Machine learning based DNA melt curve profiling enables automated novel genotype detection.

Surveillance for genetic variation of microbial pathogens, both within and among species, plays an important role in informing research, diagnostic, prevention, and treatment activities for disease control. However, large-scale systematic screening for novel genotypes remains challenging in part due to technological limitations. Towards addressing this challenge, we present an advancement in universal microbial high resolution melting (HRM) analysis that is capable of accomplishing both known genotype identification and novel genotype detection. Specifically, this novel surveillance functionality is achieved through time-series modeling of sequence-defined HRM curves, which is uniquely enabled by the large-scale melt curve datasets generated using our high-throughput digital HRM platform. Taking the detection of bacterial genotypes as a model application, we demonstrate that our algorithms accomplish an overall classification accuracy over 99.7% and perform novelty detection with a sensitivity of 0.96, specificity of 0.96 and Youden index of 0.92. Since HRM-based DNA profiling is an inexpensive and rapid technique, our results add support for the feasibility of its use in surveillance applications.

The bacterial DnaA-trio replication origin element specifies single-stranded DNA initiator binding.

DNA replication is tightly controlled to ensure accurate inheritance of genetic information. In all organisms, initiator proteins possessing AAA+ (ATPases associated with various cellular activities) domains bind replication origins to license new rounds of DNA synthesis. In bacteria the master initiator protein, DnaA, is highly conserved and has two crucial DNA binding activities. DnaA monomers recognize the replication origin (oriC) by binding double-stranded DNA sequences (DnaA-boxes); subsequently, DnaA filaments assemble and promote duplex unwinding by engaging and stretching a single DNA strand. While the specificity for duplex DnaA-boxes by DnaA has been appreciated for over 30 years, the sequence specificity for single-strand DNA binding has remained unknown. Here we identify a new indispensable bacterial replication origin element composed of a repeating trinucleotide motif that we term the DnaA-trio. We show that the function of the DnaA-trio is to stabilize DnaA filaments on a single DNA strand, thus providing essential precision to this binding mechanism. Bioinformatic analysis detects DnaA-trios in replication origins throughout the bacterial kingdom, indicating that this element is part of the core oriC structure. The discovery and characterization of the novel DnaA-trio extends our fundamental understanding of bacterial DNA replication initiation, and because of the conserved structure of AAA+ initiator proteins these findings raise the possibility of specific recognition motifs within replication origins of higher organisms.

Implementation of high-resolution melting analysis of the porcupine (PORCN) gene for molecular diagnosis of focal dermal hypoplasia: Identification of a novel mutation.

BACKGROUND: Focal dermal hypoplasia (FDH) is rare X-linked dominant disease characterized by atrophy and linear pigmentation of the skin, split hand/foot deformities and ocular anomalies. FDH is caused by mutations of the Porcupine (PORCN) gene, which encodes an enzyme that catalyzes the palmitoylation of Wnt ligands required for their secretion. High resolution melting analysis (HRM) is a technique that allows rapid, labor-efficient, low-cost detection of genomic variants. In the present study, we report the successful implementation of HRM in the molecular diagnosis of FDH. METHODS: Polymerase chain reaction and HRM assays were designed and optimized for each of the coding exons of the PORCN gene, processing genomic DNA samples form a non-affected control and a patient complying with the FDH diagnostic criteria. The causal mutation was characterized by Sanger sequencing from an amplicon showing a HRM trace suggesting heterozygous variation and was validated using an amplification-refractory mutation system (ARMS) assay. RESULTS: The melting profiles suggested the presence of a variant in the patient within exon 1. Sanger sequencing revealed a previously unknown C to T transition replacing a glutamine codon for a premature stop codon at position 28, which was validated using ARMS. CONCLUSIONS: Next-generation sequencing facilitates the molecular diagnosis of monogenic disorders; however, its cost-benefit ratio is not optimal when a single, small or medium size causal gene is already identified and the clinical diagnostic presumption is strong. Under those conditions, as it is the case for FDH, HRM represents a cost- and labor-effective approach.

