CYP3A4 and CYP3A5 Genotyping Recommendations: A Joint Consensus Recommendation of the Association for Molecular Pathology, Clinical Pharmacogenetics Implementation Consortium, College of American Pathologists, Dutch Pharmacogenetics Working Group of the Royal Dutch Pharmacists Association, European Society for Pharmacogenomics and Personalized Therapy, and Pharmacogenomics Knowledgebase

The goals of the Association for Molecular Pathology Clinical Practice Committee's Pharmacogenomics (PGx) Working Group are to define the key attributes of pharmacogenetic alleles recommended for clinical testing and a minimum set of variants that should be included in clinical PGx genotyping assays. This document series provides recommendations for a minimum panel of variant alleles (tier 1) and an extended panel of variant alleles (tier 2) that will aid clinical laboratories when designing assays for PGx testing. The Association for Molecular Pathology PGx Working Group considered functional impact of the variant alleles, allele frequencies in multiethnic populations, the availability of reference materials, and other technical considerations for PGx testing when developing these recommendations. The goal of this Working Group is to promote standardization of PGx gene/allele testing across clinical laboratories. This document will focus on clinical CYP3A4 and CYP3A5 PGx testing that may be applied to all CYP3A4- and CYP3A5-related medications. These recommendations are not to be interpreted as prescriptive but to provide a reference guide.

Characterization of Reference Materials for CYP3A4 and CYP3A5: A (GeT-RM) Collaborative Project

Pharmacogenetic testing for CYP3A4 is increasingly provided by clinical and research laboratories; however, only a limited number of quality control and reference materials are currently available for many of the CYP3A4 variants included in clinical tests. To address this need, the Division of Laboratory Systems, CDC-based Genetic Testing Reference Material Coordination Program (GeT-RM), in collaboration with members of the pharmacogenetic testing and research communities and the Coriell Institute for Medical Research, has characterized 30 DNA samples derived from Coriell cell lines for CYP3A4. Samples were distributed to five volunteer laboratories for genotyping using a variety of commercially available and laboratory-developed tests. Sanger and next-generation sequencing were also utilized by some of the laboratories. Whole-genome sequencing data from the 1000 Genomes Projects were utilized to inform genotype. Twenty CYP3A4 alleles were identified in the 30 samples characterized for CYP3A4: CYP3A4∗4, ∗5, ∗6, ∗7, ∗8, ∗9, ∗10, ∗11, ∗12, ∗15, ∗16, ∗18, ∗19, ∗20, ∗21, ∗22, ∗23, ∗24, ∗35, and a novel allele, CYP3A4∗38. Nineteen additional samples with preexisting data for CYP3A4 or CYP3A5 were re-analyzed to generate comprehensive reference material panels for these genes. These publicly available and well-characterized materials can be used to support the quality assurance and quality control programs of clinical laboratories performing clinical pharmacogenetic testing.

TPMT and NUDT15 Genotyping Recommendations: A Joint Consensus Recommendation of the Association for Molecular Pathology, Clinical Pharmacogenetics Implementation Consortium, College of American Pathologists, Dutch Pharmacogenetics Working Group of the Royal Dutch Pharmacists Association, European Society for Pharmacogenomics and Personalized Therapy, and Pharmacogenomics Knowledgebase

The goals of the Association for Molecular Pathology Clinical Practice Committee's Pharmacogenomics (PGx) Working Group are to define the key attributes of pharmacogenetic alleles recommended for clinical testing and a minimum set of variants that should be included in clinical PGx genotyping assays. This article provides recommendations for a minimum panel of variant alleles (Tier 1) and an extended panel of variant alleles (Tier 2) that will aid clinical laboratories when designing assays for PGx testing. The Association for Molecular Pathology PGx Working Group considered the functional impact of the variant alleles, allele frequencies in multiethnic populations, the availability of reference materials, as well as other technical considerations for PGx testing when developing these recommendations. The ultimate goal of this Working Group is to promote standardization of PGx gene/allele testing across clinical laboratories. This article focuses on clinical TPMT and NUDT15 PGx testing, which may be applied to all thiopurine S-methyltransferase (TPMT) and nudix hydrolase 15 (NUDT15)-related medications. These recommendations are not to be interpreted as prescriptive, but to provide a reference guide.

