The Journal of Molecular Diagnostics

Visual Automated Fluorescence Electrophoresis Provides Simultaneous Quality, Quantity, and Molecular Weight Spectra for Genomic DNA from Archived Neonatal Blood Spots

2013-03-20

The Guthrie 903 card archived dried blood spots (DBSs) are a unique but terminal resource amenable for individual and population-wide genomic profiling. The limited amounts of DBS-derived genomic DNA (gDNA) can be whole genome amplified, producing sufficient gDNA for genomic applications, albeit with variable success; optimizing the isolation of high-quality DNA from these finite, low-yield specimens is essential. Agarose gel electrophoresis and spectrophotometry are established postextraction quality control (QC) methods but lack the power to disclose detailed structural, qualitative, or quantitative aspects that underlie gDNA failure in downstream applications. Visual automated fluorescence electrophoresis (VAFE) is a novel QC technology that affords precise quality, quantity, and molecular weight of double-stranded DNA from a single microliter of sample. We extracted DNA from 3-mm DBSs archived in the Swedish Neonatal Repository for >30 years and performed the first quantitative and qualitative analyses of DBS-derived DNA on VAFE, before and after whole genome amplified, in parallel with traditional QC methods. The VAFE QC data were correlated with subsequent sample performance in PCR, sequencing, and high-density comparative genome hybridization array. We observed improved standardization of nucleic acid quantity, quality and integrity, and high performance in the downstream genomic technologies. Addition of VAFE measures in QC increases confidence in the validity of genetic data and allows cost-effective downstream analysis of gDNA for investigational and diagnostic applications.

Rapid Detection of TEM-Type Extended-Spectrum β-Lactamase (ESBL) Mutations Using Lights-On/Lights-Off Probes with Single-Stranded DNA Amplification

2013-03-20

Rapid identification of specific TEM-type β-lactamase genes in bacterial infections is important for determining appropriate clinical treatment. We report here the design and initial testing of a molecular diagnostic assay capable of amplifying a large segment of the blaTEM gene, as well as detecting widely spaced extended-spectrum β-lactamase (ESBL) mutations and inhibitor-resistant TEM (IRT) mutations (eg, clavulanic acid resistance). Single-stranded DNA is generated using linear-after-the-exponential PCR (LATE-PCR) and is analyzed at the endpoint, using a set of four fluorescently labeled and four quencher-labeled probes in a single closed tube. These lights-on/lights-off probes work in concert to generate sequence-specific fluorescence contours over a temperature range from 25°C to 75°C. Mutant sequences from synthetic TEM gene variants and from TEM gene variants in bacterial strains generated large increases in fluorescent signal relative to that from the reference sequence for TEM-1. Clinical use of this convenient, single-closed-tube assay would make it possible to rapidly distinguish ESBL from non-ESBL variants and thereby to begin early treatment with suitable antibiotics.

KRAS, BRAF, and TP53 Deep Sequencing for Colorectal Carcinoma Patient Diagnostics

2013-03-26

In colorectal carcinoma, KRAS (alias Ki-ras) and BRAF mutations have emerged as predictors of resistance to anti–epidermal growth factor receptor antibody treatment and worse patient outcome, respectively. In this study, we aimed to establish a high-throughput deep sequencing workflow according to 454 pyrosequencing technology to cope with the increasing demand for sequence information at medical institutions. A cohort of 81 patients with known KRAS mutation status detected by Sanger sequencing was chosen for deep sequencing. The workflow allowed us to analyze seven amplicons (one BRAF, two KRAS, and four TP53 exons) of nine patients in parallel in one deep sequencing run. Target amplification and variant calling showed reproducible results with input DNA derived from FFPE tissue that ranged from 0.4 to 50 ng with the use of different targets and multiplex identifiers. Equimolar pooling of each amplicon in a deep sequencing run was necessary to counterbalance differences in patient tissue quality. Five BRAF and 49 TP53 mutations with functional consequences were detected. The lowest mutation frequency detected in a patient tumor population was 5% in TP53 exon 5. This low-frequency mutation was successfully verified in a second PCR and deep sequencing run. In summary, our workflow allows us to process 315 targets a week and provides the quality, flexibility, and speed needed to be integrated as standard procedure for mutational analysis in diagnostics.

