High resolution melting analysis: a rapid and accurate method to detect CALR mutations

Screening of somatic mutations in the JAK2 and CALR genes by high-resolution melting curve analysis

Somatic mutations associated with oncological diseases, including Ph-myeloproliferative neoplasms (Ph-MPN), are very diverse, occur with different frequencies and different allelic burden levels. Therefore, at the initial stage of performing molecular-genetic diagnostic procedures, it is desirable to be able to conduct screening tests in the laboratory. This is especially important when analyzing rare and diverse mutations. Analysis of high resolution melting curves (HRM analysis), which has high sensitivity and is suitable for screening all types of mutations, in a number of studies is proposed for the analysis of Ph-MPN associated mutations in the JAK2 and CALR genes. For analysis of somatic mutations in the majority of literature sources that we reviewed, the authors use the LightCycler (Roche) thermocycler and much rarely the CFX96 (Bio-Rad), which is often presented in Russian scientific and practical and medical organizations. The aim of the study was to screen the somatic JAK2 and CALR mutations by HRM analysis using the CFX96 thermocycler and the Precision Melt Analysis software (Bio-Rad, USA) for patients with Ph-MPN. In the present research, HRM analysis was conducted on the DNA samples from patients with mutations in the JAK2 or in the CALR gene. The Precision Melt Analysis software identified all variants of the analyzed mutations, both a single nucleotide substitution in the JAK2 gene (with allelic burden level in the range of 5-40%), and various indel mutations in the CALR gene (with allelic burden level in the range of 40-50%) Therefore, the HRM analysis that was conducted on the CFX96 allows screening of highly specific mutation for the diagnosis of Ph-MPN in the exon 14 of the JAK2 gene and in the exon 9 of the CALR gene. The inclusion of this screening research in the laboratory testing algorithm improves the efficiency and accessibility of molecular genetic technologies in the diagnosis of Ph-MPN.

The Contemporary Approach to CALR-Positive Myeloproliferative Neoplasms

CALR mutations are a revolutionary discovery and represent an important hallmark of myeloproliferative neoplasms (MPN), especially essential thrombocythemia and primary myelofibrosis. To date, several CALR mutations were identified, with only frameshift mutations linked to the diseased phenotype. It is of diagnostic and prognostic importance to properly define the type of CALR mutation and subclassify it according to its structural similarities to the classical mutations, a 52-bp deletion (type 1 mutation) and a 5-bp insertion (type 2 mutation), using a statistical approximation algorithm (AGADIR). Today, the knowledge on the pathogenesis of CALR-positive MPN is expanding and several cellular mechanisms have been recognized that finally cause a clonal hematopoietic expansion. In this review, we discuss the current basis of the cellular effects of CALR mutants and the understanding of its implementation in the current diagnostic laboratorial and medical practice. Different methods of CALR detection are explained and a diagnostic algorithm is shown that aids in the approach to CALR-positive MPN. Finally, contemporary methods joining artificial intelligence in accordance with molecular-genetic biomarkers in the approach to MPN are presented.

Detection of CALR Mutations Using High Resolution Melting Curve Analysis (HRM-A); Application on a Large Cohort of Greek ET and MF Patients

Background and Objectives

Somatic mutations in the calreticulin gene (CALR) are detected in approximately 70% of patients with essential thrombocythemia (ET) and primary or secondary myelofibrosis (MF), lacking the JAK2 and MPL mutations. To determine the prevalence of CALR frameshift mutations in a population of MPN patients of Greek origin, we developed a rapid low-budget PCR-based assay and screened samples from 5 tertiary Haematology units. This is a first of its kind report of the Greek patient population that also disclosed novel CALR mutants.

Methods

MPN patient samples were collected from different clinical units and screened for JAK2 and MPL mutations after informed consent was obtained. Negative samples were analyzed for the presence of CALR mutations. To this end, we developed a modified post Real Time PCR High-Resolution Melting Curve analysis (HRM-A) protocol. Samples were subsequently confirmed by Sanger sequencing.