Characterization of Reference Materials for TPMT and NUDT15: A GeT-RM Collaborative Project

Pharmacogenetic testing is increasingly provided by clinical and research laboratories; however, only a limited number of quality control and reference materials are currently available for many of the TPMT and NUDT15 variants included in clinical tests. To address this need, the Division of Laboratory Systems, Centers for Disease Control and Prevention-based Genetic Testing Reference Material (GeT-RM) coordination program, in collaboration with members of the pharmacogenetic testing and research communities and the Coriell Institute for Medical Research, has characterized 19 DNA samples derived from Coriell cell lines. DNA samples were distributed to four volunteer testing laboratories for genotyping using a variety of commercially available and laboratory developed tests and/or Sanger sequencing. Of the 12 samples characterized for TPMT, newly identified variants include TPMT∗2, ∗6, ∗12, ∗16, ∗21, ∗24, ∗32, ∗33, and ∗40; for the 7 NUDT15 reference material samples, newly identified variants are NUDT15∗2, ∗3, ∗4, ∗5, ∗6, and ∗9. In addition, a novel haplotype, TPMT∗46, was identified in this study. Preexisting data on an additional 11 Coriell samples, as well as some supplemental testing, were used to create comprehensive reference material panels for TPMT and NUDT15. These publicly available and well-characterized materials can be used to support the quality assurance and quality control programs of clinical laboratories performing clinical pharmacogenetic testing.

CYP2C8, CYP2C9, and CYP2C19 Characterization Using Next-Generation Sequencing and Haplotype Analysis: A GeT-RM Collaborative Project

Pharmacogenetic tests typically target selected sequence variants to identify haplotypes that are often defined by star (∗) allele nomenclature. Due to their design, these targeted genotyping assays are unable to detect novel variants that may change the function of the gene product and thereby affect phenotype prediction and patient care. In the current study, 137 DNA samples that were previously characterized by the Genetic Testing Reference Material (GeT-RM) program using a variety of targeted genotyping methods were recharacterized using targeted and whole genome sequencing analysis. Sequence data were analyzed using three genotype calling tools to identify star allele diplotypes for CYP2C8, CYP2C9, and CYP2C19. The genotype calls from next-generation sequencing (NGS) correlated well to those previously reported, except when novel alleles were present in a sample. Six novel alleles and 38 novel suballeles were identified in the three genes due to identification of variants not covered by targeted genotyping assays. In addition, several ambiguous genotype calls from a previous study were resolved using the NGS and/or long-read NGS data. Diplotype calls were mostly consistent between the calling algorithms, although several discrepancies were noted. This study highlights the utility of NGS for pharmacogenetic testing and demonstrates that there are many novel alleles that are yet to be discovered, even in highly characterized genes such as CYP2C9 and CYP2C19.

Creation of an Expert Curated Variant List for Clinical Genomic Test Development and Validation: A ClinGen and GeT-RM Collaborative Project

Modern genomic sequencing tests often interrogate large numbers of genes. Identification of appropriate reference materials for development, validation studies, and quality assurance of these tests poses a significant challenge for laboratories. It is difficult to develop and maintain expert knowledge to identify all variants that must be validated to ensure analytic and clinical validity. Additionally, it is usually not possible to procure appropriate and characterized genomic DNA reference materials containing the number and scope of variants required. To address these challenges, the Centers for Disease Control and Prevention's Genetic Testing Reference Material Program (GeT-RM) has partnered with the Clinical Genome Resource (ClinGen) to develop a publicly available list of expert curated, clinically important variants. ClinGen Variant Curation Expert Panels nominated 546 variants found in 84 disease-associated genes, including common pathogenic and difficult-to-detect variants. Variant types nominated included 346 single nucleotide variants, 104 deletions, 37 copy number variants, 25 duplications, 18 deletion-insertions, 5 inversions, 4 insertions, 2 complex rearrangements, 3 difficult-to-sequence regions, and 2 fusions. This expert-curated variant list is a resource that provides a foundation for designing comprehensive validation studies and for creating in silico reference materials for clinical genomic test development and validation.

