A simple, bead-based approach for multi-SNP molecular haplotyping

Quantum-dot-based suspension microarray for multiplex detection of lung cancer markers: preclinical validation and comparison with the Luminex xMAP® system

A novel suspension multiplex immunoassay for the simultaneous specific detection of lung cancer markers in bronchoalveolar lavage fluid (BALF) clinical samples based on fluorescent microspheres having different size and spectrally encoded with quantum dots (QDEM) was developed. The designed suspension immunoassay was validated for the quantitative detection of three lung cancer markers in BALF samples from 42 lung cancer patients and 10 control subjects. Tumor markers were detected through simultaneous formation of specific immune complexes consisting of a capture molecule, the target antigen, and biotinylated recognition molecule on the surface of the different QDEM in a mixture. The immune complexes were visualized by fluorescently labeled streptavidin and simultaneously analyzed using a flow cytometer. Preclinical validation of the immunoassay was performed and results were compared with those obtained using an alternative 3-plex immunoassay based on Luminex xMAP^® technology, developed on classical organic fluorophores. The comparison showed that the QDEM and xMAP^® assays yielded almost identical results, with clear discrimination between control and clinical samples. Thus, developed QDEM technology can become a good alternative to xMAP^® assays permitting analysis of multiple protein biomarkers using conventional flow cytometers.

Adoption of array technologies into the clinical laboratory

Array-based methods are making substantial contributions to the discovery of disease biomarkers and are fueling the growth of multianalyte testing for disease diagnosis and treatment. The distillation of high-density array results into sets of signature markers promises to improve disease staging, risk stratification and treatment decisions. To accommodate the growing requirement for multiplex testing, clinical laboratories are converting several single-analyte tests into array-based formats. However, adoption of array technologies provides several challenges to the laboratory, which must evaluate these new formats, train laboratory personnel, market the new services and obtain reimbursement for new analytes. Liquid-bead arrays are an attractive format for routine clinical diagnostics due to a combination of appropriate analyte density, simultaneous array decoding and detection, and flexibility for rapid customization. In this review, the suitability of several array platforms to diagnostic testing and applications of liquid-bead arrays for cystic fibrosis testing, multidisease carrier status assays and leukemia subtyping are discussed. As our understanding of the clinical utility of new or established biomarkers and recommendations for testing change, flexibility and adaptability of array platforms will be imperative. Future development of novel assay formats and improved quantitation will expand the number of diseases tested and lead to further integration into the diagnostic laboratory.

Multiplexed suspension array platform for high-throughput protein assays

A multiplexed suspension array platform, based on SU8 disks patterned with machine-readable binary identification codes is presented. Multiple probe molecules, each attached to individual disks with different unique codes, provide multiplexed detection of targets in a small sample volume. The experimental system consists of a microfluidic chamber for arraying the particles in a manner suitable for high throughput imaging using a simple fluorescent microscope, together with custom software for automated code readout and analysis of assay response. The platform is demonstrated with a multiplexed antibody assay targeting 3 different human inflammatory cytokines. The suitability of the platform for other bio-analytical applications is discussed.

High-resolution melting analysis for SNP genotyping and mapping in tetraploid alfalfa (Medicago sativa L.)

Single nucleotide polymorphisms (SNPs) represent the most abundant type of genetic polymorphism in plant genomes. SNP markers are valuable tools for genetic analysis of complex traits of agronomic importance, linkage and association mapping, genome-wide selection, map-based cloning, and marker-assisted selection. Current challenges for SNP genotyping in polyploid outcrossing species include multiple alleles per loci and lack of high-throughput methods suitable for variant detection. In this study, we report on a high-resolution melting (HRM) analysis system for SNP genotyping and mapping in outcrossing tetraploid genotypes. The sensitivity and utility of this technology is demonstrated by identification of the parental genotypes and segregating progeny in six alfalfa populations based on unique melting curve profiles due to differences in allelic composition at one or multiple loci. HRM using a 384-well format is a fast, consistent, and efficient approach for SNP discovery and genotyping, useful in polyploid species with uncharacterized genomes. Possible applications of this method include variation discovery, analysis of candidate genes, genotyping for comparative and association mapping, and integration of genome-wide selection in breeding programs. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11032-011-9566-x) contains supplementary material, which is available to authorized users.