Results

Using this protocol we screened 173 MPN, JAK2 and MPL mutation negative, patients of Greek origin, of whom 117 (67.63%) displayed a CALR exon nine mutation. More specifically, mutations were detected in 90 out of 130 (69.23%) essential thrombocythaemia cases (ET), in 18 out of 33 (54.55%) primary myelofibrosis patients (pMF) and in 9 out of 10 (90%) cases of myelofibrosis secondary to ET (post-ET sMF). False positive results were not detected. The limit of detection (LoD) of our protocol was 2%. Furthermore, our study revealed six rare novel mutations which are to be added in the COSMIC database.

Conclusions

Overall, our method could rapidly and cost-effectively detect the mutation status in a representative cohort of Greek patients; the mutation make-up in our group was not different from what has been published for other national groups.

A triplex probe-based TaqMan qPCR assay for Calreticulin type I and II mutation detection

BACKGROUND

Calreticulin (CALR) exon 9 frameshift mutations have recently been identified in 30-40% of patients with essential thrombocythemia (ET) and primary myelofibrosis (PMF) without JAK2 or MPL mutations. We aimed to develop a qPCR assay to screen type I and II mutations of CALR.

METHODS

Three different fluorescent-labeled hydrolysis probes and one pair of primers in a closed-tube system were developed to detect CALR type I and II mutations and distinguish them from wild-type. The sensitivity and specificity were validated using TA-cloning plasmids containing CALR wild-type and type I and II mutants, respectively. Fifty-nine ET and PMF specimens were screened by TaqMan qPCR and sequenced by Sanger sequencing. For intra-assay validation, 20 replicates of the assay were performed with each sample. For inter-assay validation, four replications of each sample were carried out and repeated continuously for 5 days.

RESULTS

We found that triplex probe-based TaqMan qPCR was reliable in detecting CALR type I and II mutants within DNA that was diluted to 1% of total DNA with the wild-type DNA as background. In 59 patient specimens, six of the observed mutations of CALR were type I and five were type II. Genotyping results obtained from TaqMan qPCR were 100% concordant with Sanger sequencing. The intra- and inter-assay CVs of TaqMan qPCR were less than 3%, respectively.

CONCLUSIONS

Triplex probe-based TaqMan qPCR is an accurate and sensitive method for screening ET or PMF patients with type I and II mutations in CALR.

Prognostic implications of low transferrin saturation in patients with primary myelofibrosis

OBJECTIVES

Transferrin saturation (TSAT) 20% or less is considered to represent functional iron deficiency in the context of malignant disease, phenomenon mediated through inflammatory changes of iron homeostasis. We aimed to investigate clinical and prognostic significance of low TSAT in patients with primary (PMF) and secondary myelofibrosis (SMF), malignant diseases characterized by strong inflammatory milieu.

METHODS

We retrospectively analyzed 87 patients with myelofibrosis and compared TSAT with disease specific parameters.

RESULTS

One-third of patients had TSAT ≤20%. Lower TSAT was significantly associated with Janus-kinase-2 (JAK2) mutation (P = 0.007), transfusion independency (P = 0.003), higher platelets (P = 0.004), lower mean-corpuscular-volume (P < 0.001), lower ferritin (P < 0.001), higher absolute-neutrophil-count (P = 0.027), lower absolute-lymphocyte-count (P = 0.041) and lower albumin (P = 0.018). PMF patients presenting with low TSAT (≤20%) experienced significantly shorter overall-survival (OS) (HR = 2.43; P = 0.017), whereas TSAT did not affect OS of SMF patients (HR = 1.48; P = 0.623). Low TSAT remained significantly associated with inferior OS in PMF in a series of multivariate Cox regression models comparing its properties to anemia, transfusion dependency, ferritin and Dynamic-International-Prognostic-System (DIPSS).

CONCLUSIONS

Low TSAT has detrimental effect on survival of PMF patients. This effect is independent of anemia and of ferritin levels that seem to be better at representing iron overload in PMF patients.