Novel Method for PIK3CA Mutation Analysis: Locked Nucleic Acid–PCR Sequencing

2013-03-28

Somatic mutations in PIK3CA are commonly seen in invasive breast cancer and several other carcinomas, occurring in three hotspots: codons 542 and 545 of exon 9 and in codon 1047 of exon 20. We designed a locked nucleic acid (LNA)-PCR sequencing assay to detect low levels of mutant PIK3CA DNA with attention to avoiding amplification of a pseudogene on chromosome 22 that has >95% homology to exon 9 of PIK3CA. We tested 60 FFPE breast DNA samples with known PIK3CA mutation status (48 cases had one or more PIK3CA mutations, and 12 were wild type) as identified by PCR-mass spectrometry. PIK3CA exons 9 and 20 were amplified in the presence or absence of LNA-oligonucleotides designed to bind to the wild-type sequences for codons 542, 545, and 1047, and partially suppress their amplification. LNA-PCR sequencing confirmed all 51 PIK3CA mutations; however, the mutation detection rate by standard Sanger sequencing was only 69% (35 of 51). Of the 12 PIK3CA wild-type cases, LNA-PCR sequencing detected three additional H1047R mutations in “normal” breast tissue and one E545K in usual ductal hyperplasia. Histopathological review of these three normal breast specimens showed columnar cell change in two (both with known H1047R mutations) and apocrine metaplasia in one. The novel LNA-PCR shows higher sensitivity than standard Sanger sequencing and did not amplify the known pseudogene.

Feasibility of a Novel Approach for Rapid Detection of Simulated Bloodstream Infections via Enzymatic Template Generation and Amplification (ETGA)–Mediated Measurement of Microbial DNA Polymerase Activity

Daniel R. Zweitzig, Bruce I. Sodowich, Nichol M. Riccardello, S. Mark O'Hara — 2013-03-13

Bloodstream infections (BSIs) caused by bacteria and fungi are associated with significant morbidity and mortality. Currently, blood culture is the gold standard for confirming a suspected BSI, but has the drawback of lengthy time-to-detection (TTD) required for indicating the presence of microbes. Detection of conserved microbial nucleic acid sequences within blood culture samples via PCR has been demonstrated to offer potential for reducing the TTD of BSI; however, these approaches have various other limitations. We report a novel approach toward rapid detection of microbes from simulated BSI via differential hematopoietic cell lysis followed by enzymatic template generation and amplification (ETGA)–mediated measurement of microbial DNA polymerase extension activity. The differential cell lysis procedure effectively reduced the level of detectable DNA polymerase extension activity associated with human-derived hematopoietic cells present in blood culture samples taken from healthy donors. After treatment with the differential cell lysis procedure, the ETGA assay detected a panel of clinically prevalent bacteria and Candida albicans from spiked blood culture samples. The ETGA blood culture method also reduced by threefold the TTD required for simulated BSI, compared with a continuous-monitoring blood culture instrument. In summary, these findings demonstrate the feasibility of an innovative approach toward a rapid, sensitive, and universal screen for microbes within blood culture samples. Potential for clinical application and automation are also addressed.

Molecular and Functional Analysis of the Large 5′ Promoter Region of CFTR Gene Revealed Pathogenic Mutations in CF and CFTR-Related Disorders

2013-03-07

Patients with cystic fibrosis (CF) manifest a multisystemic disease due to mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR); despite extensive testing of coding regions, a proportion of CF alleles remains unidentified. We studied 118 patients with CF and CFTR-related disorders, most with one or both unknown mutations after the scanning of CFTR coding regions, and a non-CF control group (n = 75) by sequencing the 6000-bp region at the 5′ of the CFTR gene. We identified 23 mutations, of which 9 were novel. We expressed such mutations in vitro using four cell systems to explore their functional effect, relating the data to the clinical expression of each patient. Some mutations reduced expression of the gene reporter firefly luciferase in various cell lines and may act as disease-causing mutations. Other mutations caused an increase in luciferase expression in some cell lines. One mutation had a different effect in different cells. For other mutations, the expression assay excluded a functional role. Gene variants in the large 5′ region may cause altered regulation of CFTR gene expression, acting as disease-causing mutations or modifiers of its clinical phenotype. Studies of in vitro expression in different cell systems may help reveal the effect of such mutations.