Recommendations for Clinical CYP2D6 Genotyping Allele Selection: A Joint Consensus Recommendation of the Association for Molecular Pathology, College of American Pathologists, Dutch Pharmacogenetics Working Group of the Royal Dutch Pharmacists Association, and the European Society for Pharmacogenomics and Personalized Therapy

The goals of the Association for Molecular Pathology Clinical Practice Committee's Pharmacogenomics (PGx) Working Group are to define the key attributes of pharmacogenetic alleles recommended for clinical testing, and to determine a minimal set of variants that should be included in clinical PGx genotyping assays. This document series provides recommendations on a minimal panel of variant alleles (Tier 1) and an extended panel of variant alleles (Tier 2) that will aid clinical laboratories in designing assays for PGx testing. When developing these recommendations, the Association for Molecular Pathology PGx Working Group considered the functional impact of the variant alleles, allele frequencies in multiethnic populations, the availability of reference materials, as well as other technical considerations with regard to PGx testing. The ultimate goal of this Working Group is to promote standardization of PGx gene/allele testing across clinical laboratories. This document is focused on clinical CYP2D6 PGx testing that may be applied to all cytochrome P450 2D6-metabolized medications. These recommendations are not meant to be interpreted as prescriptive but to provide a reference guide for clinical laboratories that may be either implementing PGx testing or reviewing and updating their existing platform.

Characterization of Reference Materials with an Association for Molecular Pathology Pharmacogenetics Working Group Tier 2 Status: CYP2C9, CYP2C19, VKORC1, CYP2C Cluster Variant, and GGCX: A GeT-RM Collaborative Project

Pharmacogenetic testing is increasingly available from clinical and research laboratories. However, only a limited number of quality control and other reference materials are currently available for many of the variants that are tested. The Association for Molecular Pathology Pharmacogenetic Work Group has published a series of papers recommending alleles for inclusion in clinical testing. Several of the alleles were not considered for tier 1 because of a lack of reference materials. To address this need, the Division of Laboratory Systems, Centers for Disease Control and Prevention-based Genetic Testing Reference Material (GeT-RM) program, in collaboration with members of the pharmacogenetic testing and research communities and the Coriell Institute for Medical Research, has characterized 18 DNA samples derived from Coriell cell lines. DNA samples were distributed to five volunteer testing laboratories for genotyping using three commercially available and laboratory developed tests. Several tier 2 variants, including CYP2C9∗13, CYP2C19∗35, the CYP2C cluster variant (rs12777823), two variants in VKORC1 (rs61742245 and rs72547529) related to warfarin resistance, and two variants in GGCX (rs12714145 and rs11676382) related to clotting factor activation, were identified among these samples. These publicly available materials complement the pharmacogenetic reference materials previously characterized by the GeT-RM program and will support the quality assurance and quality control programs of clinical laboratories that perform pharmacogenetic testing.

Recommendations for Clinical Warfarin Genotyping Allele Selection: A Report of the Association for Molecular Pathology and the College of American Pathologists

The goal of the Association for Molecular Pathology (AMP) Clinical Practice Committee's AMP Pharmacogenomics (PGx) Working Group is to define the key attributes of PGx alleles recommended for clinical testing and a minimum set of variants that should be included in clinical PGx genotyping assays. This document series provides recommendations for a minimum panel of variant alleles (tier 1) and an extended panel of variant alleles (tier 2) that will aid clinical laboratories when designing assays for PGx testing. The AMP PGx Working Group considered functional impact of the variants, allele frequencies in multiethnic populations, the availability of reference materials, as well as other technical considerations for PGx testing when developing these recommendations. The ultimate goal is to promote standardization of PGx gene/allele testing across clinical laboratories. These recommendations are not to be interpreted as prescriptive but to provide a reference guide. Of note, a separate article with recommendations for CYP2C9 allele selection was previously developed by the PGx Working Group that can be applied broadly to CYP2C9-related medications. The warfarin allele recommendations in this report incorporate the previous CYP2C9 allele recommendations and additional genes and alleles that are specific to warfarin testing.

Characterization of Reference Materials for Genetic Testing of CYP2D6 Alleles: A GeT-RM Collaborative Project

Pharmacogenetic testing increasingly is available from clinical and research laboratories. However, only a limited number of quality control and other reference materials currently are available for the complex rearrangements and rare variants that occur in the CYP2D6 gene. To address this need, the Division of Laboratory Systems, CDC-based Genetic Testing Reference Material Coordination Program, in collaboration with members of the pharmacogenetic testing and research communities and the Coriell Cell Repositories (Camden, NJ), has characterized 179 DNA samples derived from Coriell cell lines. Testing included the recharacterization of 137 genomic DNAs that were genotyped in previous Genetic Testing Reference Material Coordination Program studies and 42 additional samples that had not been characterized previously. DNA samples were distributed to volunteer testing laboratories for genotyping using a variety of commercially available and laboratory-developed tests. These publicly available samples will support the quality-assurance and quality-control programs of clinical laboratories performing CYP2D6 testing.

