Qiuying Huang

Multiplex Fluorescence Melting Curve Analysis for Mutation Detection with Dual-Labeled, Self-Quenched Probes

Probe-based fluorescence melting curve analysis (FMCA) is a powerful tool for mutation detection based on melting temperature generated by thermal denaturation of the probe-target hybrid. Nevertheless, the color multiplexing, probe design, and cross-platform compatibility remain to be limited by using existing probe chemistries. We hereby explored two dual-labeled, self-quenched probes, TaqMan and shared-stem molecular beacons, in their ability to conduct FMCA. Both probes could be directly used for FMCA and readily integrated with closed-tube amplicon hybridization under asymmetric PCR conditions. Improved flexibility of FMCA by using these probes was illustrated in three representative applications of FMCA: mutation scanning, mutation identification and mutation genotyping, all of which achieved improved color-multiplexing with easy probe design and versatile probe combination and all were validated with a large number of real clinical samples. The universal cross-platform compatibility of these probes-based FMCA was also demonstrated by a 4-color mutation genotyping assay performed on five different real-time PCR instruments. The dual-labeled, self-quenched probes offered unprecedented combined advantage of enhanced multiplexing, improved flexibility in probe design, and expanded cross-platform compatibility, which would substantially improve FMCA in mutation detection of various applications.

A melting curve analysis--based PCR assay for one-step genotyping of β-thalassemia mutations a multicenter validation.

The increasing number of disease-causing mutations demands a simple, direct, and cost-effective diagnostic genotyping technique capable of detecting multiple mutations. This study validated the efficacy of a novel melting curve analysis-based genotyping assay (MeltPro HBB assay) for 24 β-thalassemia mutations in the Chinese population. The diagnostic potential of this assay was evaluated in 1022 pretyped genomic DNA samples, including 909 clinical cases of β-thalassemia minor or major, using a double-blind analysis in a multicenter validation study. Reproducibility of the assay was 100%, and the limit of detection was 10 pg per reaction. All 24 β-thalassemia mutations were accurately genotyped, and β-thalassemia genotypes were correctly determined in all 1022 samples, yielding overall sensitivity and specificity of 100%. The concordance rate was 99.4% between this assay and the reference method. It was concluded that the MeltPro HBB assay is useful for reliable genotyping of multiple β-thalassemia mutations in clinical settings and may have potential as a versatile method for rapid genotyping of known mutations because of its high throughput, accuracy, ease of use, and low cost.

Multicolor Combinatorial Probe Coding for Real-Time PCR

The target volume of multiplex real-time PCR assays is limited by the number of fluorescent dyes available and the number of fluorescence acquisition channels present in the PCR instrument. We hereby explored a probe labeling strategy that significantly increased the target volume of real-time PCR detection in one reaction. The labeling paradigm, termed “Multicolor Combinatorial Probe Coding” (MCPC), uses a limited number (n) of differently colored fluorophores in various combinations to label each probe, enabling one of 2n-1 genetic targets to be detected in one reaction. The proof-of-principle of MCPC was validated by identification of one of each possible 15 human papillomavirus types, which is the maximum target number theoretically detectable by MCPC with a 4-color channel instrument, in one reaction. MCPC was then improved from a one-primer-pair setting to a multiple-primer-pair format through Homo-Tag Assisted Non-Dimer (HAND) system to allow multiple primer pairs to be included in one reaction. This improvement was demonstrated via identification of one of the possible 10 foodborne pathogen candidates with 10 pairs of primers included in one reaction, which had limit of detection equivalent to the uniplex PCR. MCPC was further explored in detecting combined genotypes of five β-globin gene mutations where multiple targets were co-amplified. MCPC strategy could expand the scope of real-time PCR assays in applications which are unachievable by current labeling strategy.

Natural phage nanoparticle-mediated real-time immuno-PCR for ultrasensitive detection of protein marker

Current immuno-PCR methods either use bare or nanostructured DNA as a reporter or combine phage display for antigen binding and reporting, however, they are often complex to carry out and lack universality. We present a novel and universal design of immuno-PCR termed natural phage nanoparticle-mediated real-time immuno-PCR.

Combination of fluorescence color and melting temperature as a two-dimensional label for homogeneous multiplex PCR detection

Multiplex analytical systems that allow detection of multiple nucleic acid targets in one assay can provide rapid characterization of a sample while still saving cost and resources. However, few systems have proven to offer a solution for mid-plex (e.g. 10- to 50-plex) analysis that is high throughput and cost effective. Here we describe the combined use of fluorescence color and melting temperature (Tm) as a virtual 2D label that enables homogenous detection of one order of magnitude more targets than current strategies on real-time polymerase chain reaction platform. The target was first hybridized with a pair of ligation oligonucleotides, one of which harbored an artificial sequence that had a unique Tm when hybridized with a reporter fluorogenic probe. The ligated products were then amplified by a universal primer pair and denatured by a melting curve analysis procedure. The targets were identified by their respective Tm values in the corresponding fluorescence detection channels. The proof-of-principle of this approach was validated by genotyping 15 high-risk human papillomaviruses and 48 human single-nucleotide polymorphisms. The robustness of this method was demonstrated by analyzing a large number of clinical samples in both cases. The combined merits of multiplexity, flexibility and simplicity should make this approach suitable for a variety of applications.

