Approach For Mutation Detection Research Articles

Development of a gLCR-based KRAS mutation detection approach and its comparison with other screening methods.

A gapped ligase chain reaction (gLCR)-based technique was developed and tested on clinical formalin-fixed, paraffin-embedded (FFPE) tissues from colorectal cancer patients. The technique was designed to detect low-level KRAS codon 12 or 13 mutations or confirming doubtful results gained by less sensitive KRAS screening techniques. The gLCR approach was compared with mutation screening techniques commonly used in routine diagnostics regarding sensitivity and specificity. The herein described monoplex gLCR technique is a useful and powerful tool for detecting low-level KRAS codon 12 and 13 mutations in a vast majority of wild type DNA. The gLCR has the capacity to detect one mutated allele in an excess of at least one million wild type alleles (0.0001 %) and is therefore an ideal technique for confirming doubtful KRAS mutation screening results obtained by other techniques. The variance of the gLCRs signal amplitude was very low and is showing a high reproducibility with constant sensitivity even at higher dilutions. The financial effort and the handling time for this technique are low and comparable to a standard cycle sequencing reaction. Additionally, the gLCR technique is easy extendable for the detection of many other clinical relevant mutation hotspots.

Preimplantation genetic diagnosis using combined strategies on a breast cancer patient with a novel genomic deletion in BRCA2.

To perform Preimplantation Genetic Diagnosis (PGD) on a paternal Brca2 unknown mutation carrier with early-onset breast cancer, whose paternal grandmother and mother had breast cancer at 60s. Elucidating the linkage via single sperm haplotyping on patient's carrier brother, and identifying the genomic deletion via BLAST followed by PCR screening. PGD was subsequently conducted. The mutant allele was found by using 4 microsatellite and 2 intragenic SNP markers. Recombination was detected in 8% of sperms. BLAST was utilized to locate putative hairpin structure(s), followed by PCR screening with seven sets of primers. A novel 2,596 bp deletion containing exon 15 ~ 16 was identified. Due to the severity of phenotype and the integrity of exon 11 encoding RAD51 binding domain, and the fact that the patient's mother also had breast cancer at her 60s, we speculate a possible coexistence of maternal breast cancer risk allele(s). Embryo biopsy was performed on day 3. Unaffected morula and blastocyst were replaced on day 5, resulting in a singleton livebirth. A breast lump appeared in the patient after delivery without the presence of malignant cells. Concerning the assisted reproductive option for breast cancer patients, the possibility of coexistence of multiple familial risk alleles and the significance of each mutation to the phenotype should be evaluated. To eliminate misdiagnosis resulting from recombination and/or allelic drop-out, both direct mutation detection and linkage analysis approaches may be necessary. BLAST is a very useful and cost-effective tool for identifying large genomic deletion.

Next-generation sequencing: a change of paradigm in molecular diagnostic validation.

Next-generation sequencing (NGS) is beginning to show its full potential for diagnostic and therapeutic applications. In particular, it is enunciating its capacity to contribute to a molecular taxonomy of cancer, to be used as a standard approach for diagnostic mutation detection, and to open new treatment options that are not exclusively organ-specific. If this is the case, how much validation is necessary and what should be the validation strategy, when bringing NGS into the diagnostic/clinical practice? This validation strategy should address key issues such as: what is the overall extent of the validation? Should essential indicators of test performance such as sensitivity of specificity be calculated for every target or sample type? Should bioinformatic interpretation approaches be validated with the same rigour? What is a competitive clinical turnaround time for a NGS-based test, and when does it become a cost-effective testing proposition? While we address these and other related topics in this commentary, we also suggest that a single set of international guidelines for the validation and use of NGS technology in routine diagnostics may allow us all to make a much more effective use of resources.

Identification of copy number variants from exome sequence data.