A Comparison of Techniques to Evaluate the Effectiveness of Genome Editing

Genome editing using engineered nucleases (meganucleases, zinc finger nucleases, transcription activator-like effector nucleases) has created many recent breakthroughs. Prescreening for efficiency and specificity is a critical step prior to using any newly designed genome editing tool for experimental purposes. The current standard screening methods of evaluation are based on DNA sequencing or use mismatch-sensitive endonucleases. They can be time-consuming and costly or lack reproducibility. Here, we review and critically compare standard techniques with those more recently developed in terms of reliability, time, cost, and ease of use.

Assessing serum albumin concentration, lymphocyte count and prognostic nutritional index might improve prognostication in patients with myelofibrosis

BACKGROUND

Primary and secondary myelofibrosis (PMF and SMF) are malignant diseases of hematopoietic stem cell characterized by the neoplastic myeloproliferation and a strong inflammatory milieu. The prognostic nutritional index (PNI) integrates information on albumin and absolute lymphocyte count (ALC) and reflects the inflammatory, nutritional and immune status of a patient. The clinical and prognostic significance of albumin, ALC and PNI in patients with myelofibrosis has not been previously investigated.

METHODS

We retrospectively analyzed a cohort of 83 myelofibrosis patients treated in our institution from 2006 to 2017. Albumin, ALC and PNI were assessed in addition to other disease specific markers.

RESULTS

The PMF and SMF patients had significantly lower ALC and PNI but similar albumin compared to controls. Lower albumin was significantly associated with older age and parameters reflecting more aggressive disease biology (e.g. anemia, lower platelet levels, higher lactate dehydrogenase (LDH), circulatory blasts, transfusion dependency, blast phase disease), inflammation (higher C reactive protein (CRP), constitutional symptoms) and higher degree of bone marrow fibrosis. Lower ALC was significantly associated with lower white blood cells (WBC) and lower circulatory blasts. Low PNI was associated with lower albumin, lower ALC, anemia, lower WBCs, lower serum iron and lower transferrin saturation. There was no difference in albumin, ALC and PNI regarding the driver mutations. In multivariate analysis adjusted for age and gender, low albumin (hazard ratio [HR] = 4.61, P = 0.001), low ALC (HR = 3.54, P = 0.004) and Dynamic International Prognostic Scoring System (DIPSS) (HR = 2.45, P = 0.001) were able to predict inferior survival independently of each other. Accordingly, low PNI (HR = 4.32, P < 0.001) predicted poor survival independently of DIPSS (HR = 3.31, P < 0.001).

CONCLUSION

Assessing albumin, ALC and PNI might improve prognostication in patients with myelofibrosis and could assist in recognition of patients under increased risk of death.

CALR mutation characterization in myeloproliferative neoplasms

Identification of somatic frameshift mutations in exon 9 of the calreticulin gene (CALR) in myeloproliferative neoplasms (MPNs) in December of 2013 has been a remarkable finding. It has provided a new molecular diagnostic marker, particularly in essential thrombocythemia (ET) and primary myelofibrosis (PMF), where is the second most common altered gene after JAK2V617F. There are two main types of CALR mutants, type 1 and type 2, and there is evidence about their distinct clinical/prognostic implications, for instances, it is believed that favorable outcome might be restricted to type-1 in PMF. By using reasoned approaches, very recent publications have supported classifying the alternative mutants in type-1-like or type-2-like. If further studies confirm these results, new considerations may be taken into account in the molecular diagnosis of MPNs. This implies that precise mutation characterization must be performed and caution should be taken in screening technique selection. In this Editorial we summarize the current information regarding all this issues.

Screening PCR Versus Sanger Sequencing: Detection of CALR Mutations in Patients With Thrombocytosis

Background

Mutations in calreticulin (CALR) have been reported to be key markers in the molecular diagnosis of myeloid proliferative neoplasms. In most previous reports, CALR mutations were analyzed by using Sanger sequencing. Here, we report a new, rapid, and convenient system for screening CALR mutations without sequencing.

Methods

Eighty-three bone marrow samples were obtained from 81 patients with thrombocytosis. PCR primers were designed to detect wild-type CALR (product: 357 bp) and CALR with type 1 (product: 302 bp) and type 2 mutations (product: 272 bp) in one reaction. The results were confirmed by Sanger sequencing and compared with results from fragment analysis.

