Humu-2014-0022 Invited Commentary
The Challenge for the Next Generation of Medical Geneticists
Thierry Frebourg Department of Genetics, Rouen University Hospital and Inserm U1079, Institute for Research and Innovation in Biomedicine, Rouen University, France
Correspondence to: Thierry Frebourg, Department of Genetics, Rouen University Hospital and Inserm U1079, Faculty of Medicine, 22 boulevard Gambetta, 76183 Rouen Cedex, France; Phone: +33 2 32 88 81 82; Fax: +33 2 32 88 80 80; E-mail: [email protected]
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/humu.22592. This article is protected by copyright. All rights reserved.
1
Abstract
Next Generation Sequencing (NGS) has allowed a tremendous progress in the characterization of the molecular bases of genetic diseases and the last annual ASHG meeting has highlighted the implementation of whole-exome sequencing in medical genetics. Several investigators suggest that it should be medically relevant for each individual to have the exome sequenced. These perspectives do not take into account the complexity of genetic variation interpretation and of genetic determinism of human diseases: an important limiting step of targeted analyses of gene(s) involved in Mendelian diseases is already the interpretation of variants of unknown significance; most of the 20,000 SNVs present in each exome, even those having a very low allelic frequency, are not deleterious; the genetic determinism of the majority of human diseases involves either a combination of numerous genetic variations, each conferring a slightly increased risk, or rare genetic variations with a strong effect, but the demonstration of their involvement in diseases is particularly challenging. The challenge for the next generation of medical geneticists will be to integrate the technological power of NGS technologies, the complexity of genome interpretation, the importance of phenotyping before genotyping and the guidelines of medical genetics raised in the pre-NGS era.
KEY WORDS: NGS, exome, WES, WGS, genetic variation, GWAS, CNV, VUS, interpretation
This article is protected by copyright. All rights reserved.
2
Next Generation Sequencing (NGS) represents an unprecedented technological revolution whose implications in human biology and medicine are considerable [for review, see Koboldt et al., 2013]. While the human DNA sequencing project completed in 2003 required 10 years of international collaborations and 2.7 billions of dollars, it is now possible to sequence on bench platforms, routinely within a few weeks and soon within a few days, the 34 Mb human exome, corresponding to the coding part and 1.2% of the genome, for less than 2000 dollars. After whole exome sequencing (WES), the next step, coming soon, will be whole genome sequencing (WGS). The challenge for the medical geneticists is now to integrate into their practice these technological revolutions for the benefit of patients. Since 2009, NGS has facilitated tremendous progress in the characterization of the molecular bases of genetic diseases [Ng et al., 2009; Boycott et al., 2013], even from a limited number of patients. These studies used different strategies based on the comparison of exomes from several affected subjects presenting the same disease but issued from different families,
or from affected relatives within a single family, or from a patient and the
unaffected parents in order to identify de novo mutation. The last annual meeting of the American Society of Human Genetics in October 2013 has highlighted the implementation in different countries of whole-exome sequencing (WES) in medical genetics. The experience of the Baylor College of Medicine in Houston, reporting WES in 250 probands suspected to present a genetic disorder and previously phenotyped by physicians but without diagnosis, indicates that WES allows the identification of the genetic defect in 25% of the patients [Yang et al., 2013]. A first economical evaluation of WES has shown that this strategy, in patients without diagnosis after first phenotypic evaluation and targeted genetic analyses, is economically beneficial [Shashi et al., 2013]. In the United-Kingdom, combining the phenotypic expertise of a nationwide network of clinical geneticists and the sequencing
This article is protected by copyright. All rights reserved.