ALK Status Testing in Non–Small Cell Lung Carcinoma: Correlation Between Ultrasensitive IHC and FISH

2013-03-13

ALK gene rearrangements in advanced non–small cell lung carcinomas (NSCLC) are an indication for targeted therapy with crizotinib. Fluorescence in situ hybridization (FISH) using a recently approved companion in vitro diagnostic class FISH system commonly assesses ALK status. More accessible IHC is challenged by low expression of ALK-fusion transcripts in NSCLC. We compared ultrasensitive automated IHC with FISH for detecting ALK status on 318 FFPE and 40 matched ThinPrep specimens from 296 patients with advanced NSCLC. IHC was concordant with FFPE-FISH on 229 of 231 dual-informative samples (31 positive and 198 negative) and with ThinPrep-FISH on 34 of 34 samples (5 positive and 29 negative). Two cases with negative IHC and borderline-positive FFPE-FISH (15% and 18%, respectively) were reclassified as concordant based on negative matched ThinPrep-FISH and clinical data consistent with ALK-negative status. Overall, after including ThinPrep-FISH and amending the false-positive FFPE-FISH results, IHC demonstrated 100% sensitivity and specificity (95% CI, 0.86 to 1.00 and 0.97 to 1.00, respectively) for ALK detection on 249 dual-informative NSCLC samples. IHC was informative on significantly more samples than FFPE-FISH, revealing additional ALK-positive cases. The high concordance with FISH warrants IHC’s routine use as the initial component of an algorithmic approach to clinical ALK testing in NSCLC, followed by reflex FISH confirmation of IHC-positive cases.

Molecular Assays for Quantitative and Qualitative Detection of Influenza Virus and Oseltamivir Resistance Mutations

2013-04-18

Sensitive and reproducible molecular assays are essential for influenza virus diagnostics. This manuscript describes the design, validation, and evaluation of a set of real-time RT-PCR assays for quantification and subtyping of human influenza viruses from patient respiratory material. Four assays are included for detection of oseltamivir resistance mutations H275Y in prepandemic and pandemic influenza A/H1N1 and E119V and R292K in influenza A/H3N2 neuraminidase. The lower limits of detection of the quantification assay were determined to be 1.7 log10 virus particles per milliliter (vp/mL) for influenza A and 2.2 log10 vp/mL for influenza B virus. The lower limits of quantification were 2.1 and 2.3 log10 vp/mL, respectively. The RT-PCR efficiencies and lower limits of detection of the quantification assays were only marginally affected when tested on the most dissimilar target sequences found in the GenBank database. Finally, the resistance RT-PCR assays detected at least 5% mutant viruses present in mixtures containing both wild-type and mutant viruses with approximated limits of detection of 2.4 log10 vp/mL. Overall, this set of RT-PCR assays is a powerful tool for enhanced influenza virus surveillance.

Low Incidence of Minor BRAF V600 Mutation-Positive Subclones in Primary and Metastatic Melanoma Determined by Sensitive and Quantitative Real-Time PCR

Thomas Kristensen, Ole Clemmensen, Lise Hoejberg — 2013-03-13

BRAF V600 mutation is an important biological marker for therapeutic guidance in melanoma, where mutation-positive cases are candidates for therapy targeting mutant B-Raf. Recent studies showing intratumor variation in BRAF mutation status have caused concern that sensitive mutation analysis can lead to mutation-positive results in patients with melanomas with small subsets of mutation-positive cells who may not benefit from therapy targeting mutant B-Raf. Mutation analysis with high analytical sensitivity is generally preferred, to reduce the risk of false-negative results. In this study, sensitive and quantitative BRAF V600E and V600K mutation-specific real-time quantitative PCR was used to study the occurrence of small subsets of mutation-positive cells in primary melanomas and melanoma metastases. The BRAF V600E mutation was detected in 39 of 82 melanoma patients. We observed a highly dichotomous pattern, with most samples either testing mutation positive in a high fraction of alleles (median, 51%) or negative with a high sensitivity (median, 0.06%). This finding demonstrates that the occurrence of small subsets of mutation-positive cells was rare in our study population and indicates that sensitive mutation analysis can generally be expected to produce clinically relevant results in melanoma patients.