A DNA Switch for Detecting Single Nucleotide Polymorphism within a Long DNA Sequence Under Denaturing Conditions.

DNA detection is usually conducted under nondenaturing conditions to favor the formation of Watson-Crick base-paring interactions. However, although such a setting is excellent for distinguishing a single-nucleotide polymorphism (SNP) within short DNA sequences (15-25 nucleotides), it does not offer a good solution to SNP detection within much longer sequences. Here we report on a new detection method capable of detecting SNP in a DNA sequence containing 35-90 nucleotides. This is achieved through incorporating into the recognition DNA sequence a previously discovered DNA molecule that forms a stable G-quadruplex in the presence of 7 molar urea, a known condition for denaturing DNA structures. The systems are configured to produce both colorimetric and fluorescent signals upon target binding.

Spliceogenic analysis of BRCA1 c.439T>C (rs794727800) variant by High Resolution Melting Analysis.

Correct classification of genomic variants causing potentially aberrant splicing is of utmost importance for patient management, especially in clinically actionable genes such as BRCA1/2. In this article, we report molecular evaluation of the BRCA1 c.439T>C (rs794727800, p.Leu147=) variant based on RNA of a patient suffering with high-grade serous ovarian cancer syndrome, to add new evidence to the only in silico data available for this variant. High Resolution Melting Analysis (HRMA) was used for the first time to investigate the spliceogenicity of a BRCA1 variant. HRMA with Sanger sequencing provided evidence that the c.439C allele does not cause aberrant splicing of the BRCA1 exon 7. In addition, HRMA with Sanger highlighted a different expression of the naturally occurring BRCA1 r.442_444del (c.442_444delCAG, p.Gln148del, at DNA level) isoform between blood and tumor, in this patient. HRMA is an alternative molecular approach to analyze spliceogenic properties of the c.439T>C variant and potentially for all those BRCA1/2 variants affecting splicing sites. These new evidences allowed to classify definitively the c.439T>C variant as benign. Furthermore, the different BRCA1 r.442_444del expression opens the discussion to consider a wider classification criteria for the splicing variants, including molecular evaluation at tissue level, which is an aspect currently scarcely considered in BRCA1/2 variant classification recommendations.

High resolution melting profiles (HRMPs) obtained by magnetic induction cycler (MIC) have been used to monitor the BRCA2 status highlighted by next generation tumor sequencing (NGTS): a combined approach in a diagnostic environment.

Resistance can be the result of secondary tissue variants (STVs), which restore the open reading frame of the germline BRCA allele, producing functional BRCA protein in germline BRCA1/2 (BRCA) pathogenic variant (PV) carriers, treated with platinum-based chemotherapy or poly-(ADP-ribose) polymerase inhibitors (PARP-1). We reported recently a BRCA2 mutant high grade serous ovarian cancer (HGSOC) patient with acquired resistance to the PARP-1 olaparib due to a STV detected by next generation tumor sequencing (NGTS). The aim of this study was to evaluate the versatility of the high-resolution melting analysis (HRMA) obtained by magnetic induction cycler (MIC) to monitor the BRCA2 status in formalin-fixed paraffin-embedded (FFPE) tissue samples of this patient and to compare the results obtained by NGTS. HRMA highlighted the BRCA2 STV previously detected in the IIIrd HGSOC recurrence following the tissue BRCA2 tissue status comparing the high resolution melting profiles (HRMPs). HRMPs differentiate not only BRCA2 alleles, but also their different allele abundance. We underline that (1) the MIC uses a latest generation technology guaranteeing temperature uniformity and maintenance in each well allowing high and accurate performance to obtain reported results and (2) the HRMA maintains a high sensitivity and specificity when it is performed on FFPE samples. Finally, this study represents an additional use of the HRMA, confirming its extreme versatility in the diagnostic environment.

