Background: In 1994 during the investigation of a case of hemolytic disease of the newborn, a new low-incidence red cell (RBC) antigen, LOCR, was described. Although the presence of LOCR was associated with altered expression of Rh antigens, its formal assignment to the Rh blood group system did not occur until haplotype and linkage analysis conducted in 2003 provided the necessary proof. The current study was undertaken in an attempt to define the underlying RH mutation in LOCR+ individuals.
Study design and methods: Genomic DNA from five unrelated LOCR+ individuals and three Rh-matched control individuals was amplified by polymerase chain reaction with intronic primers flanking all 10 exons of RH. Amplified products were separated on 1 percent agarose gels and isolated for DNA sequence analysis in both the forward and the reverse directions.
Results: DNA sequence analysis of the three LOCR+ D- individuals revealed a single heterozygous 286G>A nucleotide substitution resulting in a predicted Gly>Ser substitution at amino acid 96. DNA sequence analysis from the two LOCR+ D+ individuals revealed the identical mutation, as well as all of the changes associated with the common RHD gene.
Conclusions: Based on our results, a Gly96Ser substitution in the Rhce polypeptide defines the low-incidence RBC antigen known as LOCR. This same amino acid change has previously been shown to be involved in the Rh:-26 phenotype, which suggests that LOCR and Rh26 are antithetical. Serologic investigations with various Rh:-26 cells and serum samples, however, reveal that only some c+ Rh:-26 phenotypes are LOCR+.