Genomic characterization of the Kidd blood group gene: different molecular basis of the Jk(a-b-) phenotype in Polynesians and Finns

BACKGROUND: The clinically important Kidd (JK) blood group antigens are carried by the urea transporter in red cells. The rare Jk(a-b-) phenotype can be caused by homozygosity at the JK locus for a silent allele, Jk. This phenotype has been recorded in many ethnic groups, but it is most abundant among people originating from the Polynesian Islands and Finland. The molecular basis for Jk(a-b-) is unknown in these populations. STUDY DESIGN AND METHODS: Blood samples from individuals of Swedish, Polynesian, and Finnish origin were collected and characterized by routine JK blood group serology and JK genotyping. Genomic DNA covering the exons and intervening introns of the JK gene coding region was amplified by polymerase chain reaction, and fragments were directly sequenced. RESULTS: Exon and partial intron sequences in the coding region of the JK gene were determined. Finnish and Polynesian Jk alleles were analyzed; the only deviations from consensus were a splice-site mutation (G-->A) in Polynesians, causing skipping of exon 6, and a T871C substitution predicted to disrupt a potential N-glyco-sylation motif (NSS-->NSP) in Finns. Methods for rapid detection of silent Jk alleles were developed for clinical application. CONCLUSION: Polynesians and Finns have two different molecular alterations in their Jk alleles, both of which can now be determined by polymerase chain reaction.