Isolation, characterization, and family study of DTI, a novel partial D phenotype affecting the fourth external loop of D polypeptides.
BACKGROUND
The Rh system is the most polymorphic of the blood group systems and is of major importance in transfusion medicine. The partial D phenotypes lack one or more of the D epitopes. These variants appear to have arisen through hybrid RhD-CE-D or by spontaneous point mutations in RhD. The serologic findings and the molecular characterization of a novel partial D phenotype, termed DTI, are presented here.


METHODS
RBCs from the DTI proband and RBCs from individuals with other partial D phenotypes were tested with MoAbs against 16 D epi- topes, according to the recommendations of the 4th ISBT Workshop on MoAbs (Rh Section 1A). A full-length cDNA encoding DTI and introns 4 and 5 of RhD were isolated and analyzed by DNA sequencing. A family study of the DTI allele was carried out using PCR-RFLP and long-range PCR methods.


RESULTS
Analysis of RBCs from the proband revealed that the DTI phenotype lacks epitopes D1, D2.1 (partial), D2.2, D5, D6 (partial), and D8. The DTI polypeptide exhibits seven amino acid substitutions in the D polypeptide: F223V, A226P, E233Q, V238M, V245L, G263R, and K267M. The genomic organization of DTI showed that the replacement of RhD with RhCE was located in intron 4, and the replacement of RhCE with RhD was located in intron 5. Family studies revealed that the DTI allele was inherited maternally, whereas the RhD- allele was inherited paternally in the proband.


CONCLUSIONS
The serologic data provide the first molecular characterization of DTI, a previously unknown partial D phenotype. This phenotype affected the D polypeptide within the fourth external loop, resulting in a new RhD-CE (entire exon 5)-D hybrid gene. It is worth noting that P226, encoded by exon 5, is derived from E of RhCE in the DTI polypeptide. Family studies demonstrated that DTI was associated with a cDTIE haplotype.
Omi
Toshinori
T
Department of Legal Medicine and Human Genetics, Jichi Medical School, Tochigi, Japan. t-omi@jichi.ac.jp
Takahashi
Junko
J
Seno
Taiko
T
Tanaka
Mitsunobu
M
Hirayama
Fumiya
F
Matsuo
Michie
M
Ueda
Naoki
N
Obara
Kenryo
K
Okuda
Hiroshi
H
Iwamoto
Sadahiko
S
Tani
Yoshihiko
Y
Kajii
Eiji
E
D000483:Alleles; D000911:Antibodies, Monoclonal; D001483:Base Sequence; D018076:DNA, Complementary / Q000097:blood; D000939:Epitopes / Q000097:blood / Q000737:chemistry / Q000276:immunology; D004912:Erythrocytes / Q000276:immunology; D005091:Exons; D005838:Genotype; D006801:Humans; D007438:Introns; D010375:Pedigree; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics; D010641:Phenotype; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D012204:Rh-Hr Blood-Group System / Q000235:genetics* / Q000276:immunology
D000911:Antibodies, Monoclonal; D018076:DNA, Complementary; D000939:Epitopes; D010446:Peptide Fragments; D012204:Rh-Hr Blood-Group System