3
power of the Wellcome Trust Sanger Institute allowed WES of 1100 deeply phenotyped probands and their parents, in the context of the Deciphering Developmental Disorders project (https://decipher.sanger.ac.uk/ [Bragin et al., 2014]. This has facilitated molecular diagnosis in approximately 20% of the children (as noted by Hurles and colleagues at the 2013 ASHG annual meeting).. In contrast, several investigators are pushing the idea that, beyond genetic diseases, it should be useful and medically relevant for each individual, even without personal or familial history suggesting a genetic disease, to have the exome sequenced in order to allow the estimation of disease risk and the prevention and early diagnosis of diseases (http://www.genomes2people.org/the-medseq-project). Some private companies even claim that every individual could have their genome on smartphones and electronic tablets. These perspectives are in contradiction with what we have learned in medical genetics over the last 20 years. One critical rule of medical genetics, highlighted by professionals performing genetic counseling, is to deliver faithful information to the patient, prior to the test. The medical impact for the patient and the family of the identification of a mutation conferring an increased risk for a disease, the degree of the risk and the significance of negative results should be clearly explained, both in the pre-test counseling session but again in the postcounseling session. The psychological impact should be anticipated and, if necessary, appropriate psychological follow-up should be offered. Furthermore, in the NGS era, the main challenge is no longer the detection of genetic variations but their interpretation. First, even using conventional methods such as PCR amplification and Sanger sequencing, one of the most important limiting steps for medical genetics laboratories performing focused analyses of gene(s) involved in Mendelian diseases is the interpretation of a large fraction of genetic variants designated “variants of unknown significance” or VUS. In some cases, interpretation of these VUS can be provided by segregation analysis in
This article is protected by copyright. All rights reserved.
4
families including multiple affected members or the de novo occurrence of the variation in the affected subject, however, in many cases the interpretation of VUS remains challenging and these VUS cannot be used for the clinical management of patients and families. This problem is illustrated by the molecular diagnoses of hereditary breast and ovarian cancer and Lynch syndrome, which are the two most common forms of inherited cancers. VUS identified in patients within BRCA1/BRCA2 or MMR genes represent approximately 30% of the variations detected in patients and these genes became the paradigm of VUS interpretation challenge in medical genetics. International consortia, such as Enigma (Evidence-based
Network
for
the
Interpretation
of
Germline
Mutant
Alleles;
http://enigmaconsortium.org/) or Insight (International Society for Hereditary Gastrointestinal tumors; http://www.insight-group.org/criteria/), have been raised in order to classify the VUS according to scores integrating segregation of the VUS with the disease, its recurrence, the allelic frequency in a control population, the conservation of the amino-acid, the predicted effect on protein function or RNA splicing and results of functional assays [Thompson et al., 2013]. Thanks to this international effort and will to share clinical and biological data, clinicians and molecular geneticists are performing a tedious but necessary work for the benefit of the patients, allowing a progressive re-classification of VUS as deleterious changes or neutral variations. The second challenge of variant interpretation is the extent of human DNA variability unmasked by NGS. Since the first exomes performed in humans in 2009 [Ng et al., 2009], we know that each individual exome, corresponding only to 1.2% of the genome, contains approximately 20,000 Single Nucleotide Variations (SNVs), 500 having a very low allelic frequency, some of these SNVs being private or specific of a single individual. Most of these SNVs are not deleterious. This has been recently demonstrated by a study performed on 1000 exomes and focused on 114 genes associated with medically actionable genetic diseases,
This article is protected by copyright. All rights reserved.
5
showing that among the 239 variants classified as "disease causing" in Human Gene Mutation Database, only 18 were likely to be pathogenic [Dorschner et al., 2013]. The American College of Medical Genetics and Genomics (ACMG) has recently highlighted the particularly challenging question of incidental findings, defined as genetic variations identified by genomic sequencing but not related to the disease being investigated [Green et al., 2013]. The ACMG proposed to report only variations involved in disorders for which preventive measures and/or treatments are available and to dichotomize these incidental findings into known pathogenic and expected pathogenic variations. Third, we have learned that the genetic determinism of complex diseases, which represent the majority of human diseases, is indeed complex [Koboldt et al., 2013]. The initial hypothesis was to consider that the majority of common diseases involve a complex combination of numerous genetic variations present in the general population, each single variation conferring only a slightly increased risk, in the magnitude of 1.1-1.2. These genetic variations, detected by genome-wide association studies (GWAS) based on the comparison of allelic frequencies between thousands of cases and controls, have no medical value for a single individual. The alternative hypothesis, amplified since the NGS development, is that the heritability of many complex diseases may be due to rare genetic variations with a strong effect [Schork et al., 2009]. The demonstration of the involvement of these rare genetic variations in diseases is particularly challenging and requires new statistical tests, grouping or collapsing these variations usually by gene, in order to increase statistical power. Furthermore the interpretation of these rare variations is hampered by the fact that their allelic frequency is not stratified according to population groups, the only available estimations deriving from the 1000 genome project which covers 14 populations world-wide or from the ESP (Exome Sequencing Project) consortium, in which the American population has been dichotomized in two groups from European and African origin, respectively.
This article is protected by copyright. All rights reserved.