BackgroundWith advances in next generation sequencing technologies and genomic capture techniques, exome sequencing has become a cost-effective approach for mutation detection in genetic diseases. However, computational prediction of copy number variants (CNVs) from exome sequence data is a challenging task. Whilst numerous programs are available, they have different sensitivities, and have low sensitivity to detect smaller CNVs (1–4 exons). Additionally, exonic CNV discovery using standard aCGH has limitations due to the low probe density over exonic regions. The goal of our study was to develop a protocol to detect exonic CNVs (including shorter CNVs that cover 1–4 exons), combining computational prediction algorithms and a high-resolution custom CGH array.ResultsWe used six published CNV prediction programs (ExomeCNV, CONTRA, ExomeCopy, ExomeDepth, CoNIFER, XHMM) and an in-house modification to ExomeCopy and ExomeDepth (ExCopyDepth) for computational CNV prediction on 30 exomes from the 1000 genomes project and 9 exomes from primary immunodeficiency patients. CNV predictions were tested using a custom CGH array designed to capture all exons (exaCGH). After this validation, we next evaluated the computational prediction of shorter CNVs. ExomeCopy and the in-house modified algorithm, ExCopyDepth, showed the highest capability in detecting shorter CNVs. Finally, the performance of each computational program was assessed by calculating the sensitivity and false positive rate.ConclusionsIn this paper, we assessed the ability of 6 computational programs to predict CNVs, focussing on short (1–4 exon) CNVs. We also tested these predictions using a custom array targeting exons. Based on these results, we propose a protocol to identify and confirm shorter exonic CNVs combining computational prediction algorithms and custom aCGH experiments.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-661) contains supplementary material, which is available to authorized users.

A gradient-boosting approach for filtering de novo mutations in parent–offspring trios

Whole-genome and -exome sequencing on parent-offspring trios is a powerful approach to identifying disease-associated genes by detecting de novo mutations in patients. Accurate detection of de novo mutations from sequencing data is a critical step in trio-based genetic studies. Existing bioinformatic approaches usually yield high error rates due to sequencing artifacts and alignment issues, which may either miss true de novo mutations or call too many false ones, making downstream validation and analysis difficult. In particular, current approaches have much worse specificity than sensitivity, and developing effective filters to discriminate genuine from spurious de novo mutations remains an unsolved challenge. In this article, we curated 59 sequence features in whole genome and exome alignment context which are considered to be relevant to discriminating true de novo mutations from artifacts, and then employed a machine-learning approach to classify candidates as true or false de novo mutations. Specifically, we built a classifier, named De Novo Mutation Filter (DNMFilter), using gradient boosting as the classification algorithm. We built the training set using experimentally validated true and false de novo mutations as well as collected false de novo mutations from an in-house large-scale exome-sequencing project. We evaluated DNMFilter's theoretical performance and investigated relative importance of different sequence features on the classification accuracy. Finally, we applied DNMFilter on our in-house whole exome trios and one CEU trio from the 1000 Genomes Project and found that DNMFilter could be coupled with commonly used de novo mutation detection approaches as an effective filtering approach to significantly reduce false discovery rate without sacrificing sensitivity. The software DNMFilter implemented using a combination of Java and R is freely available from the website at http://humangenome.duke.edu/software.

Molecular profiling of cholangiocarcinoma shows potential for targeted therapy treatment decisions

