Simple, efficient, and cost-effective multiplex genotyping with matrix assisted laser desorption/ionization time-of-flight mass spectrometry of hemoglobin beta gene mutations

The role of molecular diagnostic testing for hemoglobinopathies and thalassemias

Hemoglobin disorders are among the most common genetic diseases worldwide. Molecular diagnosis is helpful in cases where the diagnosis is uncertain and for genetic counseling. Protein-based diagnostic techniques are frequently adequate for initial diagnosis. Molecular genetic testing is pursued in some cases, particularly when a definitive diagnosis is not possible and especially for the purpose of assessing genetic risk for couples wanting to have children. The expertise available in the clinical hematology laboratory is essential for the diagnosis of patients with hemoglobin abnormalities. Initial diagnoses are made using protein-based techniques such as electrophoresis and chromatography. Based on these findings, genetic risk to an individual's offspring can be assessed. In the setting of β-thalassemia and other β-globin disorders, coincident α-thalassemia may be difficult to diagnose, which can have potentially serious consequences. In addition, unusual forms of β-thalassemia caused by deletions in the β-globin locus cannot be definitively characterized using standard techniques. Molecular diagnostic testing has an important role in the diagnosis of hemoglobin disorders and is important in the setting of genetic counseling. Molecular testing also has a role in prenatal diagnosis to identify fetuses affected by severe hemoglobinopathies and thalassemias.

Target-allele-specific probe single-base extension (TASP-SBE): a novel MALDI-TOF-MS strategy for multi-variants analysis and its application in simultaneous detection of α-/β-thalassemia mutations

Single-nucleotide variants (SNVs) and copy number variations (CNVs) are the most common genomic variations that cause phenotypic diversity and genetic disorders. MALDI-TOF-MS is a rapid and cost-effective technique for multi-variant genotyping, but it is challenging to efficiently detect CNVs and clustered SNVs, especially to simultaneously detect CNVs and SNVs in one reaction. Herein, a novel strategy termed Target-Allele-Specific Probe Single-Base Extension (TASP-SBE) was devised to efficiently detect CNVs and clustered SNVs with MALDI-TOF-MS. By comprehensive use of traditional SBE and TASP-SBE strategies, a MALDI-TOF-MS assay was also developed to simultaneously detect 28 α-/β-thalassemia mutations in a single reaction system, including 4 α-thalassemia deletions, 3 HBA and 21 HBB SNVs. The results showed that all 28 mutations were sensitively identified, and the CNVs of HBA/HBB genes were also accurately analyzed based on the ratio of peak height (RPH) between the target allele and reference gene. The double-blind evaluation results of 989 thalassemia carrier samples showed a 100% concordance of this assay with other methods. In conclusion, a one-tube MALDI-TOF-MS assay was developed to simultaneously genotype 28 thalassemia mutations. This novel TASP-SBE was also verified a practicable strategy for the detection of CNVs and clustered SNVs, providing a feasible approach for multi-variants analysis with MALDI-TOF-MS technique.

A MALDI-TOF mass spectrometry-based haemoglobin chain quantification method for rapid screen of thalassaemia

BACKGROUND

Thalassaemia is one of the most common inherited monogenic diseases worldwide with a heavy global health burden. Considering its high prevalence in low and middle-income countries, a cheap, accurate and high-throughput screening test of thalassaemia prior to a more expensive confirmatory diagnostic test is urgently needed.

METHODS

In this study, we constructed a machine learning model based on MALDI-TOF mass spectrometry quantification of haemoglobin chains in blood, and for the first time, evaluated its diagnostic efficacy in 674 thalassaemia (including both asymptomatic carriers and symptomatic patients) and control samples collected in three hospitals. Parameters related to haemoglobin imbalance (α-globin, β-globin, γ-globin, α/β and α-β) were used for feature selection before classification model construction with 8 machine learning methods in cohort 1 and further model efficiency validation in cohort 2.

RESULTS

The logistic regression model with 5 haemoglobin peak features achieved good classification performance in validation cohort 2 (AUC 0.99, 95% CI 0.98-1, sensitivity 98.7%, specificity 95.5%). Furthermore, the logistic regression model with 6 haemoglobin peak features was also constructed to specifically identify β-thalassaemia (AUC 0.94, 95% CI 0.91-0.97, sensitivity 96.5%, specificity 87.8% in validation cohort 2).

