A novel mutation at the JK locus causing Jknull phenotype in a Chinese family

Urea transporters are a group of proteins that facilitate urea movement across biological membranes. Kidd blood group (JK antigen) and urea transporter of human erythrocytes are carried by the same protein UT-B. To investigate the molecular basis of the Jknull phenotype in the Chinese population, blood samples from Chinese individuals were screened using the 2 mol/L urea solution hemolysis test. Urea and water permeability of erythrocytes membrane was measured by stopped-flow light scattering. Genomic DNA was extracted from lymphocytes. UT-B gene of Jknull’s family was analyzed using genomic PCR by primers designed to cover sequences of all exons and exon-intron boundaries in human UT-B gene. One Jknull subject was found from twenty thousand screened Chinese individuals, and it was confirmed that this individual did not express the erythrocyte urea transporter. Genomic sequence analysis of the Jknull individual showed that there were two point mutations, G→C, which is novel, and G→A, at the 3′-acceptor splice site (AG) of intron 5 of UT-B gene. Exon 6 is spliced out in the UT-B transcript due to either of these mutations. Water permeability in Jknull erythrocytes (Pf, ~0.00037 cm/s) was significantly lower than that in normal erythrocytes (Pf, ~0.00062 cm/s) after HgCl2 incubation, providing evidence for UT-B facilitated water transport in human erythrocytes.