Cholangiocarcinoma is a highly lethal cancer of the biliary tract. The intrahepatic subtype of cholangiocarcinoma is increasing in incidence globally. Despite technologic advancements over the past decade, little is known about the somatic changes that occur in these tumors. The goal of this study was to determine the frequency of common oncogenes in resected cholangiocarcinoma specimens that could provide potential therapeutic targets for patients diagnosed with cholangiocarcinoma. Formalin-fixed, paraffin-embedded tissue blocks from 94 resected cholangiocarcinomas were used to extract DNA from areas comprising more than 20% tumor. Specimens were evaluated using the Sequenom MassARRAY OncoCarta Mutation Profiler Panel (San Diego, CA). This matrix-assisted laser desorption/ionization-time of flight mass spectrometry single genotyping panel evaluates 19 oncogenes for 238 somatic mutations. Twenty-five mutations were identified in 23 of the 94 cholangiocarcinomas within the following oncogenes: KRAS (n = 12), PIK3CA (n = 5), MET (n = 4), EGFR (n = 1), BRAF (n = 2), and NRAS (n = 1). Mutations were identified in 7 (26%) of 27 extrahepatic cholangiocarcinomas and 16 (24%) of 67 intrahepatic cholangiocarcinomas. When combined with IDH1/2 testing, 40 (43%) of the 94 cholangiocarcinomas had a detectable mutation. MassARRAY technology can be used to detect mutations in a wide variety of oncogenes using paraffin-embedded tissue. Clinical testing for somatic mutations may drive personalized therapy selection for cholangiocarcinomas in the future. The variety of mutations detected suggests that a multiplexed mutation detection approach may be necessary for managing patients with biliary tract malignancy.

Multi-Purpose Utility of Circulating Plasma DNA Testing in Patients with Advanced Cancers

Tumor genomic instability and selective treatment pressures result in clonal disease evolution; molecular stratification for molecularly targeted drug administration requires repeated access to tumor DNA. We hypothesized that circulating plasma DNA (cpDNA) in advanced cancer patients is largely derived from tumor, has prognostic utility, and can be utilized for multiplex tumor mutation sequencing when repeat biopsy is not feasible. We utilized the Sequenom MassArray System and OncoCarta panel for somatic mutation profiling. Matched samples, acquired from the same patient but at different time points were evaluated; these comprised formalin-fixed paraffin-embedded (FFPE) archival tumor tissue (primary and/or metastatic) and cpDNA. The feasibility, sensitivity, and specificity of this high-throughput, multiplex mutation detection approach was tested utilizing specimens acquired from 105 patients with solid tumors referred for participation in Phase I trials of molecularly targeted drugs. The median cpDNA concentration was 17 ng/ml (range: 0.5–1600); this was 3-fold higher than in healthy volunteers. Moreover, higher cpDNA concentrations associated with worse overall survival; there was an overall survival (OS) hazard ratio of 2.4 (95% CI 1.4, 4.2) for each 10-fold increase in cpDNA concentration and in multivariate analyses, cpDNA concentration, albumin, and performance status remained independent predictors of OS. These data suggest that plasma DNA in these cancer patients is largely derived from tumor. We also observed high detection concordance for critical ‘hot-spot’ mutations (KRAS, BRAF, PIK3CA) in matched cpDNA and archival tumor tissue, and important differences between archival tumor and cpDNA. This multiplex sequencing assay can be utilized to detect somatic mutations from plasma in advanced cancer patients, when safe repeat tumor biopsy is not feasible and genomic analysis of archival tumor is deemed insufficient. Overall, circulating nucleic acid biomarker studies have clinically important multi-purpose utility in advanced cancer patients and further studies to pursue their incorporation into the standard of care are warranted.

Electrochemical detection of point mutation based on surface hybridization assay conjugated allele-specific polymerase chainreaction

In this work, we developed an electrochemical detection method based on allele-specific polymerase chain reaction (AS-PCR) and surface hybridization assay technique for the point mutation detection. A high-fidelity VentR™(exo−) DNA polymerase, which eliminated the 3′→5′ proofreading exonuclease activity by genetical engineering, was used to discriminate and extend the detection probe that perfectly matched with mutant target DNA and generate a redox-active DNA replica which folded into a molecular beacon structure by intramolecular hybridization. After hybridized with capture probe modified on gold electrode by self-assembly reaction, the redox tags can be closed to electrode, resulting in a substantial current with the maximized sensitivity for point mutation analysis. However, when there is an allele mismatch in the wild target DNA, and so no the redox-active replica DNA can be obtained. In this case, no remarkable current signal can be trigged. The proposed approach has been successfully implemented for the identification of single base mutation at the −28 position in human β-globin gene with a detection limit of 0.5fM, demonstrating that this method provides a highly specific, sensitive and cost-efficient approach for point mutation detection.

