BLOOD GROUP GENOMICS
A DEL phenotype attributed to RHD Exon 9 sequence deletion:
slipped-strand mispairing and blood group polymorphisms
Genghis H. Lopez ,
Robyn M. Turner,
Eunike C. McGowan ,
Elizna M. Schoeman ,
Stacy A. Scott,
Helen O’Brien ,
Glenda M. Millard ,
Eileen V. Roulis ,
Amanda J. Allen,
Robert L. Flower ,
and Catherine A. Hyland
The RhD blood group antigen is
extremely polymorphic and the DEL phenotype
represents one such class of polymorphisms. The DEL
phenotype prevalent in East Asian populations arises
from a synonymous substitution defined as RHD*1227A.
However, initially, based on genomic and cDNA studies,
the genetic basis for a DEL phenotype in Taiwan was
attributed to a deletion of RHD Exon 9 that was never
verified at the genomic level by any other independent
group. Here we investigate the genetic basis for a
Caucasian donor with a DEL partial D phenotype and
compare the genomic findings to those initial molecular
STUDY DESIGN AND METHODS:
the RHD gene was amplified by long-range polymerase
chain reaction (PCR) for massively parallel sequencing.
Primers were designed to encompass a deletion, flanking
Exon 9, by standard PCR for Sanger sequencing.
Targeted sequencing of exons and flanking introns was
Genomic DNA exhibited a 1012-bp deletion
spanning from Intron 8, across Exon 9 into Intron 9. The
deletion breakpoints occurred between two 25-bp repeat
motifs flanking Exon 9 such that one repeat sequence
Deletion mutations bordered by repeat
sequences are a hallmark of slipped-strand mispairing
(SSM) event. We propose this genetic mechanism
generated the germline deletion in the Caucasian donor.
Extensive studies show that the RHD*1227A is the most
prevalent DEL allele in East Asian populations and may
have confounded the initial molecular studies. Review of
the literature revealed that the SSM model explains some
of the extreme polymorphisms observed in the clinically
significant RhD blood group antigen.
he RhD blood group antigen is clinically signifi-
cant and extremely polymorphic.
phenotype represents one such class of polymor-
phisms characterized by a quantitative reduction
in RhD antigen sites on red blood cells (RBCs).
RBCs phenotype as D– by standard serology and RhD
antigen is detected only after adsorbing and eluting anti-
D from these RBCs.
More than 40 RHD gene variants
associate with the DEL phenotype, the most prevalent
being the Asia-type DEL.
Such RBCs have been associ-
ated with primary and secondary immunization in D–
ABBREVIATIONS: SSM 5 slipped-strand mispairing; STR 5
short tandem repeat.
Research and Development,
Red Cell Reference
Medical Services, Clinical Services and
Research Division, Australian Red Cross Blood Service,
Brisbane, Queensland, Australia.
Address reprint requests to: Catherine A. Hyland, PhD,
MSc, Clinical Services and Research, Australian Red Cross
Blood Service, 44 Musk Avenue, Kelvin Grove, Brisbane,
Queensland 4059, Australia; e-mail: CHyland@redcrossblood.
This article was published online on 06 December 2017.
An error was subsequently identified. This notice is included in
the online versions to indicate that have been corrected 22 Jan-
The Australian government funds the Australian Red Cross
Blood Service for the provision of blood, blood products, and
services to the Australian community. This study has approval
from the Australian Red Cross Blood Service Human Research
Ethics Committee Application Number 2010#07.
Received for publication July 21, 2017; revision received
October 19, 2017; and accepted October 23, 2017.
Volume 58, March 2018 TRANSFUSION 685