Prevalence of RHD*DOL and RHCE*ce(818T) in two populations.

The alleles RHCEceBI (RHCEce 48C, 712G, 818T, 1132G) and RHCEceSM (RHCEce 48C, 712G, 818T) encode the low-prevalence Rh antigen STEM. These alleles frequently travel in cis with RHDDOL. To estimate the frequency of these alleles, we tested a total of more than 700 samples in two populations. Blood samples were obtained from patients with sickle cell disease and from blood donors of African descent. DNA extractions and analyses were performed by standard methods. In the United States, none of 70 patient samples had the RHCE818 nucleotide change. Two of 220 donors (frequency of 0.009) were heterozygous for RHCE818C/T (RHCEceBI). One of these samples had RHD/RHDDOL and the other had RHD/RHDDOL-2. In these 290 samples, no other RHDDOL alleles were found. In Brazil, 1 of 244 patients with sickle cell disease (frequency of 0.004) and 1 of 171 donors (frequency of 0.006) were heterozygous for RHCE818C/T (RHCEceBI). Testing of more than 500 additional samples from people of African descent, selected because they had a diverse range of common and variant RHCE alleles, did not reveal a sample with RHDDOL or RHD/RHDDOL-2 in the absence of RHCEce(818T). Although the numbers are small, our study shows that in the United States, the frequency of RHCE818T is 0.007 (2 in 290 samples) and in Brazil it is 0.004 (2 in 515 samples). The four RHCE818T alleles were RHCE*ceBI.