Multicolor real-time PCR genotyping of ABO system using displacing probes

The increasing need for ABO blood group genotyping and quality assurance implications for laboratory implementation

ABO blood group antigens are critical determinants of immunologic self and non-self and are ubiquitously expressed on all cellular tissues. Antibodies against non-self ABO antigens are naturally present and can mediate pathologic reactions against incompatible transfused blood cells and transplanted tissues. Laboratory testing for ABO antigens and isoagglutinins is essential for safe and effective transfusion and transplantation. Testing for ABO antigens has traditionally depended on serologic testing. However, there is increasing need for evaluation of genetic analysis of ABO antigens, to enable evaluation of ABO blood group in cases where serologic testing may be ambiguous or impossible to accurately perform. The clinical need for ABO genotyping is being addressed by the development of multiple molecular diagnostic approaches. Recent data have clearly demonstrated the potential utility of ABO genotyping in solid organ transplantation, yet widespread implementation has been slow. We propose that this lag is related to practical considerations in laboratory testing, including limited regulatory guidance on the performance and reporting of these assays and the absence of widely available external proficiency testing programs for quality assurance. Here we describe approaches to ABO genotyping, current initiatives in developing ABO genotyping proficiency testing programs, and laboratory quality assurance considerations for ABO genotyping.

Detection of five common variants of ABO gene by a triplex probe-based fluorescence-melting-curve-analysis

Current studies have suggested that the ABO blood group system is associated with several clinical conditions. For large-scale genotyping of ABO alleles, we developed a triplex fluorescence melting curve analysis (FMCA) to determine five single nucleotide variants (SNVs), c.261delG, c.796C>A, c.802G>A and c.803G>C and c.1061delC, responsible for common ABO phenotypes using dual-labeled self-quenched (TaqMan) probes in a single tube. We accurately determined c.796C>A, c.802G>A, and c.803G>C genotypes using a FAM-labeled probe, c.261delG using a CAL Fluor Orange 560- labeled probe, and c.1061delC using a Cy5-labeled probe. The present genotyping results of five SNVs in 214 subjects of the 1000 Genomes Project were in full agreement with those of the database sequence. The predicted ABO phenotypes using combinations of these five SNVs by this method in 288 Japanese subjects were in complete agreement with those by hemagglutination assay, although we did not find any A2 (alleles containing c.1061delC) or O.02 (alleles containing c.802G>A) alleles. The present triplex probe-based FMCA is a valid and credible method for a considerably accurate large-scale determination of ABO allele genotypes and estimation of phenotypes.

Rapid and Reliable One-Step ABO Genotyping Using Direct Real-Time Allele-Specific PCR and Melting Curve Analysis Without DNA Preparation

ABO genotyping is a molecular diagnostic technique important for transfusion and transplantation in medicine, and human identification in forensic science. Because ABO genotyping are labor intensive and time consuming, the genotyping cannot be firstly used to resolve the serological ABO discrepancy in blood bank. For rapid one-step ABO genotyping, we developed direct, real-time, allele-specific polymerase chain reaction (PCR), and melting curve analysis (DRAM assay) without DNA preparation. In DRAM assay, we used a special PCR buffer for direct PCR, a rapid RBC lysis buffer, white blood cells as template without DNA preparation, allele-specific primers for discriminating three ABO alleles (261G/del, 796C/A, and 803G/C), and melting curve analysis as a detection method. There was 100% concordance among the results of ABO genotyping by the DRAM assay, serologic typing, PCR-RFLP and PCR-direct sequencing of 96 venous blood samples. We were able to reduce the number of manual steps to three and the hands-on time to 12 min, compared to seven steps and approximately 40 min for conventional ABO genotyping using allele-specific PCR with purified DNA and agarose gel electrophoresis. We have established and validated the DRAM assay for rapid and reliable one-step ABO genotyping in a closed system. The DRAM assay with an appropriate number of allele-specific primers could help in resolving ABO discrepancies and should be valuable in clinical laboratory and blood bank.

Sex-specific differences in the association between ABO genotype and gastric cancer risk in a Korean population

BACKGROUND

Although previous studies have demonstrated an association between ABO blood group and the risk of gastric cancer (GC), only one study has identified these associations using the ABO genotype; however, that study did not evaluate sex differences in this association. The aim of the present study was to investigate whether there are sex-specific differences in the ABO genotype-associated risk of GC. In addition, we explored the association of the ABO genotype and the clinicopathologic characteristics of GC in a Korean population.

METHODS

We conducted a large-scale case-control study of 3245 GC patients (2204 males, 1041 females) and 1700 controls (821 males, 879 females). The ABO genotype was determined by multicolor real-time polymerase chain reaction (PCR) using displacing probes.