Molecular identification of Candida isolates by Real-time PCR-high-resolution melting analysis and investigation of the genetic diversity of Candida species.

BACKGROUND: Candida species are considered as the cause of one of the most important opportunistic fungal diseases. Accurate identification of Candida species is important because of antifungal susceptibility patterns are different among these species, so proper identification helps in the selection of antifungal drugs for the prevention and treatment. Phenotypic methods for identification of Candida species, which are widely used in clinical microbiology laboratories, have some limitations. Real-time PCR followed by the high-resolution melting analysis (HRMA) is a novel approach for the rapid recognition of pathogenic fungi. Molecular phylogeny is essential for obtaining a better understanding of the evolution of the genus Candida and the identification of the relative degree of the Candida species. The purpose of this study was molecular identification of Candida isolates by Real-time PCR-high-resolution melting analysis and investigation of the genetic diversity of Candida species. METHODS: Two hundred and thirty-two Candida isolates including 111 Candida isolates obtained from 96 HIV/AIDS patients and 121 Candida isolates obtained from 98 non-HIV persons were identified by real-time PCR and high-resolution melting curve analysis. To evaluate genetic diversity and relationships among Candida species, PCR products of nine clinical Candida isolates, as a representative of each kind of species, were randomly selected for DNA sequence analysis. RESULTS: In HIV/AIDS patients, six species of Candida spp. were identified as follows: C albicans (n = 64; 57.7%), C glabrata (n = 31; 27.92%), C parapsilosis (n = 9; 8.1%), C tropicalis (n = 4; 3.6%), C krusei (n = 2; 1.8%), and C kefyr (n = 1; 0.90%). In non-HIV persons, we identified eight species of Candida including C albicans (n = 46; 38.33%) followed by C glabrata and C krusei (each one, n = 18; 15%), C tropicalis (n = 13; 10.83%), C lusitaniae (n = 12; 5.17%), C parapsilosis (n = 10; 4.31%), and C kefyr and C guillermondii (each one, n = 2; 1.66%). Also, the phylogenetic analysis showed the presence of two main clades and six separate subclades. Accordingly, about 88.9% of the isolates were located in clade I and 11.10% of the studied isolates were in clade II. CONCLUSIONS: Real-time PCR followed by high-resolution melting analysis (HRMA) is known as a reliable, fast, and simple approach for detection and accurate identification of Candida species, especially in clinical samples.

Detection of extended-spectrum beta-lactamase cefotaxime resistance and virulence genes in Escherichia coli by duplex quantitative real-time PCR and melt curve analysis.

Emerging virulent and antibiotic-resistant pathogens present a global public health risk. Routine monitoring of prevalence within the clinical, environmental and food production setting is vital. Quantitative real-time PCR (qPCR) coupled with melting curve analysis can rapidly and accurately characterize pathogens. We evaluated commercial qPCR mixes based on SYBR Green l and EvaGreen for developing an assay for simultaneously detecting antibiotic resistance (extended-spectrum beta-lactamase, ESBL and blaCTX-M ) and virulence (stx1, stx2 and eae) genes in Escherichia coli (n = 12) isolated from irrigation water and irrigated vegetables. SYBR Green and EvaGreen detected two amplicons (stx1 and blaCTX-M ) and (stx2 and eae) in a single reaction. A higher mean melting temperature (Tm ) separation between targeted amplicons and smoother melting curves were observed with the EvaGreen suggesting better performance when targeting multiple amplicons. Through simple stepwise optimization of DNA, cycling, primers, reaction volume and melting curve scanning rate, we adopted a conventional PCR assay for detection of large amplicons (375-1580 bp) for qPCR. This may facilitate development of cost-effective tailor-made assays for rapid and accurate monitoring of emerging foodborne and environmental pathogens in resource constrained regions.

Evaluation of the potential clinical prognostic value of lncRNA-BANCR gene in esophageal squamous cell carcinoma.