Application of multiple response optimization design to quantum dot-encoded microsphere bioconjugates hybridization assay

The optimization of DNA hybridization for genotyping assays is a complex experimental problem that depends on multiple factors such as assay formats, fluorescent probes, target sequence, experimental conditions, and data analysis. Quantum dot-doped particle bioconjugates have been previously described as fluorescent probes to identify single nucleotide polymorphisms even though this advanced fluorescent material has shown structural instability in aqueous environments. To achieve the optimization of DNA hybridization to quantum dot-doped particle bioconjugates in suspension while maximizing the stability of the probe materials, a nonsequential optimization approach was evaluated. The design of experiment with response surface methodology and multiple optimization response was used to maximize the recovery of fluorescent probe at the end of the assay simultaneously with the optimization of target-probe binding. Hybridization efficiency was evaluated by the attachment of fluorescent oligonucleotides to the fluorescent probe through continuous flow cytometry detection. Optimal conditions were predicted with the model and tested for the identification of single nucleotide polymorphisms. The design of experiment has been shown to significantly improve biochemistry and biotechnology optimization processes. Here we demonstrate the potential of this statistical approach to facilitate the optimization of experimental protocol that involves material science and molecular biology.

SNP assay to detect the 'Hyuuga' red-brown lesion resistance gene for Asian soybean rust

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi Syd., has the potential to become a serious threat to soybean, Glycine max L. Merr., production in the USA. A novel rust resistance gene, Rpp?(Hyuuga), from the Japanese soybean cultivar Hyuuga has been identified and mapped to soybean chromosome 6 (Gm06). Our objectives were to fine-map the Rpp?(Hyuuga) gene and develop a high-throughput single nucleotide polymorphism (SNP) assay to detect this ASR resistance gene. The integration of recombination events from two different soybean populations and the ASR reaction data indicates that the Rpp?(Hyuuga) locus is located in a region of approximately 371 kb between STS70887 and STS70923 on chromosome Gm06. A set of 32 ancestral genotypes which is predicted to contain 95% of the alleles present in current elite North American breeding populations and the sources of the previously reported ASR resistance genes (Rpp1, Rpp2, Rpp3, Rpp4, Rpp5, and rpp5) were genotyped with five SNP markers. We developed a SimpleProbe assay based on melting curve analysis for SNP06-44058 which is tighly linked to the Rpp?(Hyuuga) gene. This SNP assay can differentiate plants/lines that are homozygous/homogeneous or heterozygous/heterogeneous for the resistant and susceptible alleles at the Rpp?(Hyuuga) locus.

g you The direct determination of haplotypes from extended regions of genomic DNA

BACKGROUND

One of the major obstacles to the exploitation of genetic variation in human medicine, veterinary medicine, and animal breeding is the difficulty in defining haplotypes in unrelated individuals.

RESULTS

We have developed a Multiplex Double Amplification Refractory Mutation System combined with Solid Phase PCR on Fluorescently labelled beads. The process is inherently amenable to automation. It provides a high degree of internal Quality Control, as each PCR product is represented in duplicate on the bead array, and each SNP is tested against multiple partners. This technique can resolve very complex genotypes into their constituent haplotypes; it defined all the alleles at 60 SNP in exon 2 of the ovine DRB1 MHC locus in a sample of 109 rams. These 60 SNP formed 33 DRB1 exon 2 alleles; two of which had not been previously identified; although both of them have been independently confirmed.

