Background: The Knops blood group system consists of antigens encoded by exon 29 of complement receptor 1 (CR1) gene. To better elucidate the complexity of Knops group system, the frequency of six single-nucleotide polymorphisms (SNPs) in three Brazilian populations is determined.
Study design and methods: A total of 118 individuals descendant from Europe, Asia, and Africa were studied. The genomic fragment of CR1 was amplified by polymerase chain reaction, and the SNPs and haplotypes were determined after DNA sequence analysis.
Results: Among the six polymorphisms characterized, one of them was described for the first time. The analysis of allele frequency showed that these six SNPs did not differ between the European and Asian groups. The African group presented a higher frequency of alleles McC(b), Sl2, and KAM+. The six polymorphisms gave origin to 12 haplotypes that were defined for the first time. The haplotypes 1 (4646A, Kn(a), McC(a), Sl1, Sl4, KAM+), 2 (4646A, Kn(a), McC(a), Sl1, KAM-), and 3 (4646A, Kn(a), McC(a), Sl2, Sl4, KAM-) are the most frequent in all populations. The H2 presents similar frequency in all populations; however, whereas the H1 presented a higher prevalence in the European and Asian groups, in the African group H3 was present in a higher prevalence.
Conclusions: In this study, a new SNP substituting serine for asparagine at amino acid 1540 was identified. Moreover 12 haplotypes were identified. The differences in haplotype frequencies strongly suggest that the H1 and H2 might be the ancestral one while the H3 may have originated in Africa and may have fixed there by positive selection.