Esophageal squamous cell carcinoma (ESCC) is the seventh most common cause of cancer death in worldwide. LncRNA-BANCR is a long non-coding RNA (lncRNA), which has made new windows in cancer investigations. The aim of this survey was to determine the lncRNA-BANCR gene expression changes in patients with ESCC. In case-control investigation was performed on 150 formalin fixed-paraffin embedded tissues (75 cancerous and 75 non-cancerous tissues) of ESCC patients. The lncRNA-BANCR gene expression alteration was assessed by Real-Time PCR technique. Our findings revealed that lncRNA-BANCR gene expression was increased significantly in tumor tissues compared with the non-cancerous tissues (p = 0.0025). In addition, lncRNA-BANCR gene expression changes was positively associated with the lymph node metastasis (p = 0.013), tumor differentiation (p = 0.019) and tumor stage (p = 0.017). Our results suggest a possible role of lncRNA-BANCR in proliferation of esophageal tissues and may be considered as a potential prognostic value for ESCC metastasis.

Detection of Mutations in Mycobacterium tuberculosis pncA Gene by Modified High-Resolution Melting Curve Analysis of PCR Products.

We developed a protocol for detection of mutations in the pncA gene associated with M. tuberculosis resistance to pyrazinamide by analyzing melting curves of 7 overlapping amplicons with artificial heteroduplex formation (H-HRM) formed by co-amplification of wild-type DNA and test DNA and compared its efficiency and robustness with those of classical HRM analysis. Using HRM and H-HRM, we analyzed 35 PZAR DNA isolates carrying mutations in the pncA gene, 3 PZAR isolates without mutations in the pncA gene, and 20 PZAS isolates without mutations in the pncA gene were analyzed. The sensitivity and specificity of HRM for detection of mutations in the pncA gene were moderate: 88.57% (CI 73.26%-96.80%) and 82.61% (CI 61.22%-95.05%), respectively. The sensitivity of the H-HRM test was 97.14% (CI 85.08%-99.93%) and specificity was 95.65% (CI 78.05%-99.89%), with a significant improvement in accuracy - 96.55% vs. 93.85% for HRM. In general, despite addition stage of equalizing the concentrations of the test and control mycobacterial DNA, H-HRM showed greater stability and reproducibility at standard settings of the melting curve analysis software.

Denaturation-Enhanced Droplet Digital PCR for Liquid Biopsies.

BACKGROUND: Although interest in droplet-digital PCR technology (ddPCR) for cell-free circulating DNA (cfDNA) analysis is burgeoning, the technology is compromised by subsampling errors and the few clinical targets that can be analyzed from limited input DNA. The paucity of starting material acts as a "glass ceiling" in liquid biopsies because, irrespective how analytically sensitive ddPCR techniques are, detection limits cannot be improved past DNA input limitations. METHODS: We applied denaturation-enhanced ddPCR (dddPCR) using fragmented genomic DNA (gDNA) with defined mutations. We then tested dddPCR on cfDNA from volunteers and patients with cancer for commonly-used mutations. gDNA and cfDNA were tested with and without end repair before denaturation and digital PCR. RESULTS: By applying complete denaturation of double-stranded DNA before ddPCR droplet formation the number of positive droplets increased. dddPCR using gDNA resulted in a 1.9-2.0-fold increase in data-positive droplets, whereas dddPCR applied on highly-fragmented cfDNA resulted in a 1.6-1.7-fold increase. End repair of cfDNA before denaturation enabled cfDNA to display a 1.9-2.0-fold increase in data-positive signals, similar to gDNA. Doubling of data-positive droplets doubled the number of potential ddPCR assays that could be conducted from a given DNA input and improved ddPCR precision for cfDNA mutation detection. CONCLUSIONS: dddPCR is a simple and useful modification in ddPCR that enables extraction of more information from low-input clinical samples with minor change in protocols. It should be applicable to all ddPCR platforms for mutation detection and, potentially, for gene copy-number analysis in cancer and prenatal screening.