CONCLUSION

This technique has the same resolution as allele specific sequencing. Sequencing has the advantage of identifying novel polymorphic sites but where all SNP sites have been identified this novel procedure can resolve all alleles and haplotypes and identify novel combinations of polymorphisms. This method is similar in price to direct sequencing and provides a low cost system for direct haplotyping of extended DNA sequences.

Search for genetic markers and functional variants involved in the development of opiate and cocaine addiction and treatment

Addiction to opiates and illicit use of psychostimulants is a chronic, relapsing brain disease that, if left untreated, can cause major medical, social, and economic problems. This article reviews recent progress in studies of association of gene variants with vulnerability to develop opiate and cocaine addictions, focusing primarily on genes of the opioid and monoaminergic systems. In addition, we provide the first evidence of a cis-acting polymorphism and a functional haplotype in the PDYN gene, of significantly higher DNA methylation rate of the OPRM1 gene in the lymphocytes of heroin addicts, and significant differences in genotype frequencies of three single-nucleotide polymorphisms of the P-glycoprotein gene (ABCB1) between "higher" and "lower" methadone doses in methadone-maintained patients. In genomewide and multigene association studies, we found association of several new genes and new variants of known genes with heroin addiction. Finally, we describe the development and application of a novel technique: molecular haplotyping for studies in genetics of drug addiction.

Microparticle encoding technologies for high-throughput multiplexed suspension assays

The requirement for analysis of large numbers of biomolecules for drug discovery and clinical diagnostics has driven the development of low-cost, flexible and high-throughput methods for simultaneous detection of multiple molecular targets in a single sample (multiplexed analysis). The technique that seems most likely to satisfy all of these requirements is the multiplexed suspension (bead-based) assay, which offers a number of advantages over alternative approaches such as ELISAs and microarrays. In a bead based assay, different probe molecules are attached to different beads (of a few tens of microns in size), which are then reacted in suspension with the target sample. After reaction, the beads must be identifiable in order to determine the attached probe molecule, and thus each bead must be labelled (encoded) with a unique identifier. A large number of techniques have been proposed for encoding beads. This critical review analyses each technology on the basis of its ability to fulfil the practical requirements of assays, whilst being compatible with low-cost, high-throughput manufacturing processes and high-throughput detection methods. As a result, we identify the most likely candidates to be used for future integrated device development for practical applications.

Fluorescent nanocrystal-encoded microbeads for multiplexed cancer imaging and diagnosis

Bead-based assays on very large numbers of molecules in proteomics, genomics, drug screening and clinical diagnostics require encoding of each of the microbeads according to the particular ligand bound to its surface. The benefits of using optically encoded microbeads (instead of the solid-state two-dimensional arrays) are derived from the freedom of bead to move in three dimensions. Polymeric beads optically encoded with organic dyes allow for a limited number of unique codes whereas the use of semiconductor nanocrystals as fluorescent tags improves the beads multiplexed imaging capabilities, photostability and sensitivity of the antigen detection. Additionally, an employment of the recently demonstrated Förster resonance energy transfer (FRET) from the microbeads nanocrystal codes to the nearby antibody dye label allows for the very specific detection of the interaction between the microbead and the antibody. This interaction turns the fluorescence signal from dye label off and on thus effectively discriminating between the occurrence and the non-occurrence of antibody binding. The absence of fluorescent background from non-interacting with the beads dye-labelled antibodies additionally increases the sensitivity of detection and further facilitates the multiplexing capabilities of nanocrystals-based detection and diagnostics. This paper reviews the state-of-the-art results of development of microbeads optically encoded with the fluorescent nanocrystals "quantum dots" and their applications to proteomics for cancer antigens and autoantibodies imaging and diagnosis.

