Distinctive Swann blood group genotypes: molecular investigations

Phenotypically, Sw(a+) erythrocytes have been classified as either 700:4,41 or 700:4,-41. Since anti-700.4, in particular, and sometimes anti-700.41 are contained in reagents defining other low-incidence antigens that are members of the Diego blood group system, we undertook the current investigation in an attempt to establish whether or not Swann antigens are also Diego system members.

DNA from the members of three unrelated kindreds whose red cells type as Sw(a+) was isolated and analyzed for variation in SLC4A1 (solute carrier family, anion exchanger member 1 gene) by single-strand conformational polymorphism (SSCP) and DNA sequence analyses.

Polymerase chain reaction-amplified exon 16 SLC4A1 products from the DNA of all Sw(a+) individuals displayed a mobility shift by SSCP. A similar mobility shift was not observed in the DNA from Sw(a-) family members or in the amplified DNA from control individuals. DNA sequencing revealed different mutations, CGG-->CAG and CGG-->TGG, that result in Arg646Gln and Arg646Trp substitutions in erythroid protein band 3, respectively.

Through genotypic analyses, we have characterized two point mutations related to the Swann blood group. The possible relationship between the resultant amino acid substitutions and the expression of Swann antigens has been discussed.