A DNA Microarray for the Detection of Point Mutations and Copy Number Variation Causing Familial Hypercholesterolemia in Europe

2013-03-27

To facilitate genetic cascade screening for familial hypercholesterolemia (FH) in Europe, two versions (7 and 9) of a DNA microarray were developed to detect the most frequent point mutations in the low-density lipoprotein receptor (LDLR), apolipoprotein B (APOB), and proprotein convertase subtilisin/kexin 9 (PCSK9) genes. The design of these microarrays is based on LIPOchip, version 4, which detects 191 LDLR and APOB mutations identified in Spanish patients with FH. A major improvement of LIPOchip, versions 7 and 9, is the ability to detect copy number variation (deletions or duplications of entire exons) in LDLR, thus abolishing the need to perform multiplex ligase-dependent probe amplification in patients with FH. The aim of this study was to validate a tool capable of detecting point mutations and copy number variations simultaneously and to evaluate its use and the newly developed software for analysis in clinical practice by reanalysis of several patients with known mutations causing FH. With the help of these validations, several aspects were analyzed, improved, and implemented in a newer version, which was evaluated through an internal validation.

Performance of the Linear Array HPV Genotyping Test on Paired Cytological and Formalin-Fixed, Paraffin-Embedded Cervical Samples

2013-03-25

Detection and genotyping of human papillomavirus (HPV) from formalin-fixed, paraffin-embedded (FFPE) samples may be difficult when using assays based on amplification of large fragments. The objective of the present study was to investigate the performance of the Linear Array HPV Genotyping Test (Linear Array) on FFPE cervical cone biopsy specimens using paired cytologic samples obtained immediately before the conization as a criterion standard. Thirty-nine samples of grade 2 or higher cervical intraepithelial neoplasia were selected; all of the corresponding cytological samples were positive by the Linear Array and had a report of atypical squamous cells of undetermined significance or worse. A valid Linear Array test result was obtained for 38 FFPE specimens (97.4%, 95% CI 88.0 to 99.9). Specifically, 34 were HPV-positive (89.5%, 95% CI 76.5 to 96.9) and 4 were HPV-negative (10.5%, 95% CI 3.4 to 23.5). The overall agreement of the results obtained for the cytologic and histologic paired samples was good (Cohen’s κ = 0.85, SE = 0.082, P = 0.000). Further analysis of samples with negative or invalid Linear Array test results, both modifying the nucleic acids extraction protocol and using the INNO-LiPA assay, suggested that failure of the Linear Array test in HPV detection from tissues was probably due to DNA fragmentation. Parallel analysis of paired FFPE and cytologic samples is extremely useful for evaluation of the efficiency of PCR-based assays in HPV detection and genotyping from tissue samples. In the present study, false-negative results were obtained in a limited percentage of cases, our data depicting the successful performance of the Linear Array test on FFPE samples.

Evaluating the Effect of Unclassified Variants Identified in MMR Genes Using Phenotypic Features, Bioinformatics Prediction, and RNA Assays

2013-03-25

Lynch syndrome is caused by mutations in one of the mismatch-repair system (MMR) genes. A major difficulty in diagnosis and management of Lynch syndrome is the existence of unclassified genetic variants (UVs) with unknown clinical significance, especially mutations with new descriptions and missense-type nucleotide substitutions. We evaluated the pathogenicity of 20 such mutations (6 in MLH1, 4 in MSH2, and 7 in MSH6) found in Spanish patients suspected of Lynch syndrome. The UVs were tested for evidence of MMR defect in tumor samples and were evaluated for co-occurrence with a pathogenic mutation, the cosegregation of the variant with the disease; where sufficient data were available, in silico resources at the protein level and mRNA analysis were used to assess the putative effect on the splicing mechanism. To evaluate the frequency of these UVs in the general population, a case–control study was also performed. Five variants were identified with similar frequencies in both cases and controls, suggesting a nonpathogenic effect in patients. In contrast, abnormal splicing mutations were detected in a high proportion of patients [3/20 (15%)]. In this study, we classified 15 of the 20 UVs: six variants with strong evidence of pathogenicity and nine variants that should be considered neutral variants. Clinical significance of the other five remains unknown.

Quality Control Methods for Optimal BCR-ABL1 Clinical Testing in Human Whole Blood Samples

