Molecular genetic analysis of the Kidd blood group system in a Taiwanese family with Jk_null phenotype

Two common polymorphisms of 588G/A and 838G/A have been demonstrated in the JK gene, and the latter defines the Jk^a/Jk^b phenotypes. The Jk_null phenotype has been characterized as the absence of Jk^a and Jk^b antigen expression on red cells. We performed a molecular analysis of a family with the Jk_null phenotype and subsequently demonstrated the presence of different JK cDNA haplotypes. In the study, three members of a Jk_null family and 48 randomly-selected individuals were enrolled. The coding exons of the JK gene of the Jk_null family members were amplified by polymerase chain reaction (PCR), and the sequences were analyzed. The genomic region encompassing exons 7~9 of the JK gene was PCR-amplified, cloned, and sequence-determined to elucidate the JK haplotype. We demonstrated that 3 missense mutations, 222C>A, 499A>G and 896G>A were in the JK genes of the Jk_null family members, in addition to the known IVS5–1g>a splice site mutation. Analysis of 48 randomly-selected individuals showed that 499A>G was a common polymorphism, besides 2 Jk_null alleles with respective mutation of 222C>A and 896G>A being demonstrated in the Jk_null family. After compiling the nucleotide information of the polymorphic 499, 588, and 838 positions from the randomly-selected individuals, 5 JK cDNA haplotypes, constituted by the 3 polymorphic sites, were demonstrated. Among these, the JK^a1 (499A, 588G and 838G; 46.9%),JK^b1 (499A, 588G and 838A; 23.9%), and JK^b2(499G, 588G and 838A; 21.9%) were found as the 3 major haplotypes in the Taiwanese population. In conclusion, the Jk_null phenotypes with respective mutations of 222C>A, 896G>A and IVS5–1g>a, were identified in a Taiwanese family. The existence of 5 JK cDNA haplotypes with the 499A/G polymorphism was also demonstrated in the Taiwanese population.