Preparation of a Chimeric Armored RNA as a Versatile Calibrator for Multiple Virus Assays

As with all diagnostic techniques, molecular testing requires careful quality control (1)(2)(3). In detection of RNA viruses, which are often present at low concentrations and are prone to degradation, stringent monitoring is needed for all aspects of assay performance, including virus lysis, RNA isolation, reverse transcription, amplification, and detection steps. Among many proposed RNA control preparations (4)(5), armored RNA is currently the most suitable for clinical applications as it carries the viral RNA target of interest in a form that is ribonuclease-resistant, noninfectious, and stable after prolonged incubation in clinical matrices, and the preparations are substantially less expensive to manufacture than virusinfected plasma (6)(7)(8). Thus, armored RNA has been applied as a positive control for a variety of RNA viruses (9). Because most commercial armored RNA preparations contain exogenous sequences of <500 nucleotides (9), separate armored RNA …

High resolution melting analysis of the MMAA gene in patients with cblA and in those with undiagnosed methylmalonic aciduria

The gene product of MMAA is required for the intracellular metabolism of cobalamin (Cbl). Mutations in this gene lead to the cblA class of disorders, characterized by isolated methylmalonic aciduria. We have been concerned that somatic cell methods of diagnosis may miss patients with mild cellular phenotypes. A high resolution melting analysis (HRMA) assay was developed to rapidly scan the coding exons and flanking intronic regions of the MMAA gene for variants. DNA was scanned by HRMA from 96 unaffected reference individuals, 72 cblA patients confirmed by complementation, and 181 patients with isolated elevated methylmalonic acid, who could not be diagnosed using complementation analysis. Suspected variants were confirmed by Sanger sequencing. In the cblA cohort, HRMA correctly identified all previously known mutations as well as an additional 22 variants, 10 of which had not been previously reported. Novel variants included one duplication (c.551dupG, p.C187LfsX3), one deletion (c.387delC, p.Y129YfsX13), one splice site mutation (c.440-2A>G, splice site), 4 missense mutations (c.748G>A, p.E520K; c.820G>A, p.G274S; c.627G>T, p.R209S; c.826A>G, p.K276E), and 3 nonsense mutations (c.960G>A, p.W320X; c.1075C>T, p.E359X; c.1084C>T, p.Q362X). All novel missense variants affect highly conserved residues and are predicted to be damaging. Scanning of MMAA in the 181 undiagnosed samples revealed a single novel heterozygous missense change (c.821G>A, p.G274D).

Rapid detection of non-deletional mutations causing α-thalassemia by multicolor melting curve analysis.

Abstract Background: α-Thalassemia, caused by mutations in the α-globin genes, is one of the most common monogenic inherited disorders in the world. However, non-deletional α-thalassemia mutations remain undetected in routine clinical testing due to the lack of a suitable method. In this study, a closed- and single-tube assay for the detection of six common non-deletional α-thalassemia mutations in the HBA2 gene was developed based on multicolor melting curve analysis. Methods: The assay consisted of one pair of primers specific for the HBA2 gene and four dual-labeled, self-quenched probes targeting six non-deletional α-thalassemia mutations. The sensitivity, reproducibility, and accuracy of the method were validated via 700 genomic DNA samples. Results: The assay had a reproducibility of 100%, could detect gDNA of different genotype as low as 1 ng per reaction, and had an overall accuracy of 100% when compared with RDB analysis and Sanger sequencing. Conclusions: The developed assay is rapid, robust, and cost-effective while maintaining high sensitivity, specificity, and throughput.

Simultaneous Genotyping of α-Thalassemia Deletional and Nondeletional Mutations by Real-Time PCR–Based Multicolor Melting Curve Analysis

α-Thalassemia, which is caused by defective synthesis of the hemoglobin α-globin chains, is the most commonly inherited recessive hemoglobin abnormality. Genetic detection of a defective α-globin gene is challenging because of a variety of large deletions of the α-globin gene cluster and nondeletional mutations. Separate detections of them are often required using complex and error-prone open-tube methods. We report a novel real-time PCR-based assay that can simultaneously genotype four major deletional and three common nondeletional mutations in two parallel reactions by using multicolor melting curve analysis. The turnaround time of this closed-tube assay was within 3.5 hours, the limit of detection was 5 ng of human genomic DNA per reaction, and as low as 5% mutant DNA could be detected in the mosaic samples. The assay was evaluated using 1213 precharacterized genomic DNA samples in a double-blind manner. All seven α-thalassemia mutations were accurately genotyped, yielding a 99.3% concordance with the comparison assays. The 14 discordant samples contained the HKαα allele that was undetected by the traditional methods. Considering its rapidity, ease of use, and accuracy, we concluded that our real-time PCR assay may be recommended as an alternative screening and diagnostic tool for α-thalassemia.

Rapid detection of G6PD mutations by multicolor melting curve analysis

The MeltPro G6PD assay is the first commercial genetic test for glucose-6-phosphate dehydrogenase (G6PD) deficiency. This multicolor melting curve analysis-based real-time PCR assay is designed to genotype 16 G6PD mutations prevalent in the Chinese population. We comprehensively evaluated both the analytical and clinical performances of this assay. All 16 mutations were accurately genotyped, and the standard deviation of the measured Tm was <0.3°C. The limit of detection was 1.0ng/μL human genomic DNA. The assay could be run on four mainstream models of real-time PCR machines. The shortest running time (150min) was obtained with LightCycler 480 II. A clinical study using 763 samples collected from three hospitals indicated that, of 433 samples with reduced G6PD activity, the MeltPro assay identified 423 samples as mutant, yielding a clinical sensitivity of 97.7% (423/433). Of the 117 male samples with normal G6PD activity, the MeltPro assay confirmed that 116 samples were wild type, yielding a clinical specificity of 99.1% (116/117). Moreover, the MeltPro assay demonstrated 100% concordance with DNA sequencing for all targeted mutations. We concluded that the MeltPro G6PD assay is useful as a diagnostic or screening tool for G6PD deficiency in clinical settings.