High-resolution melting-curve (HRM) analysis for C. meleagridis identification in stool samples.

BACKGROUND: Cryptosporidiosis represents a major public health problem. This infection, caused by a protozoan parasite of the genus Cryptosporidium, has been reported worldwide as a frequent cause of diarrhoea. In the immunocompetent host, the typical watery diarrhea can be self-limiting. However, it is severe and chronic, in the immunocompromised host and may cause death. Cryptosporidium spp. are coccidians, which complete their life cycle in both humans and animals. The two species C. hominis and C. parvum are the major cause of human infection. Compared to studies on C. hominis and C. parvum, only a few studies have developed methods to identify C. meleagridis. AIM: To develop a new real time PCR-coupled High resolution melting assay allowing the detection for C. meleagridis, in addition of the other dominant species (C. hominis and C. parvum). METHODS: The polymorphic sequence on the dihydrofolate reductase gene (DHFR) of three species was sequenced to design primers pair and establish a sensitive real-time PCR coupled to a high-resolution melting-curve (HRM) analysis method, allowing the detection of Cryptosporidium sp. and discrimination between three prevalent species in Tunisia. We analyzed a collection of 42 archived human isolates of the three studied species. RESULTS: Real-time PCR coupled to HRM assay allowed detection of Cryptosporidium, using the new designed primers, and basing on melting profile, we can distinguish C. meleagridis species in addition to C. parvum and C. hominis. CONCLUSION: We developed a qPCR-HRM assay that allows Cryptosporidium genotyping. This method is sensitive and able to distinguish three Cryptosporidium species.

Experimental platform utilising melting curve technology for detection of mutations in Mycobacterium tuberculosis isolates.

Tuberculosis (TB) remains one of the most deadly infections with approximately a quarter of cases not being identified and/or treated mainly due to a lack of resources. Rapid detection of TB or drug-resistant TB enables timely adequate treatment and is a cornerstone of effective TB management. We evaluated the analytical performance of a single-tube assay for multidrug-resistant TB (MDR-TB) on an experimental platform utilising RT-PCR and melting curve analysis that could potentially be operated as a point-of-care (PoC) test in resource-constrained settings with a high burden of TB. Firstly, we developed and evaluated the prototype MDR-TB assay using specimens extracted from well-characterised TB isolates with a variety of distinct rifampicin and isoniazid resistance conferring mutations and nontuberculous Mycobacteria (NTM) strains. Secondly, we validated the experimental platform using 98 clinical sputum samples from pulmonary TB patients collected in high MDR-TB settings. The sensitivity of the platform for TB detection in clinical specimens was 75% for smear-negative and 92.6% for smear-positive sputum samples. The sensitivity of detection for rifampicin and isoniazid resistance was 88.9 and 96.0% and specificity was 87.5 and 100%, respectively. Observed limitations in sensitivity and specificity could be resolved by adjusting the sample preparation methodology and melting curve recognition algorithm. Overall technology could be considered a promising PoC methodology especially in resource-constrained settings based on its combined accuracy, convenience, simplicity, speed, and cost characteristics.

A real time high-resolution melting PCR assay for detection and differentiation among sheep pox virus, goat pox virus, field and vaccine strains of lumpy skin disease virus.

