A new low-frequency red cell antigen, 'SARAH'

International society of blood transfusion working party on red cell immunogenetics and terminology: report of the Seoul and London meetings

The Working Party has met twice since the last report: in Seoul, South Korea 2014, and in London, UK 2015, both in association with the International Society of Blood Transfusion (ISBT) Congress. As in previous meetings, matters pertaining to blood group antigen nomenclature were discussed. Eleven new blood group antigens were added to seven blood group systems. This brings the current total of blood group antigens recognized by the ISBT to 346, of which 308 are clustered within 36 blood groups systems. The remaining 38 antigens are currently unassigned to a known blood group system.

SARA: a "new" low-frequency MNS antigen (MNS47) provides further evidence of the extreme diversity of the MNS blood group system

BACKGROUND

Until recently, SARAH (SARA) was a low-frequency antigen within the 700 series (700.052). SARA was discovered in Australia and subsequently described in Canada where anti-SARA was implicated in severe hemolytic disease of the fetus and newborn (HDFN). This study investigated whether SARA could be recategorized into an existing, or novel, blood group system.

STUDY DESIGN AND METHODS

Serologically typed Australian SARA family members (n = 9) were exome sequenced followed by bioinformatics analysis. Sanger sequencing of Exon 3 of GYPA of Australian (n = 9) and Canadian (n = 9) family members was then performed, as were peptide inhibition studies.

RESULTS

Exome sequencing identified 499,329 single-nucleotide variants (SNVs) within the nine individuals. Filtering excluded SNVs with an NCBI dbSNP ID (n = 482,177) and non-protein coding SNVs (n = 14,008); for the remaining 3144 SNVs, only one, c.240G>T of GYPA encoding p.Arg80Ser, was present in all six SARA-positive individuals. Sanger sequencing confirmed the presence of c.240G>T in the Australian SARA-positive individuals and demonstrated the same genetic basis in the Canadian SARA family. For a peptide representing the SARA sequence, inhibition of anti-SARA against SARA-positive cells was 84.6% at a concentration of 1.0 mg/mL.

CONCLUSION

We provide evidence that the SARA antigen is encoded by a SNV on GYPA and SARA has been reassigned to the MNS blood group system, now MNS47. This discovery provides a basis for application of genetic approaches in SARA typing when clinically indicated, for example, in HDFN.

Approaches to determination of a full profile of blood group genotypes: single nucleotide variant mapping and massively parallel sequencing

The number of blood group systems, currently 35, has increased in the recent years as genetic variations defining red cell antigens continue to be discovered. At present, 44 genes and 1568 alleles have been defined as encoding antigens within the 35 blood group systems. This paper provides a brief overview of two genetic technologies: single nucleotide variant (SNV) mapping by DNA microarray and massively parallel sequencing, with respect to blood group genotyping. The most frequent genetic change associated with blood group antigens are SNVs. To predict blood group antigen phenotypes, SNV mapping which involves highly multiplexed genotyping, can be performed on commercial microarray platforms. Microarrays detect only known SNVs, therefore, to type rare or novel alleles not represented in the array, further Sanger sequencing of the region is often required to resolve genotype. An example discussed in this article is the identification of rare and novel RHD alleles in the Australian population. Massively parallel sequencing, also known as next generation sequencing, has a high-throughput capacity and maps all points of variation from a reference sequence, allowing for identification of novel SNVs. Examples of the application of this technology to resolve the genetic basis of orphan blood group antigens are presented here. Overall, the determination of a full profile of blood group SNVs, in addition to serological phenotyping, provides a basis for provision of compatible blood thus offering improved transfusion safety.

Hemolytic disease of the fetus and newborn caused by an antibody to a low-prevalence antigen, anti-SARA

BACKGROUND

The first case describing the SARAH (SARA) antigen occurred in 1990, in an Australian blood donor. Hemolytic disease of the fetus and newborn (HDFN) due to anti-SARA has not been previously described.

CASE REPORT

We report a case of HDFN in a multiparous female. The pregnancy was unremarkable except that she was involved in a seemingly minor motor vehicle accident at 25 weeks' gestation. Routine prenatal antibody screening was negative throughout the pregnancy. She presented at 37 weeks' gestation because of decreased fetal movements. Labor was induced and a 2702-g infant male was delivered. The infant's hemoglobin was 49 g/L and the bilirubin was 153 µmol/L.

RESULTS

Blood samples from the parents and infant were referred to Canadian Blood Services National Immunohematology Reference Laboratory and subsequently to the Australian Red Cross Red Cell Reference Service. The father's and infant's red blood cells were confirmed to be SARA positive, and the mother's plasma contained anti-SARA.

CONCLUSION

The infant was successfully treated with a double-volume exchange transfusion. This is the first example of HDFN associated with this antibody.