CONCLUSIONS

For the first time, we constructed an inexpensive, accurate and high-throughput classification model based on MALDI-TOF mass spectrometry quantification of haemoglobin chains and demonstrated its great potential in rapid screening of thalassaemia in large populations.Key messagesThalassaemia is one of the most common inherited monogenic diseases worldwide with a heavy global health burden.We constructed a machine learning model based on MALDI-TOF mass spectrometry quantification of haemoglobin chains to screen for thalassaemia.

Development of DNA controls for detection of β-thalassemia mutations commonly found in Asian

INTRODUCTION

Several DNA-based approaches including a reverse dot-blot hybridization (RDB) have been established for detection of β-thalassemia genotypes to provide accurate genetic counseling and prenatal diagnosis for prevention and control of severe β-thalassemia. However, one of major concerns of these techniques is a risk of misdiagnosis due to a lack of DNA controls. Here, we constructed positive DNA controls for β-thalassemia genotyping in order to ensure that all steps in the analysis are performed properly.

METHODS

Four recombinant β-globin plasmids, including a normal sequence and three different mutant panels covering 10 common β-thalassemia mutations in Asia, were constructed by a conventional cloning method followed by sequential rounds of site-directed mutagenesis. These positive DNA controls were further validated by RDB analysis.

RESULTS

We demonstrated the applicability of established positive DNA controls for β-thalassemia genotyping in terms of accuracy and reproducibility by RDB analysis. We further combined three mutant β-globin plasmids into a single positive control, which showed positive signals for both normal and mutant probes of all tested mutations. Therefore, only two positive DNA controls, normal and combined mutant β-globin plasmids, are required for detecting 10 common β-thalassemia mutations by RDB, reducing the cost, time, and efforts in the routine diagnosis.

CONCLUSION

The β-globin DNA controls established here provide efficient alternatives to a conventional DNA source from peripheral blood, which is more difficult to obtain. They also provide a platform for future development of β-globin plasmid controls with other mutations, which can also be suitable for other DNA-based approaches.

Polymorphisms of the TNF Gene and Three Susceptibility Loci Are Associated with Crohn's Disease and Perianal Fistula Crohn's Disease: A Study among the Han Population from South China

Background

Although 90 susceptibility loci of Crohn’s disease (CD) have been confirmed in the Asian population, susceptibility genes for perianal fistula of CD (pCD) in this population remain unknown. This study explored susceptibility genes for CD and pCD in the Han population from South China.

Material/Methods

In total, 490 patients diagnosed with CD between July 2012 and June 2016 at the Sixth Affiliated Hospital of Sun Yat-sen University were included and divided into the CD group (n=240) and the pCD group (n=250). The healthy control group was composed of 260 volunteers. Peripheral blood samples were taken, and single nucleotide polymorphism (SNP) locus sequencing was used to screen for susceptibility loci. SNPs were sequenced using matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

Results

Nine SNPs in TNFSF1 on chromosome 9 were associated with CD. Among them, the rs6478106 locus is a risk locus for CD. The distribution frequency of the T allele of the rs6478106 SNP was significantly different between cases and controls (32.49% versus 18.27%, P<0.001). Rs72553867, located in the IRGM gene on chromosome 5, rs4409764, located in the NKX2–3 gene on chromosome 10, and rs3731772, located in the AOX1 gene on chromosome 2, were susceptibility factors for pCD. Nine SNPs located in TNFSF15 on chromosome 9 were related to CD in Han individuals from Southern China.

Conclusions

The rs6478106 T allele is associated with the risk of CD in the investigated population. SNPs rs72553867 (IRGM gene), rs4409764 (NKX2–3 gene), and rs3731772 (AOX1 gene) increase the risk of pCD.

Identification of Trypanosomatids by detecting Single Nucleotide Fingerprints using DNA analysis by dynamic chemistry with MALDI-ToF

Protozoan parasites of the Trypanosomatidae family can cause devastating diseases in humans and animals, such as Human African Trypanosomiasis or Sleeping Sickness, Chagas disease and Leishmaniasis. Currently, there are molecular assays for detecting parasitic infections and their post-treatment monitoring based on nucleic acid amplification, but there are still certain limitations which limit the development of assays that can detect and discriminate between parasite infections with a single test. Here, we present the development of a novel molecular assay for the rapid identification of Trypanosomatids, integrating DNA analysis by dynamic chemistry in conjunction with Matrix-Assisted Laser Desorption Ionization - Time-of-Flight Mass Spectrometry (MALDI-ToF). Differentiation of Trypanosoma cruzi, Trypanosoma brucei and Leishmania spp. is now possible using a single reaction tube, and enables rapid identification of Trypanosomatids. The test is based on a singleplex PCR, using a specific primer pair that amplifies a 155 base pair segment of the 28S ribosomal RNA gene, within a conserved homology region of Trypanosomatidae species. Amplified fragments are analysed by dynamic chemistry using two abasic PNA probes and the four reactive nucleobases - containing an aldehyde functional group - with MALDI-ToF to identify unique molecular patterns created by each specie due to their single base differences (Single Nucleotide Fingerprint 'SNF') in this highly homologous region. This novel assay offers the possibility to expand routine diagnostic testing for Trypanosomatids, and monitoring of therapeutic responses to these infectious diseases.

