A silenced allele in the Colton blood group system

K. Karpasitou, S. Frison, E. Longhi, F. Drago, R. Lopa, F. Truglio, M. Marini, S. Bresciani, M. Scalamogna, F. Poli

Research output: Contribution to journalArticlepeer-review


Background The antigens of the Colton blood group system, Co a and Co b, are encoded by a single gene that produces the aquaporin-1 (AQP1) protein, a water channel-forming protein, and are characterized by a single nucleotide polymorphism (SNP). A healthy Caucasoid blood donor originally typed as Co(a-b-) with commercial anti-Co b typed Co(a-b+) when retested with another anti-Co b. Retyped with two different molecular biology methods, the sample came out Co a/Co b. With the aim of understanding these discrepancies, serological, cytometric and molecular biology tests were carried out. Methods Absorption/elution studies with propositus red cells and controls were performed. The region spanning exon 1 to exon 4 of the Colton gene was sequenced, and flow cytometry analyses were carried out. Results Absorption/elution studies showed the absence of Co a and a weak expression of Co b. DNA sequencing confirmed a CT heterozygosity at nucleotide position 134 (i.e. Co a/Co b), and an additional heterozygous CT was found at position 112. The presence of the Co b allele that encodes for the Co b antigen was confirmed. The new allele has the base cytosine at nucleotide 134 (Co a), in cis with the new nucleotide 112T. The nucleotide substitution 112C>T causes a missense mutation leading to an amino acid change from proline (CCG) to serine (TCG) at codon 38. Conclusion The substitution found at codon 38 results in a modified AQP1 protein which explains the Co(a-b+) phenotype and possibly the weak expression of Co b.

Original languageEnglish
Pages (from-to)158-162
Number of pages5
JournalVox Sanguinis
Issue number2
Publication statusPublished - Aug 2010


  • Colton
  • null allele
  • red cell molecular typing

ASJC Scopus subject areas

  • Hematology


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