Results

The minimum detection limit of the screening PCR was 10 ng for type 1, 1 ng for type 2, and 0.1 ng for cases with both mutations. CALR type 1 and type 2 mutants were detected with screening PCR with a maximal analytical sensitivity of 3.2% and <0.8%, respectively. The screening PCR detected 94.1% (16/17) of mutation cases and showed concordant results with sequencing in the cases of type 1 and type 2 mutations. Sanger sequencing identified one novel mutation (c.1123_1132delinsTGC). Compared with sequencing, the screening PCR showed 94.1% sensitivity, 100.0% specificity, 100.0% positive predictive value, and 98.5% negative predictive value. Compared with fragment analysis, the screening PCR presented 88.9% sensitivity and 100.0% specificity.

Conclusions

This screening PCR is a rapid, sensitive, and cost-effective method for the detection of major CALR mutations.

A novel molecular assay using hybridisation probes and melt curve analysis for CALR exon 9 mutation detection in myeloproliferative neoplasms

AIMS

Somatic insertions/deletions in exon 9 of the calreticulin gene have been identified in patients with essential thrombocythemia and primary myelofibrosis. Over 55 mutations have been discovered, 80% of which consist of either type 1 52-bp deletion or type 2 5-bp insertion. Other mutations (types 3-5) in conjunction with types 1 and 2 account for >87% of identified mutations. The aim of this study was development of a rapid PCR-based assay using LightCycler Hybridisation Probes for the detection of type 1-5 CALR mutations.

METHOD

A real-time PCR assay using a novel HybProbe set was developed for use on the LightCycler 480 Instrument II. The acceptor probe was labelled with LC640 and Faststart DNA Master HybProbe kit was used for PCR reactions.

RESULTS

Assay limit of detection was determined to be seven target copies with a probability of 95%. The specificity of the assay was determined by using synthetic constructs of CALR wild-type and CALR mutation types 1-5 with no non-specific detection observed. Samples from 21 patients with essential thrombocythemia (ET) and 12 patients with primary myelofibrosis (PMF), together with 29 control samples from patients diagnosed with various conditions, were screened using the assay. Of these, 24 were found to have mutations in CALR exon 9, with the assay detecting 8 type 1 mutations, 12 type 2 mutations, 2 type 24 mutations, 1 type 20 mutation and 1 31-bp deletion.

CONCLUSIONS

The novel assay described has potential for application as a rapid, sensitive, high-throughput screening method in the clinical diagnostics setting.

Detection of CALR Mutation in Clonal and Nonclonal Hematologic Diseases Using Fragment Analysis and Next-Generation Sequencing

OBJECTIVES

To describe three methods used to screen for frameshift mutations in exon 9 of the CALR gene.

METHODS

Genomic DNA from 47 patients was extracted from peripheral blood and bone marrow using the EZ1 DNA Blood Kit (Qiagen, Valencia, CA) and quantified by the Quant-iT PicoGreen dsDNA Assay Kit (Invitrogen, San Diego, CA). After clinical history, cytogenetics, and molecular tests, patients were diagnosed with either clonal or nonclonal hematologic diseases. CALR screening was primarily performed using fragment analysis polymerase chain reaction, then next-generation sequencing and Sanger sequencing.

RESULTS

Among the 18 patients diagnosed with clonal diseases, one had acute myeloid leukemia (positive for trisomy 8), and 17 had myeloproliferative neoplasms (MPNs), including chronic myeloid leukemia (CML), essential thrombocythemia (ET), primary myelofibrosis (PMF), and polycythemia vera (PV). Patients with CML were positive for the BCR-ABL1 fusion. Ten patients were positive for JAK2 (PMF, n = 1; ET, n = 2; PV, n = 7), and three were CALR positive (ET, n = 1; PMF, n = 2). Patients diagnosed with a nonclonal disease were negative for JAK2, BCR-ABL, and CALR mutations.

CONCLUSIONS

Screening for CALR mutations is essential in BCR-ABL-negative MPNs since it not only provides valuable diagnostic and prognostic information but also identifies potential treatment targets. Since this study describes the importance of screening for known and novel biomarkers, we described in detail three methods that could be easily integrated into a clinical laboratory.