Autosomal dominant polycystic kidney disease: Comprehensive mutation analysis of PKD1 and PKD2 in 700 unrelated patients

Autosomal dominant polycystic kidney disease (ADPKD), the most common inherited kidney disorder, is caused by mutations in PKD1 or PKD2. The molecular diagnosis of ADPKD is complicated by extensive allelic heterogeneity and particularly by the presence of six highly homologous sequences of PKD1 exons 1-33. Here, we screened PKD1 and PKD2 for both conventional mutations and gross genomic rearrangements in up to 700 unrelated ADPKD patients--the largest patient cohort to date--by means of direct sequencing, followed by quantitative fluorescent multiplex polymerase chain reaction or array-comparative genomic hybridization. This resulted in the identification of the largest number of new pathogenic mutations (n = 351) in a single publication, expanded the spectrum of known ADPKD pathogenic mutations by 41.8% for PKD1 and by 23.8% for PKD2, and provided new insights into several issues, such as the population-dependent distribution of recurrent mutations compared with founder mutations and the relative paucity of pathogenic missense mutations in the PKD2 gene. Our study, together with others, highlights the importance of developing novel approaches for both mutation detection and functional validation of nondefinite pathogenic mutations to increase the diagnostic value of molecular testing for ADPKD.

Comparative analysis of CE‐SSCP to standard RFLP‐CE‐FLA method in quantification of known viral variants within an RNA virus quasispecies

RNA viruses display the highest replication error rate in our biosphere, leading to highly diverse viral populations termed quasispecies. The gold standard method for detection and quantification of variants in a quasispecies is cloning and sequencing, but it is expensive, laborious and time consuming. Therefore, other mutation detection approaches, including SSCP, are often used. In this study, we demonstrate development and the usage of a CE-SSCP method for quantification of two nearly identical viral variants in heterogenic population of a mumps virus strain and its comparison to RFLP-CE-fragment length analysis (RFLP-CE-FLA). Analyzed PCR fragments were of the same size (245 bp) with one difference in their nucleotide sequence. The limit of detection of both methods was at 5% of the minor variant. When PCR amplicons of the two variants were pooled, methods' results were very similar. On the contrary, the quantification results of samples in which variants were mixed prior to PCR showed substantial difference between the two methods. Our results indicate that although both methods can be used for detection and monitoring of a specific mutation within a viral population, caution should be taken when quantitative analysis of complex samples is based solely on results of one method.

Benchmarking of Mutation Diagnostics in Clinical Lung Cancer Specimens

Treatment of EGFR-mutant non-small cell lung cancer patients with the tyrosine kinase inhibitors erlotinib or gefitinib results in high response rates and prolonged progression-free survival. Despite the development of sensitive mutation detection approaches, a thorough validation of these in a clinical setting has so far been lacking. We performed, in a clinical setting, a systematic validation of dideoxy ‘Sanger’ sequencing and pyrosequencing against massively parallel sequencing as one of the most sensitive mutation detection technologies available. Mutational annotation of clinical lung tumor samples revealed that of all patients with a confirmed response to EGFR inhibition, only massively parallel sequencing detected all relevant mutations. By contrast, dideoxy sequencing missed four responders and pyrosequencing missed two responders, indicating a dramatic lack of sensitivity of dideoxy sequencing, which is widely applied for this purpose. Furthermore, precise quantification of mutant alleles revealed a low correlation (r2 = 0.27) of histopathological estimates of tumor content and frequency of mutant alleles, thereby questioning the use of histopathology for stratification of specimens for individual analytical procedures. Our results suggest that enhanced analytical sensitivity is critically required to correctly identify patients responding to EGFR inhibition. More broadly, our results emphasize the need for thorough evaluation of all mutation detection approaches against massively parallel sequencing as a prerequisite for any clinical implementation.