RESULTS

As compared with genotype OO, genotypes AA and AO in females, but not in males, were associated with a significantly increased risk of GC (odds ratio [OR] 1.56 and 95 % confidence interval [CI] 1.08-2.26 for AA; OR 1.57 and 95 % CI 1.21-2.03 for AO). In a subgroup analysis, blood group A had a significantly increased risk of diffuse-type GC (OR 2.00, 95 % CI 1.43-2.78), but not of intestinal-type (OR 1.31, 95 % CI 0.96-1.79) or mixed-type GC (OR 1.43, 95 % CI 0.92-2.24).

CONCLUSION

The ABO genotypes AA and AO were significantly associated with GC only in females and only for diffuse-type GC. These data suggest that the association between ABO blood group and GC risk may differ according to sex and histological type.

ABO genotyping by TaqMan assay and allele frequencies in a Japanese population

ABO genotyping have become common tools for forensic casework. We developed a new rapid ABO genotyping method using a fast real-time PCR system with the TaqMan® Sample-to-SNP™ Kit. Eight single nucleotide polymorphism (SNP) sites in the ABO gene (nt 261, 297, 467, 657, 703, 829, 930 and 1061) were selected to determine the ABO genotypes. ABO genotypes were easily determined by examining allelic discrimination patterns. This method enabled analyses to be completed in about 1h per plate with no postmortem change influences. The detection limit in each SNP site was examined as 100pg per reaction. ABO genotyping from 1000 Japanese individuals was also examined to determine the distribution of ABO genotypes and allele frequencies. Thus, 31 genotypes were clearly identified, and these were controlled by four common and seven rare alleles. The power of discrimination, heterozygosity and polymorphism information contents were 0.913, 0.775 and 0.812, respectively. Therefore, selecting these eight SNP sites could be useful for high specific ABO genotyping. This rapid, sensitive and accurate genotyping method is useful for forensic casework.

ABO blood group genotyping by quenching probe method

We developed a multiplex ABO genotyping method with quenching probes (Q-probe). In this method, it is possible to discriminate the mutations, not only frequently used positions 261 and 796 but also position 703 in a single PCR. Each probe was designed to have cytosine residue at 5' or 3' end and labeled with three different fluorescence dyes, enabling the triplex detections of these polymorphisms. All polymorphisms were successfully detected by using fluorescence labeled Q-probe in a specifically amplified PCR product. Each Q-probe showed unique dissociation patterns depending on the polymorphism types. All of the results obtained with Q-probe were compared with standard serotyping and TaqMan PCR method and resulted in complete match with each other. Consequently, these results indicated that multiplex ABO genotyping method is quite accurate and convenient method for the determination of ABO genotype.

An integrated system of ABO typing and multiplex STR testing for forensic DNA analysis

A new amplification system for ABO and STR genotyping in a single reaction has been successfully developed. Two types of information can be obtained from a biological sample at one time. One is the classical information of ABO blood group typing for screening suspects and the other is STR information for individual identification. The system allows for the simultaneous detection of 15 autosomal STR loci (containing all CODIS STR loci as well as Penta D and Penta E), six ABO genotypes (O/O, B/B, A/A, A/O, A/B, and B/O) and the gender-determining locus Amelogenin. Primers are designed so that the amplicons are distributed ranging from 75bp to 500bp within a four-dye fluorescent design, leaving a fourth dye for the internal size standard. With 30 cycles, the results showed that the optimal amount of DNA template for this multiplex ranges from 250pg to 2ng and the lowest detection threshold is 125pg (as low as 63pg for ABO loci). For the DNA template outside the optimal detection range, we could adjust the number of cycles to obtain the robust profiles. Mixture studies showed that over 83% of minor alleles were detected at 1:9 ratios. The full profiles were still observed when 4ng of degraded DNA was digested by DNase I and 1ng undegraded DNA was added to 40μM haematin. Polymerase chain reaction (PCR)-based conditions including the concentrations of primers, magnesium and the Taq polymerase as well as volume, cycle numbers and annealing temperature were examined and optimised. In addition, the system was validated by 364 bloodstain samples and 32 common casework samples. According to the Chinese National Standards and Scientific Working Group on DNA Analysis Methods (SWGDAM) guidelines, our system demonstrates good detection performance and is an ideal tool for forensic DNA typing with potential application.

Determination of ABO genotypes by real-time PCR using allele-specific primers

ABO grouping of biological specimens is informative for identifying victims and narrowing down suspects. In Japan and elsewhere, ABO grouping as well as DNA profiling plays an essential role in crime investigations. In the present study, we developed a new method for ABO genotyping using allele-specific primers and real-time PCR. The method allows for the detection of three single nucleotide polymorphisms (SNPs) at nucleotide positions 261, 796, and 803 in the ABO gene and the determination of six major ABO genotypes. This method required less than 2 h for accurate ABO genotyping using 2.0 ng of DNA. This method could be applicable for rapid and simple screening of forensic samples.