Molecular Diagnosis of Thalassemias and Hemoglobinopathies: An ACLPS Critical Review

OBJECTIVES

To describe the use of molecular diagnostic techniques for patients with hemoglobin disorders.

METHODS

A clinical scenario is presented in which molecular diagnosis is important for genetic counseling. Globin disorders, techniques for their diagnosis, and the role of molecular genetic testing in managing patients with these disorders are described in detail.

RESULTS

Hemoglobin disorders, including thalassemias and hemoglobinopathies, are among the commonest genetic diseases, and the clinical laboratory is essential for the diagnosis of patients with these abnormalities. Most disorders can be diagnosed with protein-based techniques such as electrophoresis and chromatography. Since severe syndromes can result due to inheritance of combinations of globin genetic disorders, genetic counseling is important to prevent adverse outcomes. Protein-based methods cannot always detect potentially serious thalassemia disorders; in particular, α-thalassemia may be masked in the presence of β-thalassemia. Deletional forms of β-thalassemia are also sometimes difficult to diagnose definitively with standard methods.

CONCLUSIONS

Molecular genetic testing serves an important role in identifying individuals carrying thalassemia traits that can cause adverse outcomes in offspring. Furthermore, prenatal genetic testing can identify fetuses with severe globin phenotypes.

Inferring population structure and relationship using minimal independent evolutionary markers in Y-chromosome: a hybrid approach of recursive feature selection for hierarchical clustering

Inundation of evolutionary markers expedited in Human Genome Project and 1000 Genome Consortium has necessitated pruning of redundant and dependent variables. Various computational tools based on machine-learning and data-mining methods like feature selection/extraction have been proposed to escape the curse of dimensionality in large datasets. Incidentally, evolutionary studies, primarily based on sequentially evolved variations have remained un-facilitated by such advances till date. Here, we present a novel approach of recursive feature selection for hierarchical clustering of Y-chromosomal SNPs/haplogroups to select a minimal set of independent markers, sufficient to infer population structure as precisely as deduced by a larger number of evolutionary markers. To validate the applicability of our approach, we optimally designed MALDI-TOF mass spectrometry-based multiplex to accommodate independent Y-chromosomal markers in a single multiplex and genotyped two geographically distinct Indian populations. An analysis of 105 world-wide populations reflected that 15 independent variations/markers were optimal in defining population structure parameters, such as F_ST, molecular variance and correlation-based relationship. A subsequent addition of randomly selected markers had a negligible effect (close to zero, i.e. 1 × 10⁻³) on these parameters. The study proves efficient in tracing complex population structures and deriving relationships among world-wide populations in a cost-effective and expedient manner.

Defining the disease liability of variants in the cystic fibrosis transmembrane conductance regulator gene

Allelic heterogeneity in disease-causing genes presents a substantial challenge to the translation of genomic variation to clinical practice. Few of the almost 2,000 variants in the cystic fibrosis transmembrane conductance regulator (CFTR) gene have empirical evidence that they cause cystic fibrosis. To address this gap, we collected both genotype and phenotype data for 39,696 cystic fibrosis patients in registries and clinics in North America and Europe. Among these patients, 159 CFTR variants had an allele frequency of ≥0.01%. These variants were evaluated for both clinical severity and functional consequence with 127 (80%) meeting both clinical and functional criteria consistent with disease. Assessment of disease penetrance in 2,188 fathers of cystic fibrosis patients enabled assignment of 12 of the remaining 32 variants as neutral while the other 20 variants remained indeterminate. This study illustrates that sourcing data directly from well-phenotyped subjects can address the gap in our ability to interpret clinically-relevant genomic variation.

