Molecular basis of Cromer blood group antigens.

The Cromer blood group system consists of 10 antigens located on decay-accelerating factor (DAF). Previous molecular genetic analysis has determined the basis for four of these antigens. The present study was undertaken to identify the mutations that determine the remaining antigens. Existing or new data were used to localize each Cromer system antigen to a specific short consensus repeat (SCR) domain of DAF. The exon encoding that SCR domain was amplified by using the polymerase chain reaction (PCR) on genomic DNA obtained from individuals of that Cromer phenotype, and the DNA product was subjected to DNA sequence analysis. The Tc(a)/Tc(c) polymorphism is due to an R18P amino acid substitution in SCR1 of DAF. The Es(a+)/Es(a-) polymorphism is due to an I46N mutation in SCR1 of DAF. The WES(b)/WES(a) polymorphism is due to an L48R mutation in SCR1 of DAF. The UMC+/UMC- polymorphism is due to a T216M substitution in SCR4 of DAF. With information from previous reports and the findings of this study, the molecular genetic basis of all known alleles of the Cromer blood group system has been elucidated. Single amino acid substitutions are responsible for 9 of the 10 antigens (all except the multiple-epitope antigen IFC).