Outliers in RhD membrane integration are explained by variant RH haplotypes.
BACKGROUND
Variations in a multipass transmembrane protein may affect its membrane integration. To study this effect, the systematic molecular characterization of variant D antigen density is a suitable model. Unlike most other membrane proteins, the expression of the D antigen is often determined by a single allele, because it occurs frequently in hemizygous form.


METHODS
The D antigen density distribution of 530 CcDee, 475 ccDEe, and 514 ccDee random samples was established by flow cytometry. The molecular bases of samples with D antigen densities outside a bell-shaped peak was investigated.


RESULTS
The antigen densities of 499 CcDee, 437 ccDEe, and 480 ccDee samples formed bell-shaped peaks. Three, 10, and 12 samples, respectively, had decreased antigen densities and carried variant RHD alleles. Weak D type 19, RHD(I204T); weak D type 20, RHD(F417S); and the partial D DYU (also known as DQC), RHD(R234W) were new RHD alleles. Twenty-eight CcDee, 28 ccDEe, and 22 ccDee samples had increased antigen densities; 53 of them lacked a hybrid Rhesus box and were thus predicted to be RHD homozygous. Eight ccDee samples were predicted to be heterozygous despite a large relative dose of RHD to RHCE alleles in quantitative polymerase chain reaction. One of these samples was further investigated and carried an RHD-CE hybrid transcript characteristic for a -D- haplotype.


CONCLUSIONS
Unusual little and large RhD protein integration into the membrane could be traced to a host of distinct protein variants. Weak expression of D antigen was invariably associated with variant RHD alleles. Larger than normal D antigen density may often be caused by the presence of two D encoding alleles, which may be located in cis, and confounding zygosity testing that is solely based on gene copy number.
Yu
Xinjian
X
Department of Transfusion Medicine, University Hospital, and the Institute for Clinical Transfusion Medicine and Immunogenetics, Ulm, Germany.
Wagner
Franz F
FF
Witter
Bernd
B
Flegel
Willy A
WA
D000483:Alleles; D002462:Cell Membrane / Q000235:genetics / Q000276:immunology; D005260:Female; D005434:Flow Cytometry; D018628:Gene Dosage / Q000235:genetics* / Q000276:immunology; D005786:Gene Expression Regulation / Q000235:genetics* / Q000276:immunology; D006239:Haplotypes / Q000235:genetics / Q000276:immunology; D006579:Heterozygote; D006801:Humans; D008297:Male; D008954:Models, Biological; D012204:Rh-Hr Blood-Group System / Q000235:genetics* / Q000276:immunology
D012204:Rh-Hr Blood-Group System; C026410:Rho(D) antigen