered. This case reports a 72 year-oldAfrican descendent Brazilian woman with endometrioid adenocarcionoma had an antibody reactive with all red blood cells (RBCs) and cord RBCs. The direct antiglobulin test (DAT) and autocontrol were negative. She had 2 previous pregnancies and a previous transfusion 20 years ago. Siblings were recruited and a familiar study was performed. Serological and molecular studies were carried out to define the patient‘s phenotype and the antibody specificity.

Serological investigation was performed by hemagglutination in gel cards.Antibody identification was performed in the patient's serum with untreated and treated RBCs with papain, trypsin, α-chymotrypsin and 200 mM dithiothreitol (DTT).Antigen typing was performed for the most common antigens with commercial reagents and for high frequency antigens with sera from our collection coming from SCARF. Genomic DNA was used to amplify and sequence CROM exons.

The patient‘s serum reacted with all panel cellsincluding phenotypically similar RBCs. Only the autologous control was non-reactive. Crossmatching was negative with RBCs of 2 siblings and positive with the other two. Antibody titration showed a titre of 64.The antigen was sensitive to papain, typsin and α-chymotrypsin-treatment but was resistant to 200 mM DTTwhich suggested the presence of a high-frequency antibody to an antigen of the Cromer system. Sequencing analysis of CROM revealed the patient and her two sisters with negative crossmatching were homozygous for the molecular change c.679G > Cin exon 6, which predict the Cr(a-) phenotype. DNA sequencing of the two other siblings with positive crossmatching showed this molecular change in heterozygous.The antibody was determined to be of anti-Cra specificity and other underlying antibodies were ruled out through adsorption and elution with R1R1, Jk(b-) and Fy(b-) allogeneic RBCs.

This study reported for the first time a rare case of anti-Cra in a Brazilian family. Due to the complexity of the Cromer system and the scarcity of anti-Cra and Cr(a-) RBCs, molecular analysis was essential for the conclusion of the case. Anti-Cra is rarely encountered and has already been related to moderate transfusion reaction but its clinical significance can be variable. Although no transfusions were requiredat this time, the family study was essential to find compatible donors.