6
Therefore, it is of upmost importance that the genetic community should inform patients, citizens, policy makers and even health professional of the limits of the information delivered by genomic sequencing in isolation; genome analysis without phenotyping will have limited medical value. WES should be used to answer a clinical question and healthcare professionals should possess the requisite expertise before recommending WES testing, interpreting the results, and offering appropriate treatment options after the results. The challenge of genetic variation interpretation will increase when whole genome sequencing will be implemented in medical laboratories. Furthermore, for the patients, uncertainty on the biological significance of genetic variations is likely to have negative psychological impacts. NGS represents a remarkable progress in medical genetics only if it respects the guidelines of medical genetics and benefits from interactions with clinicians. If not, we will move to the slippery slope of genomic reductionism based on a misunderstanding of the genetic complexity. The challenge for the next generation of medical geneticists will be to integrate the technological power of NGS technologies, the complexity of genomic analysis and the guidelines of medical genetics raised in the pre-NGS era.
ACKNOWLEDGMENTS The author thanks Mario Tosi for critical reading of the manuscript. Disclosure statement: The author declares no conflict of interest.
This article is protected by copyright. All rights reserved.
7
REFERENCES Boycott KM, Vanstone MR, Bulman DE, MacKenzie AE.Rare-disease genetics in the era of next-generation sequencing: discovery to translation. 2013. Nat Rev Genetics14: 681-691. Bragin E, Chatzimichali EA, Wright CF, Hurles ME, Firth HV, Bevan AP, Swaminathan GJ. 2014. DECIPHER: database for the interpretation of phenotype-linked plausibly pathogenic sequence and copy-number variation. Nucleic Acids Res 42: D993-D1000. Dorschner MO, Amendola LM, Turner EH, Robertson PD, Shirts BH, Gallego CJ, Bennett RL, Jones KL, Tokita MJ, Bennett JT, Kim JH, Rosenthal EA, et al. 2013. Actionable, Pathogenic Incidental Findings in 1,000 Participants' Exomes. Am J Hum Genet 93: 631-640. Green RC, Berg JS, Grody WW, Kalia SS, Korf BR, Martin CL, McGuire AL, Nussbaum RL, O’Daniel JM, Ormond KE, Rehm HL, Watson MS, et al. 2013. ACMG recommendations for reporting of incidental findings in clinical exome and genome sequencing. Genet Med 15: 565–574. Koboldt DC, Steinberg KM, Larson DE, Wilson RK, Mardis ER. 2013. The next-generation sequencing revolution and its impact on genomics. Cell 155: 27-38. Ng SB, Turner EH, Robertson PD, Flygare SD, Bigham AW, Lee C, Shaffer T, Wong M, Bhattacharjee A, Eichler EE, Bamshad M, Nickerson DA, Shendure J. 2009. Targeted capture and massively parallel sequencing of 12 human exomes. Nature 461: 272-276. Schork NJ, Murray SS, Frazer KA, Topol EJ. 2009. Common vs. rare allele hypotheses for complex diseases. Curr Opin Genet Dev 19: 212-219. Shashi V, McConkie-Rosell A, Rosell B, Schoch K, Vellore K, McDonald M, Jiang YH, Xie P, Need A, Goldstein DG. 2013. The utility of the traditional medical genetics
This article is protected by copyright. All rights reserved.
8
diagnostic evaluation in the context of next-generation sequencing for undiagnosed genetic disorders. Genet Med 16:176-182. Thompson BA, Spurdle AB, Plazzer JP, Greenblatt MS, Akagi K, Al-Mulla F, Bapat B, Bernstein I, Capellá G, den Dunnen JT, du Sart D, Fabre A ,et al. Application of a 5tiered scheme for standardized classification of 2,360 unique mismatch repair gene variants in the InSiGHT locus-specific database. Nat Genet. 2014; 46: 107-15. Yang Y, Muzny DM, Reid JG, Bainbridge MN, Willis A, Ward PA, Braxton A, Beuten J, Xia F, Niu Z, Hardison M, Person R, et al. 2013. Clinical whole-exome sequencing for the diagnosis of mendelian disorders. N Engl J Med 369: 1502-1511. Zawati MH, Parry D, Thorogood A, Nguyen MT, Boycott KM, Rosenblatt D, Knoppers BM. 2014. Reporting results from whole-genome and whole-exome sequencing in clinical practice: a proposal for Canada? J Med Genet 51: 68-70.
This article is protected by copyright. All rights reserved.