2013-03-28

Reliable breakpoint cluster region (BCR)–Abelson (ABL) 1 measurement is essential for optimal management of chronic myelogenous leukemia. There is a need to optimize quality control, sensitivity, and reliability of methods used to measure a major molecular response and/or treatment failure. The effects of room temperature storage time, different primers, and RNA input in the reverse transcription (RT) reaction on BCR-ABL1 and β-glucuronidase (GUSB) cDNA yield were assessed in whole blood samples mixed with K562 cells. BCR-ABL1 was measured relative to GUSB to control for sample loading, and each gene was measured relative to known numbers of respective internal standard molecules to control for variation in quality and quantity of reagents, thermal cycler conditions, and presence of PCR inhibitors. Clinical sample and reference material measurements with this test were concordant with results reported by other laboratories. BCR-ABL1 per 103 GUSB values were significantly reduced (P = 0.004) after 48-hour storage. Gene-specific primers yielded more BCR-ABL1 cDNA than random hexamers at each RNA input. In addition, increasing RNA inhibited the RT reaction with random hexamers but not with gene-specific primers. Consequently, the yield of BCR-ABL1 was higher with gene-specific RT primers at all RNA inputs tested, increasing to as much as 158-fold. We conclude that optimal measurement of BCR-ABL1 per 103 GUSB in whole blood is obtained when gene-specific primers are used in RT and samples are analyzed within 24 hours after blood collection.

Detection of HIV-1 Minority Variants Containing the K103N Drug-Resistance Mutation Using a Simple Method to Amplify RNA Targets (SMART)

Kenneth Morabito, Rami Kantor, Warren Tai, Leeann Schreier, Anubhav Tripathi — 2013-04-01

The simple method for amplifying RNA targets (SMART) was used to detect K103N, a common HIV-1 reverse transcriptase drug-resistance mutation. Novel amplifiable SMART probes served as reporter molecules for RNA sequences that are captured and separated on a microfluidic platform under zero-flow conditions. Assays were performed both off chip and in a microchip reservoir using a modified version of real-time nucleic acid sequence-based amplification, without the noncyclic phase, and 65°C preheat. A total of 6000 copies/mL of the synthetic sequences were detected within 180 minutes of amplification. Although the sensitivity of research platforms is higher, SMART has the potential to offer comparable sensitivity and speed to commercially available viral load and HIV detection kits. Furthermore, SMART uses an inexpensive, practical, and more accurate isothermal exponential amplification technique. The use of molecular beacons resulted in relatively fast real-time detection (<180 minutes); however, they were also shown to hinder the amplification process when compared with end point detection. Finally, SMART probes were used for modeling of K103N concentrations within an unknown sample. Only 1% of the SMART probes was detected within the wild-type population (6 × 108 copies/mL). These results establish the groundwork for point-of-care drug resistance and viral load monitoring in clinical samples, which can revolutionize HIV patient care globally.

Editorial Board

2013-05-01

The Journal of Molecular Diagnostics

Visual Automated Fluorescence Electrophoresis Provides Simultaneous Quality, Quantity, and Molecular Weight Spectra for Genomic DNA from Archived Neonatal Blood Spots

Rapid Detection of TEM-Type Extended-Spectrum β-Lactamase (ESBL) Mutations Using Lights-On/Lights-Off Probes with Single-Stranded DNA Amplification

KRAS, BRAF, and TP53 Deep Sequencing for Colorectal Carcinoma Patient Diagnostics

Novel Method for PIK3CA Mutation Analysis: Locked Nucleic Acid–PCR Sequencing

Feasibility of a Novel Approach for Rapid Detection of Simulated Bloodstream Infections via Enzymatic Template Generation and Amplification (ETGA)–Mediated Measurement of Microbial DNA Polymerase Activity

Molecular and Functional Analysis of the Large 5′ Promoter Region of CFTR Gene Revealed Pathogenic Mutations in CF and CFTR-Related Disorders

ALK Status Testing in Non–Small Cell Lung Carcinoma: Correlation Between Ultrasensitive IHC and FISH

Molecular Assays for Quantitative and Qualitative Detection of Influenza Virus and Oseltamivir Resistance Mutations

Low Incidence of Minor BRAF V600 Mutation-Positive Subclones in Primary and Metastatic Melanoma Determined by Sensitive and Quantitative Real-Time PCR

A DNA Microarray for the Detection of Point Mutations and Copy Number Variation Causing Familial Hypercholesterolemia in Europe

Performance of the Linear Array HPV Genotyping Test on Paired Cytological and Formalin-Fixed, Paraffin-Embedded Cervical Samples

Evaluating the Effect of Unclassified Variants Identified in MMR Genes Using Phenotypic Features, Bioinformatics Prediction, and RNA Assays

Quality Control Methods for Optimal BCR-ABL1 Clinical Testing in Human Whole Blood Samples

Detection of HIV-1 Minority Variants Containing the K103N Drug-Resistance Mutation Using a Simple Method to Amplify RNA Targets (SMART)

Editorial Board

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