In this paper, we report on the development of a real time high-resolution melting (HRM) PCR assay for detection and differentiation among sheep pox virus (SPPV), goat pox virus (GTPV), field isolates and vaccine strains of lumpy skin disease virus (LSDV) based on high-resolution melting curve analysis of their target PCR amplicons. A 111 bp region of LSDV010 ORF, which harbors unique genetic differences for each of these viral species, was selected as the PCR target in this study. During the validation of this assay using DNA from clinical isolates originated from naturally infected animals from the different geographic locations and reference strains, the obtained PCR amplicons demonstrated that the melting temperature picks were specific for each tested viral species, i.e., 74.56 ±â€¯0.04 °C for field LSDV, 74.95 ±â€¯0.08 °C for vaccine LSDV, 74.24 ±â€¯0.06 °C for SPPV and 73.61 ±â€¯0.04 °C for GTPV. The assessment of the assay sensitivity utilizing a LSDV field strain as a PCR template revealed the assay detection limit as low as 0.1 TCD50 lg/ml. Overall, this assay based on Rotor-Gene Q (QIAGEN) platform was shown to be reproducible across replicates and operators and can be recommended as an additional diagnostic tool to the currently available molecular assays for detection and differentiation of the genus Capripoxvirus species, including the differentiation of vaccine strains of LSDV from field isolates. The assay can be used for detection of these viruses in animal- and insect-derived field specimens.

Validation of high-resolution melting analysis as a diagnostic tool for endothelin receptor B mutation in American Paint horses and allele frequency estimation.

Overo lethal white foal syndrome (OLWFS) is a genetic disorder caused by a dinucleotide mutation in the endothelin receptor type B (EDNRB) gene leading to the death of affected foals shortly after birth. The use of rapid and reliable genetic testing is imperative for the early diagnosis of the mutation avoiding, therefore, either additional suffering or the production of affected animals. In the present study, we developed and validated a high-resolution melting (HRM) genotyping assay to detect the OLWFS causative mutation, and we also determined the frequency of heterozygotes among American Paint horses in Brazil. The HRM genotyping assay resulted in a high sensitivity, specificity, and positive and negative predictive values. The overall estimated frequency of heterozygotes was 21.6%; however, this frequency increased to 89.5% when considering only overo horses. The HRM assay optimized here was a reliable and suitable method for the detection of the dinucleotide mutation observed in the EDNRB gene resulting in a fast, accurate, and precise diagnostic tool. The causative gene mutation of OLWFS is present in heterozygosity in the American Paint Horse population in Brazil and is highly frequent among overo horses.

A novel HRM assay for differentiating classical strains and highly pathogenic strains of type 2 porcine reproductive and respiratory syndrome virus.

Differentiation of classical strains and highly pathogenic strains of porcine reproductive and respiratory syndrome virus is crucial for effective vaccination programs and epidemiological studies. We used nested PCR and high resolution melting curve analysis with unlabeled probe to distinguish between the classical and the highly pathogenic strains of this virus. Two sets of primers and a 20 bp unlabeled probe were designed from the NSP3 gene. The unlabeled probe included two mutations specific for the classical and highly pathogenic strains of the virus. An additional primer set from the NSP2 gene of the highly pathogenic vaccine strain JXA1-R was used to detect its exclusive single nucleotide polymorphism. We tested 107 clinical samples, 21 clinical samples were positive for PRRSV (consistent with conventional PCR assay), among them four were positive for the classical strain with the remainder 17 for the highly pathogenic strain. Around 10 °C difference between probe melting temperatures showed the high discriminatory power of this method. Among highly pathogenic positive samples, three samples were determined as positive for JXA1-R vaccine-related strain with a 95% genotype confidence percentage. All these genotyping results using the high resolution melting curve assay were confirmed with DNA sequencing. This unlabeled probe method provides an alternative means to differentiate the classical strains from the highly pathogenic porcine reproductive and respiratory syndrome virus strains rapidly and accurately.

Development and Validation of a High-Resolution Melting Assay To Detect Azole Resistance in Aspergillus fumigatus.