Efficient detection of Mediterranean β-thalassemia mutations by multiplex single-nucleotide primer extension

β-Thalassemias and abnormal hemoglobin variants are among the most common hereditary abnormalities in humans. Molecular characterization of the causative genetic variants is an essential part of the diagnostic process. In geographic areas with high hemoglobinopathy prevalence, such as the Mediterranean region, a limited number of genetic variants are responsible for the majority of hemoglobinopathy cases. Developing reliable, rapid and cost-effective mutation-specific molecular diagnostic assays targeting particular populations greatly facilitates routine hemoglobinopathy investigations. We developed a one-tube single-nucleotide primer extension assay for the detection of eight common Mediterranean β-thalassemia mutations: Codon 5 (-CT); CCT(Pro)->C–, Codon 6 (-A); GAG(Glu)->G-G, Codon 8 (-AA); AAG(Lys)->–G, IVS-I-1 (G->A), IVS-I-6 (T->C), IVS-I-110 (G->A), Codon 39 (C->T), and IVS-II-745 (C->G), as well as the hemoglobin S variant beta 6(A3) Glu>Val. We validated the new assay using previously genotyped samples obtaining 100% agreement between independent genotyping methods. Our approach, applicable in a range of Mediterranean countries, offers a combination of high accuracy and rapidity exploiting standard techniques and widely available equipment. It can be further adapted to particular populations by including/excluding assayed mutations. We facilitate future modifications by providing detailed information on assay design.

Development of a fibrous DNA chip for cost-effective β-thalassemia genotyping

β-thalassemia is one of the most common genetic disorders worldwide. Concerted efforts are being made to prevent the disease, as the medical and economic burden of thalassemia represents a major public health problem. The molecular diagnosis of the β-globin mutations that cause the disease currently involves a combination of classic methodologies. A microarray-based assay for parallel one-shot detection of mutations has been developed, but the assay remains too expensive for routine application. We developed a cost-effective plastic fiber-based DNA chip for the fast and reliable detection of 25 types of β-thalassemia mutations. Assay conditions were established and genotyping was successfully performed on a genomic sample from a β-thalassemia patient. Our data show that this β-thalassemia genotyping chip is an advantageous platform for mass genotyping because of its low cost, rapid results, and reliability.

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

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

Fetal sex determination using circulating cell-free fetal DNA (ccffDNA) at 11 to 13 weeks of gestation

OBJECTIVE

To examine the performance of a mass spectrometry-based detection platform using three Y-chromosome sequences for fetal sex determination from circulating cell-free fetal DNA (ccffDNA) in maternal blood in the first trimester of pregnancy.

METHODS

We extracted ccffDNA for the determination of fetal sex from stored maternal plasma obtained at 11 to 13 weeks' gestation from singleton pregnancies with documented fetal gender. Mass spectrometry was used to examine 236 specimens for the presence of three Y-chromosome sequences (SRY, DBY and TTTY2). The sample was classified as male, female or inconclusive depending on the detection of three, one/none and two sequences, respectively.

RESULTS

Three (1.3%) of the 236 cases were classified as invalid due to the absence of a well-defined spectral peak for TGIF and 22 (9.3%) were reported as inconclusive. In the 211 cases with a valid result, the fetal sex was correctly identified in 90 of 91 male babies and 119 of 120 female babies giving an accuracy of 99.1% and sensitivity and specificity for prediction of male fetuses of 98.9 and 99.2%, respectively.

CONCLUSION

Fetal sex determination can be accurately determined from maternal ccffDNA in the first trimester of pregnancy using mass spectrometry analysis.

The suitability of matrix assisted laser desorption/ionization time of flight mass spectrometry in a laboratory developed test using cystic fibrosis carrier screening as a model

We designed a laboratory developed test (LDT) by using an open platform for mutation/polymorphism detection. Using a 108-member (mutation plus variant) cystic fibrosis carrier screening panel as a model, we completed the last phase of LDT validation by using matrix-assisted laser desorption/ionization time of flight mass spectrometry. Panel customization was accomplished via specific amplification primer and extension probe design. Amplified genomic DNA was subjected to allele specific, single base extension endpoint analysis by mass spectrometry for inspection of the cystic fibrosis transmembrane regulator gene (NM_000492.3). The panel of mutations and variants was tested against 386 blinded samples supplied by "authority" laboratories highly experienced in cystic fibrosis transmembrane regulator genotyping; >98% concordance was observed. All discrepant and discordant results were resolved satisfactorily. Taken together, these results describe the concluding portion of the LDT validation process and the use of mass spectrometry to detect a large number of complex reactions within a single run as well as its suitability as a platform appropriate for interrogation of scores to hundreds of targets.