Despite the identification of the high incidence red cell antigen Era nearly 40 years ago, the molecular background of this antigen, together with the other two members of the Er blood group collection, has yet to be elucidated. Whole exome and Sanger sequencing of individuals with serologically defined Er alloantibodies identified several missense mutations within the PIEZO1 gene, encoding amino acid substitutions within the extracellular domain of the Piezo1 mechanosensor ion channel. Confirmation of Piezo1 as the carrier molecule for the Er blood group antigens was demonstrated using immunoprecipitation, CRISPR/Cas9-mediated gene knockout and expression studies in an erythroblast cell line. We report the molecular bases of five Er blood group antigens: the recognised Era, Erb and Er3 antigens; and two novel high incidence Er antigens, described here as Er4 and Er5, establishing a new blood group system. Anti-Er4 and anti-Er5 are implicated in severe hemolytic disease of the fetus and newborn (HDFN). Demonstration of Piezo1, present at just a few hundred copies on the surface of the red blood cell, as the site of a new blood group system highlights the potential antigenicity of even low abundance membrane proteins and contributes to our understanding of the in vivo characteristics of this important and widely studied protein in transfusion biology and beyond.

Background: Currently, there is a shortage of an adequate supply of blood and blood products due to the unavailability of voluntary, non-remunerated donors from low-risk populations. Therefore, it is important to address the reasons for the unavailability of blood donors in order to increase recruitment.Aim: This study determined the level of knowledge and attitude in the wider Saudi Arabian population towards blood donation. Methods: A cross sectional study was conducted using an online questionnaire between Novembers 2021 and October 2022. Results: Of the 1506 individuals, only 17.9% were donors, of whom 11.2% had donated blood before. Through analysing the knowledge score, 81.9% of participants possessed knowledge regarding the necessity of screening a donation for infections and 90.5% positively confirmed that the HIV virus could be spread through the blood donation route, however, they were not familiar with other infections, such as syphilis. With regards to the levels of attitude, 74.2% of respondents strongly agreed on raising awareness of the importance of blood donation, whilst 54.2% strongly agreed that the availability of mobile blood donation centres would increase the level of donation drastically. Conclusions: Although the study showed that respondents were aware of certain factors regarding blood donation, there was an insufficiency of knowledge and attitudes regarding blood donation. This finding highlighted the need for identifying and addressing the defect of the knowledge that leads to an undesirable attitude towards blood donation.