A fast, cost‐efficient and sensitive approach for KRAS mutation detection using multiplexed primer extension with IP/RP‐HPLC separation

Mutations in the KRAS gene are very important diagnostic and prognostic markers in cancer. Particularly, KRAS mutations at codons 12 and 13 have a high prognostic value for EGFR-directed antibody therapies. Several methods are available to detect the most common mutations, some of them are commercialized. The most frequently used techniques, allele-specific PCR or direct sequencing, are not standardized and often lack sensitivity to detect low amounts of mutated tumor cells in paraffin-embedded tissue-blocks leading to a high number of false-negatives. Here we present a reliable, fast, cost-effective and sensitive approach for KRAS mutation detection that has a high potential for standardized large scale screening. The method is based on multiplexed primer extension reactions coupled to HPLC separation. The highly sensitive assay gives easily interpretable and reproducible results at affordable costs. We describe the method and an application example for diagnosis in early colorectal cancer screening.

High-sensitive electrochemical detection of point mutation based on polymerization-induced enzymatic amplification

Here a highly sensitive electrochemical method is described for the detection of point mutation in DNA. Polymerization extension reaction is applied to specifically initiate enzymatic electrochemical amplification to improve the sensitivity and enhance the performance of point mutation detection. In this work, 5′-thiolated DNA probe sequences complementary to the wild target DNA are assembled on the gold electrode. In the presence of wild target DNA, the probe is extended by DNA polymerase over the free segment of target as the template. After washing with NaOH solution, the target DNA is removed while the elongated probe sequence remains on the sensing surface. Via hybridizing to the designed biotin-labeled detection probe, the extended sequence is capable of capturing detection probe. After introducing streptavidin-conjugated alkaline phosphatase (SA-ALP), the specific binding between streptavidin and biotin mediates a catalytic reaction of ascorbic acid 2-phosphate (AA-P) substrate to produce a reducing agent ascorbic acid (AA). Then the silver ions in solution are reduced by AA, leading to the deposition of silver metal onto the electrode surface. The amount of deposited silver which is determined by the amount of wild target can be quantified by the linear sweep voltammetry (LSV). The present approach proved to be capable of detecting the wild target DNA down to a detection limit of 1.0 × 10 −14 M in a wide target concentration range and identifying −28 site (A to G) of the β-thalassemia gene, demonstrating that this scheme offers a highly sensitive and specific approach for point mutation detection.

Rapid Identification of Common β-Thalassemia Mutations in the Chinese Population Using Duplex or Triplex Amplicon Genotyping by High-Resolution Melting Analysis

β-Thalassemia is one of the most prevalent inherited diseases in China. To date, over 20 β-thalassemia mutations have been identified in the Chinese population, and four mutations [CD41-42 (-4 bp), IVS-2-654C→T, CD17A→T, and -28A→G] account for approximately 90% of the cases. Therefore, the exploration of simple, reliable, and rapid approaches for molecular detection of these common mutations is important for prevention and early diagnosis of the disease. High-resolution melting (HRM) analysis is a new technique for mutation detection that has the advantages of rapidity, accuracy, and convenience. Building on one-amplicon genotyping by HRM analysis, we developed duplex and triplex amplicon genotyping to simultaneously identify these common β-thalassemia mutations in patients or carriers. Two or three sets of primers were combined to conduct duplex or triplex amplicon genotyping, which distinguished a variety of genotypes by HRM based on the melting curve shapes. Seventy-one DNA samples from β-thalassemia traits or patients were analyzed using the described approaches and 65 were identified to carry the 4 common β-thalassemia alleles including 56 heterozygous mutations [23 for CD41-42 (-4 bp), 18 for IVS-2-654C→T, 11 for CD17A→T, and 4 for -28A→G], 3 homozygous mutations for IVS-2-654C→T, and 6 compound heterozygous mutations [CD41-42 (-4 bp)/IVS-2-654C→T (4 cases), -28A→G/CD17A→T (1 case), IVS-2-654C→T/CD17A→T (1 case)]. The whole procedure for mutation detection was completed within only half an hour. The results derived from HRM analysis were fully in accordance with sequencing. We suggest this rapid and accurate method for molecular screening to detect the common β-thalassemia mutations in the Chinese population as well as in other ethnic groups and nationalities in which the above four β-thalassemia alleles are prevalent.

