Phenotype prediction by DNA-based typing of clinically significant blood group systems in Jordanian blood donors.

BACKGROUND AND OBJECTIVES: During the past 10 years several DNA-typing methods have been developed to complement routine serological typing for determination of polymorphisms in the ABO, RH, KEL, JK and FY blood group genes. However, the molecular basis of blood groups can differ widely between ethnic groups. The purpose of this study was to evaluate selected DNA-based methods for phenotype prediction in a population not previously investigated. MATERIALS AND METHODS: Blood samples from a random sample of Jordanian blood donors were collected and red cells isolated from these blood samples were phenotyped for common ABO (n = 150) and KEL/FY/JK (n = 90) antigens. RHD-negative and -positive donors were selected for RH typing (n = 120 and 30, respectively). DNA was prepared and blood group genotyping performed according to selected methods in current use. Discordant samples required further investigation by extended serology and DNA sequencing. RESULTS: The degree of concordance between phenotype and genotype was high, but some exceptions were noted. Two of 14 A2/A2B samples lacked all mutations associated with known A2 alleles of the ABO system. RH typing revealed four samples with the c(cyt48) marker, causing false-positive RHC typing. A single D-negative sample was positive for D-specific exon 10 markers. The RHD pseudogene was not found in the 150 donors tested. Nine samples revealed discrepancies that were associated with unknown silent or weakly expressing Fyb-like alleles. CONCLUSIONS: With the exception of the FY system, we conclude that the molecular background of the clinically important blood group antigens studied here is similar to that reported for Caucasoids.

Genomic analysis of clinical samples with serologic ABO blood grouping discrepancies: identification of 15 novel A and B subgroup alleles.

Since the cloning in 1990 of complementary DNA corresponding to messenger RNA transcribed at the blood group ABO locus, polymorphisms and phenotype-genotype correlations have been reported by several investigators. Exons 6 and 7, constituting 77% of the gene, have been analyzed previously in samples with variant phenotypes but for many subgroups the molecular basis remains unknown. This study analyzed 324 blood samples involved in ABO grouping discrepancies and determined their ABO genotype. Samples from individuals found to have known subgroup alleles (n = 53), acquired ABO phenotypes associated with different medical conditions (n = 65), probable chimerism (n = 3), and common red blood cell phenotypes (n = 109) were evaluated by ABO genotype screening only. Other samples (n = 94) from apparently healthy donors with weak expression of A or B antigens were considered potential subgroup samples without known molecular background. The full coding region (exons 1-7) and 2 proposed regulatory regions of the ABO gene were sequenced in selected A (n = 22) or B (n = 12) subgroup samples. Fifteen novel ABO subgroup alleles were identified, 2 of which are the first examples of mutations outside exon 7 associated with weak subgroups. Each allele was characterized by a missense or nonsense mutation for which screening by allele-specific primer polymerase chain reaction was performed. The novel mutations were encountered in 28 of the remaining 60 A and B subgroup samples but not among normal donors. As a result of this study, the number of definable alleles associated with weak ABO subgroups has increased from the 14 previously published to 29.

Genomic characterization of the kidd blood group gene:different molecular basis of the Jk(a-b-) phenotype in Polynesians and Finns.

BACKGROUND: The clinically important Kidd (JK) blood group antigens are carried by the urea transporter in red cells. The rare Jk(a-b-) phenotype can be caused by homozygosity at the JK locus for a silent allele, JK: This phenotype has been recorded in many ethnic groups, but it is most abundant among people originating from the Polynesian Islands and Finland. The molecular basis for Jk(a-b-) is unknown in these populations. STUDY DESIGN AND METHODS: Blood samples from individuals of Swedish, Polynesian, and Finnish origin were collected and characterized by routine JK blood group serology and JK genotyping. Genomic DNA covering the exons and intervening introns of the JK gene coding region was amplified by polymerase chain reaction, and fragments were directly sequenced. RESULTS: Exon and partial intron sequences in the coding region of the JK gene were determined. Finnish and Polynesian Jk alleles were analyzed; the only deviations from consensus were a splice-site mutation (G-->A) in Polynesians, causing skipping of exon 6, and a T871C substitution predicted to disrupt a potential N-glyco-sylation motif (NSS-->NSP) in Finns. Methods for rapid detection of silent Jk alleles were developed for clinical application. CONCLUSION: Polynesians and Finns have two different molecular alterations in their Jk alleles, both of which can now be determined by polymerase chain reaction.

Allele-related variation in minisatellite repeats involved in the transcription of the blood group ABO gene.

Since the cloning in 1990 of cDNA corresponding to mRNA transcribed at the blood group ABO locus, polymorphisms at the ABO locus and phenotype-genotype correlation have been analysed by several investigators. An enhancer-active minisatellite motif reported to contain four 43-bp repeats has been analysed by PCR in blood samples from 160 random Swedish blood donors. Different sizes of the DNA fragments obtained led to further analysis by direct sequencing. Fragments with either one or four 43-bp repeats were identified. A nucleotide substitution (G-->A) at nt. 41 of 43 was found in all alleles with only one repeat. Correlation with the ABO genotypes of the samples, as determined by a panel of ABO genotyping techniques, revealed an allele-related variable number of tandem repeats (VNTR). The A1 and the infrequent O2 allele had only one repeat whilst A2, B, O1 and O1v had four repeats and thus generated longer (by 129 bp) fragments. A further 74 samples obtained from various geographical areas/ethnic groups indicated a widespread correlation with few exceptions. In conclusion, a novel ABO polymorphism located in the 5'-nontranslated region involved in transcriptional regulation of the ABO gene is reported and its relationship to common alleles at this locus defined.

Genomic typing of the Kidd blood group locus by a single-tube allele-specific primer PCR technique.

The Kidd (JK) blood group system is clinically important in transfusion medicine. Alloantibodies to antigens in this system may be produced following blood transfusion or during pregnancy and can result in serious haemolytic transfusion reactions and haemolytic disease of the newborn (HDN). JK antigens on erythrocytes are carried by glycoproteins with the capacity to transport urea through cell membranes. cDNA complementary to mRNA transcribed at the JK locus was cloned in 1994. The molecular basis of the Jk(a)/Jk(b) blood group polymorphism was recently shown to be a single nucleotide substitution predicting an amino acid change (Asp280Asn) in an extracellular loop of the JK glycoprotein. After confirmation of the JK gene polymorphism we developed a rapid and robust technique for JK genotyping with allele-specific primers in a single-tube PCR. In addition, a 217 bp intron located at nucleotides 811-812 in the JK gene was found and sequenced. The genotyping test was validated with samples from 106 Caucasian Swedish and 13 Black South African random blood donors. Complete phenotype-genotype correlations were obtained. However, four Jk(a-b-) samples of Polynesian and Finnish origin typed as Jk(b)Jk(b). Potential use of the presented method can be predicted in clinical transfusion medicine including prenatal determination of the JK genotype in a fetus at risk for HDN caused by JK antibodies.