Background: Although antibodies to Js(a) and Js(b) are clinically significant, reagent-quality anti-Js(a) and anti-Js(b) are not readily available. A sequence-specific primer-polymerase chain reaction (SSP-PCR) genotyping assay was tested that makes use of two single-nucleotide polymorphisms (SNPs) at positions 1910 and 2019 of KEL. These SNPs distinguish the gene encoding Js(a), KEL6; and Js(b), KEL7.
Study design and methods: Four primer sets that selectively amplified KEL6 and KEL7 from genomic DNA were developed. Two sets detected the SNP at bp 1910 and two sets detected the bp 2019 SNP. KEL6 and KEL7 genotyping and Js(a) and Js(b) phenotyping results were compared among 64 subjects.
Results: The SSP-PCRs were specific for KEL6 and KEL7 when testing DNA for three donors of known Js phenotype: Js(a+b-), Js(a-b+), and Js(a+b+). Genotyping results for the 1910 SNP were identical to the phenotyping results in all 64 subjects, but for the 2019 SNP, the genotyping and phenotyping results were identical for only 49 subjects. In 12 subjects with the Js(a-b+) phenotype, the 2019 SNP was heterozygous KEL6, KEL7; in 2 with Js(a-b+) and in 1 with Js(a+b+), the 2019 SNP was homozygous KEL6.
Conclusion: KEL 2019-bp SNP does not always correlate with the Js phenotype owing to the presence of an atypical KEL gene with a KEL7 polymorphism at 1910 and a KEL6 polymorphism at 2019. The KEL polymorphism at 2019 is silent and this allele yields a Js(a-b+) phenotype. Only analysis of the 1910-bp SNP can be used to genotype KEL6 and KEL7.