An 18-year-old healthy female blood donor with Jk (a-b-) phenotype was detected in a routine survey by using the test for urea lysis resistance. Her red blood cells showed intermediate resistance between the ordinary Jk (a+b+) and the recessive Jk (a-b-) cells. Furthermore, the absorption-elution test on this proband's cells using anti Jka and anti Jkb sera demonstrated the presence of a weakly expressed Jka antigen. From these findings, we suspected a genetic mechanism different from that of the recessive Jk (a-b-), and carried out a family study. Of her 12 paternal blood relatives and sibs inclusively, ten were identified of their Kidd phenotype quite resembling to that of the proband, whereas her mother and other non-blood relatives showed a normal Kidd phenotype. This finding strongly suggests presence of a non-allelic dominant gene, which might inhibit the normal expression of Kidd antigens and result in a Jk (a-b-) phenotype, as was already proposed by Okubo et al (1986).