9
The Challenge for the Next Generation of Medical Geneticists
Thierry Frebourg Department of Genetics, Rouen University Hospital and Inserm U1079, Institute for Research and Innovation in Biomedicine, Rouen University, France
Correspondence to: Thierry Frebourg, Department of Genetics, Rouen University Hospital and Inserm U1079, Faculty of Medicine, 22 boulevard Gambetta, 76183 Rouen Cedex, France; Phone: +33 2 32 88 81 82; Fax: +33 2 32 88 80 80; E-mail: [email protected]
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/humu.22592. This article is protected by copyright. All rights reserved.
1
Abstract
Next Generation Sequencing (NGS) has allowed a tremendous progress in the characterization of the molecular bases of genetic diseases and the last annual ASHG meeting has highlighted the implementation of whole-exome sequencing in medical genetics. Several investigators suggest that it should be medically relevant for each individual to have the exome sequenced. These perspectives do not take into account the complexity of genetic variation interpretation and of genetic determinism of human diseases: an important limiting step of targeted analyses of gene(s) involved in Mendelian diseases is already the interpretation of variants of unknown significance; most of the 20,000 SNVs present in each exome, even those having a very low allelic frequency, are not deleterious; the genetic determinism of the majority of human diseases involves either a combination of numerous genetic variations, each conferring a slightly increased risk, or rare genetic variations with a strong effect, but the demonstration of their involvement in diseases is particularly challenging. The challenge for the next generation of medical geneticists will be to integrate the technological power of NGS technologies, the complexity of genome interpretation, the importance of phenotyping before genotyping and the guidelines of medical genetics raised in the pre-NGS era.
KEY WORDS: NGS, exome, WES, WGS, genetic variation, GWAS, CNV, VUS, interpretation
This article is protected by copyright. All rights reserved.
2
Next Generation Sequencing (NGS) represents an unprecedented technological revolution whose implications in human biology and medicine are considerable [for review, see Koboldt et al., 2013]. While the human DNA sequencing project completed in 2003 required 10 years of international collaborations and 2.7 billions of dollars, it is now possible to sequence on bench platforms, routinely within a few weeks and soon within a few days, the 34 Mb human exome, corresponding to the coding part and 1.2% of the genome, for less than 2000 dollars. After whole exome sequencing (WES), the next step, coming soon, will be whole genome sequencing (WGS). The challenge for the medical geneticists is now to integrate into their practice these technological revolutions for the benefit of patients. Since 2009, NGS has facilitated tremendous progress in the characterization of the molecular bases of genetic diseases [Ng et al., 2009; Boycott et al., 2013], even from a limited number of patients. These studies used different strategies based on the comparison of exomes from several affected subjects presenting the same disease but issued from different families,
or from affected relatives within a single family, or from a patient and the
unaffected parents in order to identify de novo mutation. The last annual meeting of the American Society of Human Genetics in October 2013 has highlighted the implementation in different countries of whole-exome sequencing (WES) in medical genetics. The experience of the Baylor College of Medicine in Houston, reporting WES in 250 probands suspected to present a genetic disorder and previously phenotyped by physicians but without diagnosis, indicates that WES allows the identification of the genetic defect in 25% of the patients [Yang et al., 2013]. A first economical evaluation of WES has shown that this strategy, in patients without diagnosis after first phenotypic evaluation and targeted genetic analyses, is economically beneficial [Shashi et al., 2013]. In the United-Kingdom, combining the phenotypic expertise of a nationwide network of clinical geneticists and the sequencing
This article is protected by copyright. All rights reserved.