A validated algorithm for sensitive and cost-effective mutation detection in clinical cancer specimens.

e12009 Background: Patients with EGFR-mutant lung cancer experience tumor shrinkage and prolonged survival when treated with EGFR inhibitors. Furthermore, drugs targeting additional mutational activated proto-oncogenes are currently being evaluated clinically. Thus, validated approaches for sensitive and accurate mutation detection in a clinical setting are urgently needed but have, so far, been lacking. Methods: Here, we performed a careful and systematic validation of two sequencing approaches (namely, Sanger sequencing and pyrosequencing) against the gold standard, massively parallel sequencing. Results: Prospective mutational annotation of clinical lung tumor samples as a function of tumor content revealed previously recognized limitations of Sanger sequencing but also indicated that pyrosequencing is a reliable and sensitive approach to mutation detection in the setting of limited tumor content. Importantly, pyrosequencing is highly cost effective and dramatically extends the fraction of tumors that can be analyzed without the need for costly massively parallel sequencing. Furthermore, we identified severe limitations of histopathological estimates of tumor content, thus supporting the application of sensitive mutation detection approaches as apposed to microdissection of cancer specimens. Conclusions: In summary, we have established an analytical algorithm for mutation detection in an everyday clinical setting, taking into account quality and type of tumor specimens, tumor content as well as sensitivity, feasibility and costs of appropriate sequencing assays. Furthermore, we suggest thorough evaluation of all mutation detection approaches against massively parallel sequencing as a prerequisite for any clinical implementation. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Roche, Sequenom Boehringer Ingelheim, Infinity, Roche AstraZeneca

Magnetic beads based rolling circle amplification–electrochemiluminescence assay for highly sensitive detection of point mutation

The identification of point mutations is particularly essential in the fields of medical diagnosis and prognosis of many pathogenic and genetic diseases. In this study, an rolling circle amplification (RCA) based electrochemiluminescence (ECL) assay for highly sensitive point mutation detection was developed. In the assay, an allele-discriminating padlock probe was designed for targeting the sequence in the p53 oncogene locus. A circular template generated by enzymatic ligation upon the recognition of a point mutation (CGT to CAT) on the oncogene could be amplified isothermally by Phi29 DNA polymerase. The elongated products, containing hundreds of copies of the circular DNA template sequence, were hybridized with Ru(bpy)32+ (TBR)-tagged probes and then captured onto streptavidin-coated paramagnetic beads. The resulting products were analyzed by magnetic bead based ECL platform. As low as 2amol of mutated strands was detected by this assay, which could be attributed to the high amplification efficiency of Phi29 DNA polymerase and current magnetic bead based ECL detection platform. In addition, the positive mutation detection was achieved with a wild-type to mutant ratio of 10000:1, due to the high fidelity of DNA ligase in differentiating mismatched bases at the ligation site. It is demonstrated that this proposed method provides a highly sensitive and specific approach for point mutation detection.

