Background:The Kidd (JK) blood group system is clinically important intransfusion medicine. Alloantibodies to antigens in this system may be produced following blood transfusion or during pregnancy and can result in serious hemolytic transfusion reactions and hemolytic disease of the newborn (HDN). The two major codominant alleles of the JK gene, Jka and Jkb, have a similar frequency in Caucasian populations (0.51 and 0.49, respectively) and define 3 common phenotypes Jk(a+b+), Jk(a+b-), Jk(a-b+), while frequency of Jk(a-b-) or Jknull phenotype is exceedingly rare. Many individuals of Polynesian extraction have been identified as Jknull. Its frequency and molecular characterization for Chinese people in Taiwan, however, has not yet been clarified.

Study design and methods: By using the lately developed single-tube allele-specific primer/multiplex PCR technique, a total of 320 random whole blood samples were analyzed. In addition, three samples already serologically proven as Jknull phenotype in our Lab were also investigated.

Results: None of the 320 random whole blood samples was serologically typed as Jk(a-b-), while the frequencies of three other phenotypes were 47.5% for Jk(a+b+), 23.1% for Jk(a+b-), and 29.4% for Jk(a-b+). Interestingly, two Jka/Jk and four Jkb/Jk were identified, resulting in a gene frequency of Jka - 46.72%, Jkb - 52.34% and silent Jk - 0.94%. As for the three samples of Jknull phenotype all belonged to the so-called Polynesian type, i.e.3′-acceptor splice site G->A mutation of intron 5 that resulted in the skipping of exon 6 (called mutation JKΔ6).

Conclusion: The present study confirms that the single-tube allele-specific primer/multiplex PCR technique has enabled genomic typing of the Kidd blood group easier and reliable. The frequency and molecular characterization of JK phenotypes for Chinese people in Taiwan have been clearly characterized.

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