3
power of the Wellcome Trust Sanger Institute allowed WES of 1100 deeply phenotyped probands and their parents, in the context of the Deciphering Developmental Disorders project (https://decipher.sanger.ac.uk/ [Bragin et al., 2014]. This has facilitated molecular diagnosis in approximately 20% of the children (as noted by Hurles and colleagues at the 2013 ASHG annual meeting).. In contrast, several investigators are pushing the idea that, beyond genetic diseases, it should be useful and medically relevant for each individual, even without personal or familial history suggesting a genetic disease, to have the exome sequenced in order to allow the estimation of disease risk and the prevention and early diagnosis of diseases (http://www.genomes2people.org/the-medseq-project). Some private companies even claim that every individual could have their genome on smartphones and electronic tablets. These perspectives are in contradiction with what we have learned in medical genetics over the last 20 years. One critical rule of medical genetics, highlighted by professionals performing genetic counseling, is to deliver faithful information to the patient, prior to the test. The medical impact for the patient and the family of the identification of a mutation conferring an increased risk for a disease, the degree of the risk and the significance of negative results should be clearly explained, both in the pre-test counseling session but again in the postcounseling session. The psychological impact should be anticipated and, if necessary, appropriate psychological follow-up should be offered. Furthermore, in the NGS era, the main challenge is no longer the detection of genetic variations but their interpretation. First, even using conventional methods such as PCR amplification and Sanger sequencing, one of the most important limiting steps for medical genetics laboratories performing focused analyses of gene(s) involved in Mendelian diseases is the interpretation of a large fraction of genetic variants designated “variants of unknown significance” or VUS. In some cases, interpretation of these VUS can be provided by segregation analysis in
This article is protected by copyright. All rights reserved.
4
families including multiple affected members or the de novo occurrence of the variation in the affected subject, however, in many cases the interpretation of VUS remains challenging and these VUS cannot be used for the clinical management of patients and families. This problem is illustrated by the molecular diagnoses of hereditary breast and ovarian cancer and Lynch syndrome, which are the two most common forms of inherited cancers. VUS identified in patients within BRCA1/BRCA2 or MMR genes represent approximately 30% of the variations detected in patients and these genes became the paradigm of VUS interpretation challenge in medical genetics. International consortia, such as Enigma (Evidence-based
Network
for
the
Interpretation
of
Germline
Mutant
Alleles;
http://enigmaconsortium.org/) or Insight (International Society for Hereditary Gastrointestinal tumors; http://www.insight-group.org/criteria/), have been raised in order to classify the VUS according to scores integrating segregation of the VUS with the disease, its recurrence, the allelic frequency in a control population, the conservation of the amino-acid, the predicted effect on protein function or RNA splicing and results of functional assays [Thompson et al., 2013]. Thanks to this international effort and will to share clinical and biological data, clinicians and molecular geneticists are performing a tedious but necessary work for the benefit of the patients, allowing a progressive re-classification of VUS as deleterious changes or neutral variations. The second challenge of variant interpretation is the extent of human DNA variability unmasked by NGS. Since the first exomes performed in humans in 2009 [Ng et al., 2009], we know that each individual exome, corresponding only to 1.2% of the genome, contains approximately 20,000 Single Nucleotide Variations (SNVs), 500 having a very low allelic frequency, some of these SNVs being private or specific of a single individual. Most of these SNVs are not deleterious. This has been recently demonstrated by a study performed on 1000 exomes and focused on 114 genes associated with medically actionable genetic diseases,
This article is protected by copyright. All rights reserved.
5
showing that among the 239 variants classified as "disease causing" in Human Gene Mutation Database, only 18 were likely to be pathogenic [Dorschner et al., 2013]. The American College of Medical Genetics and Genomics (ACMG) has recently highlighted the particularly challenging question of incidental findings, defined as genetic variations identified by genomic sequencing but not related to the disease being investigated [Green et al., 2013]. The ACMG proposed to report only variations involved in disorders for which preventive measures and/or treatments are available and to dichotomize these incidental findings into known pathogenic and expected pathogenic variations. Third, we have learned that the genetic determinism of complex diseases, which represent the majority of human diseases, is indeed complex [Koboldt et al., 2013]. The initial hypothesis was to consider that the majority of common diseases involve a complex combination of numerous genetic variations present in the general population, each single variation conferring only a slightly increased risk, in the magnitude of 1.1-1.2. These genetic variations, detected by genome-wide association studies (GWAS) based on the comparison of allelic frequencies between thousands of cases and controls, have no medical value for a single individual. The alternative hypothesis, amplified since the NGS development, is that the heritability of many complex diseases may be due to rare genetic variations with a strong effect [Schork et al., 2009]. The demonstration of the involvement of these rare genetic variations in diseases is particularly challenging and requires new statistical tests, grouping or collapsing these variations usually by gene, in order to increase statistical power. Furthermore the interpretation of these rare variations is hampered by the fact that their allelic frequency is not stratified according to population groups, the only available estimations deriving from the 1000 genome project which covers 14 populations world-wide or from the ESP (Exome Sequencing Project) consortium, in which the American population has been dichotomized in two groups from European and African origin, respectively.
This article is protected by copyright. All rights reserved.