Simultaneous screening for JAK2 and calreticulin gene mutations in myeloproliferative neoplasms with high resolution melting

INTRODUCTION

Recently, novel calreticulin (CALR) mutations were discovered in Janus kinase 2 (JAK2) non-mutated myelofibrosis (PMF) and essential thrombocythemia (ET) cases, with a frequency of 60-80%. We examined clinical correlations and CALR mutation frequency in our myeloproliferative neoplasms (MPN) cases, and introduce an effective test method for use in clinical practice.

METHODS

We examined 177 samples previously investigated for the JAK2 mutation for differential diagnosis of MPN. JAK2 and CALR mutations were analyzed using melting curve analysis and microchip electrophoresis, respectively. Next, we constructed a test for simultaneous screening of the JAK2 and CALR mutations utilizing high resolution melting (HRM).

RESULTS

Among 99 MPN cases, 60 possessed the JAK2 mutation alone. Of the 39 MPN cases without the JAK2 mutation, 14 were positive for the CALR mutation, all of which were ET. Using our novel screening test for the JAK2 and CALR mutations by HRM, the concordance rate of conventional analysis with HRM was 96% for the JAK2 mutation and 95% for the CALR mutation.

CONCLUSION

Our novel simultaneous screening test for the JAK2 and CALR gene mutations with HRM is useful for diagnosis of MPN.

Genetic characterization of poxviruses in Camelus dromedarius in Ethiopia, 2011-2014

Camelpox and camel contagious ecthyma are infectious viral diseases of camelids caused by camelpox virus (CMLV) and camel contagious ecthyma virus (CCEV), respectively. Even though, in Ethiopia, pox disease has been creating significant economic losses in camel production, little is known on the responsible pathogens and their genetic diversity. Thus, the present study aimed at isolation, identification and genetic characterization of the causative viruses. Accordingly, clinical case observations, infectious virus isolation, and molecular and phylogenetic analysis of poxviruses infecting camels in three regions and six districts in the country, Afar (Chifra), Oromia (Arero, Miyu and Yabello) and Somali (Gursum and Jijiga) between 2011 and 2014 were undertaken. The full hemagglutinin (HA) and partial A-type inclusion protein (ATIP) genes of CMLV and full major envelope protein (B2L) gene of CCEV of Ethiopian isolates were sequenced, analyzed and compared among each other and to foreign isolates. The viral isolation confirmed the presence of infectious poxviruses. The preliminary screening by PCR showed 27 CMLVs and 20 CCEVs. The sequence analyses showed that the HA and ATIP gene sequences are highly conserved within the local isolates of CMLVs, and formed a single cluster together with isolates from Somalia and Syria. Unlike CMLVs, the B2L gene analysis of Ethiopian CCEV showed few genetic variations. The phylogenetic analysis revealed three clusters of CCEV in Ethiopia with the isolates clustering according to their geographical origins. To our knowledge, this is the first report indicating the existence of CCEV in Ethiopia where camel contagious ecthyma was misdiagnosed as camelpox. Additionally, this study has also disclosed the existence of co-infections with CMLV and CCEV. A comprehensive characterization of poxviruses affecting camels in Ethiopia and the full genome sequencing of representative isolates are recommended to better understand the dynamics of pox diseases of camels and to assist in the implementation of more efficient control measures.

Clinical validation of a multipurpose assay for detection and genotyping of CALR mutations in myeloproliferative neoplasms

OBJECTIVES

To develop a polymerase chain reaction (PCR)-based approach to detect CALR mutations in myeloproliferative neoplasms (MPNs) in a clinical laboratory.

METHODS

DNA was extracted from bone marrow aspirate samples of 67 JAK2 wild-type MPNs (22 with matched peripheral blood), 54 cases of unclassifiable myelodysplastic syndrome/MPN, and 16 cases of atypical chronic myeloid leukemia. We used genomic DNA to detect somatic mutations in exon 9 of CALR and PCR with fluorescently labeled and M13-tagged primers and subjected the products to capillary electrophoresis (CE) followed by Sanger sequencing. Detailed assay performance characteristics were established.