Haplotype reconstruction for scnp DNA: a consensus vote approach with extensive sequence data from populations of the migratory locust (Locusta migratoria)

Single copy nuclear polymorphic (scnp) DNA is potentially a powerful molecular marker for evolutionary studies of populations. However, a practical obstacle to its employment is the general problem of haplotype determination due to the common occurrence of heterozygosity in diploid organisms. We explore here a 'consensus vote' (CV) approach to this question, combining statistical haplotype reconstruction and experimental verification using as an example an indel-free scnp DNA marker from the flanking region of a microsatellite locus of the migratory locust. The raw data comprise 251-bp sequences from 526 locust individuals (1052 chromosomes), with 71 (28.3%) polymorphic nucleotide sites (including seven triallelic sites) and 141 distinct genotypes (with frequencies ranging from 0.2 to 25.5%). Six representative statistical haplotype reconstruction algorithms are employed in our CV approach, including one parsimony method, two expectation-maximization (EM) methods and three Bayesian methods. The phases of 116 ambiguous individuals inferred by this approach are verified by molecular cloning experiments. We demonstrate the effectiveness of the CV approach compared to inferences based on individual statistical algorithms. First, it has the unique power to partition the inferrals into a reliable group and an uncertain group, thereby allowing the identification of the inferrals with greater uncertainty (12.7% of the total sample in this case). This considerably reduces subsequent efforts of experimental verification. Second, this approach is capable of handling genotype data pooled from many geographical populations, thus tolerating heterogeneity of genetic diversity among populations. Third, the performance of the CV approach is not influenced by the number of heterozygous sites in the ambiguous genotypes. Therefore, the CV approach is potentially a reliable strategy for effective haplotype determination of nuclear DNA markers. Our results also show that rare variations and rare inferrals tend to be more vulnerable to inference error, and hence deserve extra surveillance.

Layer-by-layer coated digitally encoded microcarriers for quantification of proteins in serum and plasma

The "layer-by-layer" (LbL) technology has been widely investigated for the coating of flat substrates and capsules with polyelectrolytes. In this study, LbL polyelectrolyte coatings applied at the surface of digitally encoded microcarriers were evaluated for the quantitative, sensitive, and simultaneous detection of proteins in complex biological samples like serum, plasma, and blood. LbL coated microcarriers were therefore coupled to capture antibodies, which were used as capture agents for the detection of tumor necrosis factor (TNF-alpha), P24, and follicle stimulating hormone (FSH). It was found that the LbL coatings did not disassemble upon incubating the microcarriers in serum and plasma. Also, nonspecific binding of target analytes to the LbL coating was not observed. We showed that the LbL coated microcarriers can reproducibly detect TNF-alpha, P24, and FSH down to the picogram per milliliter level, not only in buffer but also in serum and plasma samples. Microcarrier-to-microcarrier intratube variations were less then 30%, and interassay variations less than 8% were observed. This paper also shows evidence that the LbL coated digitally encoded microcarriers are ideally suited for assaying proteins in "whole" blood in microfluidic chips, which are of high interest for "point-of-care" diagnostics.

Determination of the optimized conditions for coupling oligonucleotides with 16-mercaptohexadecanoic acid chemically adsorbed upon Au

A specific 5'-modified amino group oligonucleotide (Primer 1), 15-mers in length, is selectively coupled with the carboxyl terminated 16-mercaptohexadecanoic acid (MHDA) chemically adsorbed on Au and subsequently hybridized with Antisense Primer. The amide-coupling process is of significance to create an intermediate structure for the purpose of adding Primer 1, while the hybridization reaction is relevant to various diagnostic purposes to determine the presence in nucleic acids for a target sequence. In this work, the coupling setting was particularly emphasized by varying commonly used temperatures and pH values with a definite concentration of coupling agents (i.e., 10 mM). The recombination with analogous hybridization treatment was investigated using high resolution X-ray photoelectron spectroscopy and a 75 degrees grazing angle Fourier transform infrared spectrometer. On the basis of the spectroscopic studies, the optimized conditions for the coupling process that is also correlated with the molecular density of subsequent hybridization process on MHDA/Au have been proposed at 37 degrees C and a pH value of 4.5. Therefore, it is pertinent to intensify the joining of short-chain DNA strands by complementary base pairing in diagnostic applications such as the identification of single nucleotide polymorphisms.

