May the FORS be with you: a system sequel

Abstract

This article is an update of the review of the FORS system published in Immunohematology in 2017 (Hult AK, Olsson ML. The FORS awakens: review of a blood group system reborn. Immunohematology 2017;33:64-72). This update incorporates the most recently presented knowledge on this still enigmatic system and its genetic, enzymatic, and immunological aspects. Further insight into the genetic variation and allele frequencies of the GBGT1 locus has been reported, and screening studies regarding the prevalence of naturally occurring anti-FORS1 in human plasma have been performed and presented. More basic knowledge on the specificity of the gene product, the Forssman synthase, has been obtained in several detailed studies, and its relation to the homologous ABO gene has been investigated. Taken together, we summarize recently added information about the carbohydrate-based FORS blood group system (International Society of Blood Transfusion number 031).

ABO blood group antigens and differential glycan expression: Perspective on the evolution of common human enzyme deficiencies

“…Anti-FORS1 antibodies are usually naturally occurring and mainly IgM ( Cohn et al., 2020 ; Hult and Olsson, 2017 ). Because these antibodies are rare, their clinical significance is not well known, but they may cause intravascular hemolysis ( Hult and Olsson, 2020 ).…”

The Usefulness of Rare Blood Group Systems in the Risk Determination for Severe COVID-19

“…In place of FS, humans produce the natural anti-Forssman antibody, which activates the complement system when interacting with the FS Ag. These can hemolyze FORS1+ erythrocytes in a complement dependent manner in vitro [ 29 , 30 ].…”