RESULTS

We identified CALR mutations in 19 (28.4%) of 67 JAK2-negative MPNs, including 14 type I (52-base pair [bp] deletion), four type II (5-bp insertions), and one type III (18-bp deletion). All mutations were confirmed by Sanger sequencing. Sensitivity studies showed 2.5% and 5% mutation detection levels by CE and Sanger sequencing, respectively, with high reproducibility.

CONCLUSIONS

This assay allows for rapid, convenient screening for CALR mutations in MPNs, thereby reducing the number of cases that require assessment by Sanger sequencing, reducing labor and improving turnaround time.

Development and validation of CALR mutation testing for clinical diagnosis

OBJECTIVES

To validate a diagnostic assay for detecting CALR mutations in the clinical setting.

METHODS

Traditional polymerase chain reaction (PCR) was performed on DNA previously extracted from 60 specimens (30 bone marrow aspirates [BMAs] and 30 peripheral blood [PB] samples) from 55 patients. Nearly all reported CALR mutations are insertions or deletions in exon 9. Therefore, we performed amplicon sizing by capillary electrophoresis and fragment length analysis (FLA) to determine mutation status. Mutations were confirmed by Sanger sequencing.

RESULTS

Fourteen samples from 10 patients with JAK2 and MPL wild-type myeloproliferative neoplasms were positive for CALR mutation. Detected mutations included a 52-base pair (bp) deletion (n = 6), a 5-bp insertion (n = 2), a 31-bp deletion (n = 1), and a 61-bp deletion (n = 1). Sanger sequencing of 15 samples showed 100% concordance. Matched patient PB and BMA samples (n = 5) harbored identical mutations, and samples run multiple times (n = 8) showed 100% reproducibility.

CONCLUSIONS

We conclude that CALR mutations may be quickly and accurately detected by FLA of PCR amplicons by capillary electrophoresis. These methods are routine procedures for most molecular laboratories and should allow for straightforward incorporation of the CALR assay into the clinical diagnostic testing menu.

Calreticulin Mutations in Myeloproliferative Neoplasms: Comparison of Three Diagnostic Methods

Calreticulin (CALR) mutations have recently been reported in 70–84% of JAK2V617F-negative myeloproliferative neoplasms (MPN), and this detection has become necessary to improve the diagnosis of MPN. In a large single-centre cohort of 298 patients suffering from Essential Thrombocythemia (ET), the JAK2V617F, CALR and MPL mutations were noted in 179 (60%), 56 (18.5%) and 13 (4.5%) respectively. For the detection of the CALR mutations, three methods were compared in parallel: high-resolution melting-curve analysis (HRM), product-sizing analysis and Sanger sequencing. The sensitivity for the HRM, product-sizing analysis and Sanger sequencing was 96.4%, 98.2% and 89.3% respectively, whereas the specificity was 96.3%, 100% and 100%. In our cohort, the product-sizing analysis was the most sensitive method and was the easiest to interpret, while the HRM was sometimes difficult to interpret. In contrast, when large series of samples were tested, HRM provided results more quickly than did the other methods, which required more time. Finally, the sequencing method, which is the reference method, had the lowest sensitivity but can be used to describe the type of mutation precisely. Altogether, our results suggest that in routine laboratory practice, product-sizing analysis is globally similar to HRM for the detection of CALR mutations, and that both may be used as first-line screening tests. If the results are positive, Sanger sequencing can be used to confirm the mutation and to determine its type. Product-sizing analysis provides sensitive and specific results, moreover, with the quantitative measurement of CALR, which might be useful to monitor specific treatments.

Molecular diagnostics of myeloproliferative neoplasms

Since the discovery of the JAK2 V617F mutation in the majority of the myeloproliferative neoplasms (MPN) of polycythemia vera, essential thrombocythemia and primary myelofibrosis ten years ago, further MPN-specific mutational events, notably in JAK2 exon 12, MPL exon 10 and CALR exon 9 have been identified. These discoveries have been rapidly incorporated into evolving molecular diagnostic algorithms. Whilst many of these mutations appear to have prognostic implications, establishing MPN diagnosis is of immediate clinical importance with selection, implementation and the continual evaluation of the appropriate laboratory methodology to achieve this diagnosis similarly vital. The advantages and limitations of these approaches in identifying and quantitating the common MPN-associated mutations are considered herein with particular regard to their clinical utility. The evolution of molecular diagnostic applications and platforms has occurred in parallel with the discovery of MPN-associated mutations, and it therefore appears likely that emerging technologies such as next-generation sequencing and digital PCR will in the future play an increasing role in the molecular diagnosis of MPN.