Luminescence decay time encoding of magnetic micro spheres for multiplexed analysis

Magnetic microspheres are optically encoded by doping with three luminescent dyes. The combination of a fluorophore with a nanosecond decay profile and two phosphorescent Ruthenium metal ligand complexes with a microsecond decay profile generates a characteristic signature described by three features: bead brightness, luminescent decay time and dual lifetime referencing (DLR). The beads are identified by time resolved imaging in the microsecond range. A series of fluorophores is tested and the interference of the resulting luminescent code in the red and green label detection channels is investigated. A detailed staining procedure is worked out to increase the staining efficiency of the dyes with hydrophilic character into the lipophilic polystyrene microspheres. A mathematical model is established to calculate the dye amounts that are needed for staining a bead family with a specific feature set. Nineteen bead families were prepared representing the grid points in the three planes of a cube referring to the three features. The coefficient of variation over all bead families is 7%, 1.4% and 1.6% for bead brightness, luminescence decay time and DLR, respectively. The combination of these features and the bead size as additional feature enables the creation of 840 distinguishable bead families.

Encoded microcarriers for high-throughput multiplexed detection

Since the decoding of the human genome, the quest to obtain more and more molecular information from smaller and smaller samples is intensifying. Today the burden of this challenge is being borne by planar arrays, but the quality of the data provided by this approach is limited by variations in performance between different arrays. Suspension arrays of encoded microspheres provide higher quality data, but the amount of molecular information that can be acquired with them is limited by the number of codes that can be distinguished in the same sample. New methods of preparing encoded particles promise to alleviate this problem, but in the face of a growing number of new technologies it is sometimes difficult to decide which, if any, will succeed. Herein we appraise these new forms of encoded particle critically, and ask if they can deliver the necessary multiplexing power and whether they will perform well in multiplexed assays.

Determination of CYP2D6, CYP2C9 and CYP2C19 genotypes with Tag-It mutation detection assays

Cytochrome P450 (CYP) genotyping can be used to prospectively identify individuals at risk for adverse drug reactions or therapeutic failure due to altered drug metabolism. Based on the specific CYP(s) affected, individuals may require less or more of a particular drug than people with unaffected CYP-mediated metabolism, or may be best managed by avoiding certain drugs entirely. Here we evaluated the Tag-It CYP mutation detection reagents (Tm Bioscience Corp.). As these reagents, based on a universal bead array, detect more than 20 clinically significant variants common to different ancestries, it was important to consider DNA from genetically diverse populations. Thus, we also report CYP2D6, CYP2C9 and CYP2C19 genotypes for DNA available through the Coriell Institute for Medical Research (NJ, USA). These samples represent individuals from Caucasian, Japanese, Chinese, Southeast Asian, African-American and Middle Eastern ancestry, and provide an excellent resource for evaluating and validating CYP genotyping methods. Using these samples, the Tag-It mutation detections assays reliably provided genotypes for CYP2D6, CYP2C9 and CYP2C19. The CYP2C9 and CYP2C19 assays were particularly robust and were easily implemented in our clinical laboratory. The CYP2D6 assay was somewhat less robust and could be improved by associating the 2850C>T variant with a specific allele, as well as by discriminating the allele affected when gene duplication is detected.