The global emergence of azole-resistant Aspergillus fumigatus strains is a growing public health concern. Different patterns of azole resistance are linked to mutations in cyp51A Therefore, accurate characterization of the mechanisms underlying azole resistance is critical to guide selection of the most appropriate antifungal agent for patients with aspergillosis. This study describes a new sequencing-free molecular screening tool for early detection of the most frequent mutations known to be associated with azole resistance in A. fumigatus PCRs targeting cyp51A mutations at positions G54, Y121, G448, and M220 and targeting different tandem repeats (TRs) in the promoter region were designed. All PCRs were performed simultaneously, using the same cycling conditions. Amplicons were then distinguished using a high-resolution melting assay. For standardization, 30 well-characterized azole-resistant A. fumigatus strains were used, yielding melting curve clusters for different resistance mechanisms for each target and allowing detection of the most frequent azole resistance mutations, i.e., G54E, G54V, G54R, G54W, Y121F, M220V, M220I, M220T, M220K, and G448S, and the tandem repeats TR34, TR46, and TR53 Validation of the method was performed using a blind panel of 80 A. fumigatus azole-susceptible or azole-resistant strains. All strains included in the blind panel were properly classified as susceptible or resistant with the developed method. The implementation of this screening method can reduce the time needed for the detection of azole-resistant A. fumigatus isolates and therefore facilitate selection of the best antifungal therapy in patients with aspergillosis.

Real-Time PCR Identification of Six Malassezia Species.

Lipophilic yeast Malassezia species is widely found on the skin surface of humans and other animals. This fungus can cause pityriasis versicolor, Malassezia folliculitis, and seborrheic dermatitis. Still now, there is a problem with species identification of Malassezia with conventional methods. We developed a real-time polymerase chain reaction (PCR) assay with multiple hybridization probes for detecting M. globosa, M. furfur, M. restricta, M. sympodialis, M. slooffiae, and M. pachydermatis. The amplification curves and specific melting peaks of the probes hybridized with real-time PCR product were used for species identifications. The assay was further evaluated on 120 samples which were performed by swabbing from 60 domestic animals (23 goats, 10 dogs, 15 cows, 3 cats, 8 rabbits, and 1 donkey) and in 70 human samples (28 patients with pityriasis versicolor, 17 breeders, and 25 control group). Fifteen M. pachydermatis were identified from animals. From human, 61 isolates were identified as M. globosa (28), M. furfur (15), M. restricta (6), M. sympodialis (8), M. slooffiae (2), and M. pachydermatis (2). Eight cases of co-detection from 6 patients and 2 breeders were revealed. Our findings show that the assay was highly effective in identifying Malassezia species. The application of multiplex real-time PCR provides a sensitive and rapid identification system for Malassezia species, which may be applied in further epidemiological surveys from clinical samples.

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.

Scanning for α-Hemoglobin Variants by High-Resolution Melting Analysis.

BACKGROUND: Definitive detection of hemoglobin (Hb) variants requires DNA sequencing. High-resolution melting (HRM) analysis of polymerase chain reaction (PCR) amplicons was applied to detect and discriminate among uncommon α-Hb variants found in Thailand. METHODS: Uncommon suspected α-Hb variants observed in Hb typing were identified by sequencing of DNA from whole blood samples. Three pairs of PCR primers covering the mutation regions in the three α-globin exons then were used for PCR coupled with difference in HRM analysis to subtract out the concomitant melting profile of the normal allele in the heterozygous state. RESULTS: DNA sequencing identified six heterozygous α-Hb variants, namely, Hb G-Waimanalo (HBA2: exon 2, codon 64 G>A), Hb J-Buda (HBA1: exon 2, codon 61 G>T), Hb Kurosaki (HBA2: exon 1; codon 7 A>G), Hb O-Indonesia (HBA1: exon 3 codon 116 G>A), Hb Q-India (HBA1:exon 2, codon 64 G>C), and Hb Q-Thailand (HBA1: exon 2 codon 74 G>C). Difference HRM analysis showed one temperature melting profile using exon 1 primer pair, four different profiles with exon 2 primer pair, and one profile with exon 3 primer pair. CONCLUSIONS: PCR-HRM analysis was effective in detecting and discriminating among single point mutations causing six uncommon α-Hb variants in heterozygous individuals. The method can be applied for routine screening due to its simplicity and relatively low cost.