Clinical relevance between CALR mutation and myeloproliferative neoplasms

In late 2013, somatic mutations in calreticulin (CALR), mainly those involving insertions and deletions in exon 9, attracted the great attention of hematologists and researchers. These JAK2- and MPL- mutual exclusive mutations enjoy a favorable specificity and prevalence (20-30%) in patients with essential thrombocythemia (ET) and primary myelofibrosis (PMF), suggesting promise for these mutations in disease management. Moreover, these genetic variations are now also considered as a group of independent risk factors for disease prognosis. In this mini-review, we will document the value of CALR mutations in disease diagnosis, prognosis, and therapeutic strategy selection, and we will discuss current advances in methods to detect these mutations.

Rapid and sensitive detection of CALR exon 9 mutations using high-resolution melting analysis

BACKGROUND

Somatic CALR exon 9 mutations have recently been identified in patients with JAK2/MPL-unmutated myeloproliferative neoplasm, and have become an important clonal marker for the diagnosis of essential thrombocythemia (ET) and primary myelofibrosis. In the present study, we sought to use high-resolution melting analysis (HRMA) as a screening method for the detection of CALR mutations.

METHODS

32 JAK2/MPL-unmutated ET patients were retrospectively enrolled and 8 healthy adults were used as wild-type control. CALR exon 9 mutation was independently screened by HRMA with the CFX Connect real-time system and Sanger sequencing. TA-cloning was used to detect CALR exon 9 mutations in patients suspected to have low mutant allele burden.

RESULTS

The maximal sensitivity of HRMA in identifying both CALR type 1 and type 2 mutants from patients' genomic DNA was 2.5%. Twenty-two samples were found to have distinct melting curves from wild-type. The presence of CALR mutations in 16 of these 22 samples was confirmed by Sanger sequencing, while the other 6 samples were wild-type by sequencing. After TA-cloning, CALR mutations were detected in 5 of 6 patients from 1 (6%) of 16 clones to 1 (2%) of 50 clones. Therefore, HRMA identified CALR mutations in 21 (65.6%) of 32 ET patients compared to 16 (50%) patients by Sanger sequencing, with a false positive rate of 3% and no false negative.

CONCLUSION

The HRMA developed in our system is a rapid and sensitive technique for the detection of CALR exon 9 mutations.

Calreticulin mutations in myeloproliferative neoplasms and new methodology for their detection and monitoring

The diagnosis of the BCR-ABL-negative myeloproliferative neoplasms (MPN), namely polycythemia vera, essential thombocythemia and primary myelofibrosis has relied significantly on the detection of known causative mutations in the JAK2 or MPL genes, which account for the majority of MPN patients. However, around 30 % of patients with MPN, primarily essential thombocythemia and primary myelofibrosis, lack mutations in these two genes making it difficult to reach a confident diagnosis in these cases. The recent discovery of frameshift mutations in CALR in approximately 70 % of MPN patients lacking the JAK2 and MPL mutations offers a reliable diagnostic marker for the latter group. A review of the current literature, plus unpublished data from our laboratory, shows that 55 different CALR insertion/deletion mutations have been identified so far in MPN patients. Among these 55 variants reported to date, a 52-base pair deletion and a 5-base pair insertion are by far the most prominent representing 50 and 35 %, respectively, of all cases with CALR mutations. In this paper, we describe a high-resolution melting (HRM) analysis and a Taqman® Real-Time PCR (RQ-PCR) assay and we propose a new clinical laboratory diagnostic algorithm for CALR mutation analysis. According to this algorithm, samples can go through front-line screening with HMR or fragment analysis, followed by the newly developed RQ-PCR to both discriminate and quantify the two most common mutations in CALR gene.