Mutation discovery in the mouse using genetically guided array capture and resequencing

Forward genetics (phenotype-driven approaches) remain the primary source for allelic variants in the mouse. Unfortunately, the gap between observable phenotype and causative genotype limits the widespread use of spontaneous and induced mouse mutants. As alternatives to traditional positional cloning and mutation detection approaches, sequence capture and next-generation sequencing technologies can be used to rapidly sequence subsets of the genome. Application of these technologies to mutation detection efforts in the mouse has the potential to significantly reduce the time and resources required for mutation identification by abrogating the need for high-resolution genetic mapping, long-range PCR, and sequencing of individual PCR amplimers. As proof of principle, we used array-based sequence capture and pyrosequencing to sequence an allelic series from the classically defined Kit locus (approximately 200 kb) from each of five noncomplementing Kit mutants (one known allele and four unknown alleles) and have successfully identified and validated a nonsynonymous coding mutation for each allele. These data represent the first documentation and validation that these new technologies can be used to efficiently discover causative mutations. Importantly, these data also provide a specific methodological foundation for the development of large-scale mutation detection efforts in the laboratory mouse.

A novel mutant allele specific amplification and electrochemiluminescence method for the detection of point mutation in clinical samples

A novel mutant allele specific amplification (MASA) and electrochemiluminescence (ECL) method for point mutation detection is proposed. Briefly, the target gene was amplified by a biotinylated mutant specific sense primer and a Ru(bpy) 3 2+ (TBR)-labeled universal antisense primer. Only the mutant allele can be selectively amplified by the mutant specific primer pair. Then, the MASA product was captured onto the streptavidinylated magnetic beads through biotin–streptavidin linkage and detected by measuring the ECL emission of TBR. The method was applied to detect a possible point mutation at codon 12 of K-ras oncogene in 30 colorectal cancer (CAC) clinical samples. The experimental results show that the method can detect K-ras mutant in a 5000-fold excess of wild-type allele. Furthermore, different kinds of mutations can be clearly discriminated. The point mutation was found in 15 (50%) out of 30 CAC samples. This novel MASA–ECL method could potentially become a sensitive, specific, simple, rapid and safe approach for point mutation detection.

Rapid and sensitive detection of point mutation by DNA ligase-based electrochemiluminescence assay

The identification of single-base mutations in particular genes plays an increasingly important role in medical diagnosis and prognosis of genetic-based diseases. Here we report a new method for the analysis of point mutations in genomic DNA through the integration of allele-specific oligonucleotide ligation assay (OLA) with magnetic beads-based electrochemiluminescence (ECL) detection scheme. In this assay, the tris(bipyridine) ruthenium (TBR) labeled probe and the biotinylated probe are designed to perfectly complementary to the mutant target; thus a ligation can be generated between those two probes by Taq DNA Ligase in the presence of mutant target. If there is an allele mismatch, the ligation does not take place. The ligation products are then captured onto streptavidin-coated paramagnetic beads, and detected by measuring the ECL signal of the TBR label. Results showed that the new method held a low detection limit down to 10 fmol and was successfully applied in the identification of point mutations from ASTC-α-1 cell line, PANC-1 cell line and blood cell in codon 273 of TP53 oncogene. In summary, this method provides a sensitive, cost-effective and easy operation approach for point mutation detection.

Electrochemical scanning of DNA point mutations via MutS protein-mediated mismatch recognition

MutS protein is an important part of the DNA repair system which can specifically recognize and bind all possible single-base mismatches as well as 1–4 base insertion or deletion loops with varying affinities independent of other proteins or cofactors. In this paper, a new approach for electrochemical gene mutation detection based on the utilization of MutS protein for the mutation recognition and spontaneously intercalated methylene blue (MB) markers for electrochemical signal generation is described. This method involves the immobilization of MutS protein onto the gold electrode, the hybridization of target DNA to form homoduplex or heteroduplex DNA, the application of MutS protein for the mutation recognition, and finally the intercalation of MB. The background is very low because MutS protein binds DNA containing mispaired and unpaired bases but does not bind equally well to DNA without mismatches or single-stranded DNA. The proposed approach has been successfully implemented for the identification of single-base mutation in −28 site of the β-thalassemia gene with a detection limit of 5.6×10−13M, demonstrating that this method provides a highly specific and cost-efficient approach for point mutation detection.