An efficient method for multi-locus molecular haplotyping

Many methods exist for genotyping—revealing which alleles an individual carries at different genetic loci. A harder problem is haplotyping—determining which alleles lie on each of the two homologous chromosomes in a diploid individual. Conventional approaches to haplotyping require the use of several generations to reconstruct haplotypes within a pedigree, or use statistical methods to estimate the prevalence of different haplotypes in a population. Several molecular haplotyping methods have been proposed, but have been limited to small numbers of loci, usually over short distances. Here we demonstrate a method which allows rapid molecular haplotyping of many loci over long distances. The method requires no more genotypings than pedigree methods, but requires no family material. It relies on a procedure to identify and genotype single DNA molecules, and reconstruction of long haplotypes by a ‘tiling’ approach. We demonstrate this by resolving haplotypes in two regions of the human genome, harbouring 20 and 105 single-nucleotide polymorphisms, respectively. The method can be extended to reconstruct haplotypes of arbitrary complexity and length, and can make use of a variety of genotyping platforms. We also argue that this method is applicable in situations which are intractable to conventional approaches.

Multiplexed and microparticle-based analyses: quantitative tools for the large-scale analysis of biological systems

While the term flow cytometry refers to the measurement of cells, the approach of making sensitive multiparameter optical measurements in a flowing sample stream is a very general analytical approach. The past few years have seen an explosion in the application of flow cytometry technology for molecular analysis and measurements using microparticles as solid supports. While microsphere-based molecular analyses using flow cytometry date back three decades, the need for highly parallel quantitative molecular measurements that has arisen from various genomic and proteomic advances has driven the development in particle encoding technology to enable highly multiplexed assays. Multiplexed particle-based immunoassays are now common place, and new assays to study genes, protein function, and molecular assembly. Numerous efforts are underway to extend the multiplexing capabilities of microparticle-based assays through new approaches to particle encoding and analyte reporting. The impact of these developments will be seen in the basic research and clinical laboratories, as well as in drug development.

Multilocus association mapping using variable-length Markov chains

I propose a new method for association-based gene mapping that makes powerful use of multilocus data, is computationally efficient, and is straightforward to apply over large genomic regions. The approach is based on the fitting of variable-length Markov chain models, which automatically adapt to the degree of linkage disequilibrium (LD) between markers to create a parsimonious model for the LD structure. Edges of the fitted graph are tested for association with trait status. This approach can be thought of as haplotype testing with sophisticated windowing that accounts for extent of LD to reduce degrees of freedom and number of tests while maximizing information. I present analyses of two published data sets that show that this approach can have better power than single-marker tests or sliding-window haplotypic tests.

Long-range multilocus haplotype phasing of the MHC

Haplotypes are a powerful tool for identifying the genetic basis of common complex diseases. Disease-association mapping requires molecular methods for haplotyping biallelic SNP variation and highly complex polymorphisms. We developed a method for phasing HLA-A, HLA-B, and HLA-DRB1 alleles on chromosome 6 in unrelated individuals. This method uses the highly polymorphic HLA-B locus to discriminate the two HLA haplotypes in heterozygous individuals and its ideal location 1.4 Mbp telomeric to HLA-DRB1 and 1.2 Mbp centromeric to HLA-A to capture 2-Mbp-long genomic DNA. Genomic DNA representing a single HLA-B-captured haplotype is genotyped for HLA-A and HLA-DRB1 alleles and linkage to HLA-B is established. Proof of principle was established in a large blinded study of phase-known samples. Availability of an efficient method for MHC haplotype phase determination will facilitate the mapping of causative MHC-resident genes in many human diseases and has the potential to be broadened to other polymorphic gene complexes.

Multiplex real-time single nucleotide polymorphism detection and quantification by quencher extension