6
Therefore, it is of upmost importance that the genetic community should inform patients, citizens, policy makers and even health professional of the limits of the information delivered by genomic sequencing in isolation; genome analysis without phenotyping will have limited medical value. WES should be used to answer a clinical question and healthcare professionals should possess the requisite expertise before recommending WES testing, interpreting the results, and offering appropriate treatment options after the results. The challenge of genetic variation interpretation will increase when whole genome sequencing will be implemented in medical laboratories. Furthermore, for the patients, uncertainty on the biological significance of genetic variations is likely to have negative psychological impacts. NGS represents a remarkable progress in medical genetics only if it respects the guidelines of medical genetics and benefits from interactions with clinicians. If not, we will move to the slippery slope of genomic reductionism based on a misunderstanding of the genetic complexity. The challenge for the next generation of medical geneticists will be to integrate the technological power of NGS technologies, the complexity of genomic analysis and the guidelines of medical genetics raised in the pre-NGS era.
ACKNOWLEDGMENTS The author thanks Mario Tosi for critical reading of the manuscript. Disclosure statement: The author declares no conflict of interest.
This article is protected by copyright. All rights reserved.
7
REFERENCES Boycott KM, Vanstone MR, Bulman DE, MacKenzie AE.Rare-disease genetics in the era of next-generation sequencing: discovery to translation. 2013. Nat Rev Genetics14: 681-691. Bragin E, Chatzimichali EA, Wright CF, Hurles ME, Firth HV, Bevan AP, Swaminathan GJ. 2014. DECIPHER: database for the interpretation of phenotype-linked plausibly pathogenic sequence and copy-number variation. Nucleic Acids Res 42: D993-D1000. Dorschner MO, Amendola LM, Turner EH, Robertson PD, Shirts BH, Gallego CJ, Bennett RL, Jones KL, Tokita MJ, Bennett JT, Kim JH, Rosenthal EA, et al. 2013. Actionable, Pathogenic Incidental Findings in 1,000 Participants' Exomes. Am J Hum Genet 93: 631-640. Green RC, Berg JS, Grody WW, Kalia SS, Korf BR, Martin CL, McGuire AL, Nussbaum RL, O’Daniel JM, Ormond KE, Rehm HL, Watson MS, et al. 2013. ACMG recommendations for reporting of incidental findings in clinical exome and genome sequencing. Genet Med 15: 565–574. Koboldt DC, Steinberg KM, Larson DE, Wilson RK, Mardis ER. 2013. The next-generation sequencing revolution and its impact on genomics. Cell 155: 27-38. Ng SB, Turner EH, Robertson PD, Flygare SD, Bigham AW, Lee C, Shaffer T, Wong M, Bhattacharjee A, Eichler EE, Bamshad M, Nickerson DA, Shendure J. 2009. Targeted capture and massively parallel sequencing of 12 human exomes. Nature 461: 272-276. Schork NJ, Murray SS, Frazer KA, Topol EJ. 2009. Common vs. rare allele hypotheses for complex diseases. Curr Opin Genet Dev 19: 212-219. Shashi V, McConkie-Rosell A, Rosell B, Schoch K, Vellore K, McDonald M, Jiang YH, Xie P, Need A, Goldstein DG. 2013. The utility of the traditional medical genetics
This article is protected by copyright. All rights reserved.
8
diagnostic evaluation in the context of next-generation sequencing for undiagnosed genetic disorders. Genet Med 16:176-182. Thompson BA, Spurdle AB, Plazzer JP, Greenblatt MS, Akagi K, Al-Mulla F, Bapat B, Bernstein I, Capellá G, den Dunnen JT, du Sart D, Fabre A ,et al. Application of a 5tiered scheme for standardized classification of 2,360 unique mismatch repair gene variants in the InSiGHT locus-specific database. Nat Genet. 2014; 46: 107-15. Yang Y, Muzny DM, Reid JG, Bainbridge MN, Willis A, Ward PA, Braxton A, Beuten J, Xia F, Niu Z, Hardison M, Person R, et al. 2013. Clinical whole-exome sequencing for the diagnosis of mendelian disorders. N Engl J Med 369: 1502-1511. Zawati MH, Parry D, Thorogood A, Nguyen MT, Boycott KM, Rosenblatt D, Knoppers BM. 2014. Reporting results from whole-genome and whole-exome sequencing in clinical practice: a proposal for Canada? J Med Genet 51: 68-70.
This article is protected by copyright. All rights reserved.
9
