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Molecular basis of the Dombrock null phenotype
M Rios1, K Hue-Roye, J R Storry
1Immunochemistry Laboratory, New York Blood Center, New York, New York 10021, USA. maria_rios@nybc.org
Background:
The Dombrock blood group system consists of two antithetical antigens, Do(a) and Do(b), and three high-incidence antigens, Gregory (Gy(a)), Holley (Hy), and Joseph (Jo(a)). The null phenotype of the Dombrock blood group system (Do(null)) was identified when it was found that Gy(a-) RBCs also lack Do(a), Do(b), Hy, and Jo(a).
Study Design And Methods:
DNA from three Gy(a-) persons was analyzed. PCR products for each of the three DO exons and their flanking intronic regions were sequenced in both directions. The cDNA from two of the people was subjected to PCR using primers in exon 1 and exon 3, and the products were sequenced.
Results:
The Do(null) phenotype is associated with a single nucleotide mutation in the acceptor splice site of DO (IVS1-2a>g), which results in outsplicing of exon 2.
Conclusion:
Outsplicing of exon 2 is predicted to cause a -1 frameshift and a premature stop codon. Any product of such a transcript would lack the glycosyl-phosphatidylinositol-anchor motif, and RBCs would be devoid of the Do glycoprotein.