Multiplex quencher extension (multiplex-QEXT) is a novel closed tube single-step method for detection and quantification of several single nucleotide polymorphisms (SNPs) simultaneously. The principle of multiplex-QEXT is that 5' reporter-labeled probes are 3' single-base-extended with TAMRA dideoxy nucleotides if the respective SNP alleles are present. TAMRA can serve as either an energy acceptor (quencher-based detection) or donor [fluorescence resonance energy transfer (FRET)-based detection] for a wide range of different reporter fluorochromes. The extension can therefore be recorded by the respective reporter fluorescence change. We evaluated multiplex-QEXT, analyzing four different SNP loci in the Listeria monocytogenes inlA gene. Probes labeled with the reporters 6-FAM, TET, VIC, and Alexa Fluor 594 were used. Responses for the fluorochromes 6-FAM, TET, and VIC were detected by quenching (decreased fluorescence), while the response for Alexa Fluor 594 was detected by FRET (increased fluorescence). We evaluated the SNP-allele pattern in 252 different L. monocytogenes strains. Multiplex-QEXT gave a good resolution, detecting seven major and five minor groups of L. monocytogenes. Comparison with serotyping showed that multiplex-QEXT gave better resolution. We also evaluated the quantitative aspects of multiplex-QEXT. Quantitative information was obtained for all the fluorochrome/probe combinations in the sample pools. The detection limits for 6-FAM, TET and Alexa Fluor 594 were the presence of the 10% target SNP alleles (P < 0.05), while the detection limit for VIC was the presence of the 5% target SNP alleles (P < 0.05). Currently, overlap in the fluorescence emission spectra is the limiting factor for the multiplexing potential of QEXT. With the emergence of new fluorochromes with narrow emission spectra, we foresee great potential for increasing the multiplex level in the future.

Simultaneous determination of 7 N-acetyltransferase-2 single-nucleotide variations by allele-specific primer extension assay

BACKGROUND

Genotyping of N-acetyltransferase-2 (NAT2) is useful in predicting the risk for toxicity of NAT2 substrates. Current methods cannot detect the 7 most important single-nucleotide variations in NAT2 simultaneously in 1 tube.

METHODS

We developed an assay that uses allele-specific primer extension (ASPE) and microsphere hybridization for the simultaneous detection of 7 single-nucleotide variations in NAT2. Using 12 samples previously genotyped by a TaqMan-based assay for method development and as positive controls, we amplified the genetic locus of NAT2 comprising the single-nucleotide variations of interest by PCR and then performed ASPE with allele-specific primers and biotinylated dCTP followed by bead hybridization and streptavidin-R-phycoerythrin binding. Genotypes were determined according to the allele-specific fluorescent signal ratios.

RESULTS

The mean (SD) allelic ratios for homozygous common, heterozygous variant, and homozygous variant NAT2 genotypes were 0.0394 (0.0113) (n = 80), 0.4372 (0.0270) (n = 148), and 0.9331 (0.0127) (n = 325). The assay had 100% (95% confidence interval, 99%-100%) within-run reproducibility for 12 samples repeated 6 times and 100% (98%-100%) between-run reproducibility for a 5-sample subset run on 6 different days. NAT2 genotypes of 30 blinded samples determined by this assay were 100% (98%-100%) concordant with results obtained using the TaqMan method.

CONCLUSIONS

The developed assay can simultaneously determine single-nucleotide variations in NAT2. The assay demonstrates no overlap in allele-specific signal ratios between homozygous common, heterozygous, and homozygous variant and shows agreement with a reference method and reproducibility of genotype identification.

Direct molecular haplotyping by melting curve analysis of hybridization probes: beta 2-adrenergic receptor haplotypes as an example

Direct determination of the association of multiple genetic polymorphisms, or haplotyping, in individual samples is challenging because of chromosome diploidy. Here, we describe the ability of hybridization probes, commonly used as genotyping tools, to establish single nucleotide polymorphism (SNP) haplotypes in a single step. Three haplotypes found in the beta 2-adrenergic receptor (beta2AR) gene and characterized by three different SNPs combinations are presented as examples. Each combination of SNPs has a unique stability, recorded by its melting temperature, even when intervening sequences from the template must loop out during probe hybridization. In the course of this study, two haplotypes in beta2AR not described previously were discovered. This approach provides a tool for molecular haplotyping that should prove useful in clinical molecular genetics diagnostics and pharmacogenetic research where methods for direct haplotyping are needed.