Characterization of 108 Genomic DNA Reference Materials for 11 Human Leukocyte Antigen Loci: A GeT-RM Collaborative Project

The highly polymorphic human leukocyte antigen (HLA) genes, located in the human major histocompatibility complex, encode the class I and II antigen-presenting molecules, which are centrally involved in the immune response. HLA typing is used for several clinical applications, such as transplantation, pharmacogenetics, and diagnosis of autoimmune disease. HLA typing is highly complex because of the homology of HLA genes and pseudogenes and the extensive polymorphism in the population. The Centers for Disease Control and Prevention established the Genetic Testing Reference Materials Coordination Program (GeT-RM) in partnership with the genetics community to improve the availability of genomic DNA reference materials necessary for quality assurance of genetic laboratory testing. The GeT-RM together with three clinical laboratories and the Coriell Cell Repositories have characterized genomic DNA obtained from a panel of 108 cell lines for all HLA classic polymorphic loci: HLA-A, B, C, DRB1, DRB3, DRB4, DRB5, DQA1, DQB1, DPA1, and DPB1. The goal was to develop a publicly available and renewable source of well-characterized genomic DNA reference materials to support molecular HLA typing assay development, validation, and verification, quality control, and proficiency testing. These genomic DNA samples are publicly available from the National Institutes of General Medical Science Repository at the Coriell Cell Repositories.

Development and Characterization of Reference Materials for Genetic Testing: Focus on Public Partnerships

Characterized reference materials (RMs) are needed for clinical laboratory test development and validation, quality control procedures, and proficiency testing to assure their quality. In this article, we review the development and characterization of RMs for clinical molecular genetic tests. We describe various types of RMs and how to access and utilize them, especially focusing on the Genetic Testing Reference Materials Coordination Program (Get-RM) and the Genome in a Bottle (GIAB) Consortium. This review also reinforces the need for collaborative efforts in the clinical genetic testing community to develop additional RMs.

Pharmacogenetic allele nomenclature: International workgroup recommendations for test result reporting

This article provides nomenclature recommendations developed by an international workgroup to increase transparency and standardization of pharmacogenetic (PGx) result reporting. Presently, sequence variants identified by PGx tests are described using different nomenclature systems. In addition, PGx analysis may detect different sets of variants for each gene, which can affect interpretation of results. This practice has caused confusion and may thereby impede the adoption of clinical PGx testing. Standardization is critical to move PGx forward.

Characterization of 137 Genomic DNA Reference Materials for 28 Pharmacogenetic Genes: A GeT-RM Collaborative Project

Pharmacogenetic testing is increasingly available from clinical laboratories. However, only a limited number of quality control and other reference materials are currently available to support clinical testing. To address this need, the Centers for Disease Control and Prevention-based Genetic Testing Reference Material Coordination Program, in collaboration with members of the pharmacogenetic testing community and the Coriell Cell Repositories, has characterized 137 genomic DNA samples for 28 genes commonly genotyped by pharmacogenetic testing assays (CYP1A1, CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, CYP3A5, CYP4F2, DPYD, GSTM1, GSTP1, GSTT1, NAT1, NAT2, SLC15A2, SLC22A2, SLCO1B1, SLCO2B1, TPMT, UGT1A1, UGT2B7, UGT2B15, UGT2B17, and VKORC1). One hundred thirty-seven Coriell cell lines were selected based on ethnic diversity and partial genotype characterization from earlier testing. DNA samples were coded and distributed to volunteer testing laboratories for targeted genotyping using a number of commercially available and laboratory developed tests. Through consensus verification, we confirmed the presence of at least 108 variant pharmacogenetic alleles. These samples are also being characterized by other pharmacogenetic assays, including next-generation sequencing, which will be reported separately. Genotyping results were consistent among laboratories, with most differences in allele assignments attributed to assay design and variability in reported allele nomenclature, particularly for CYP2D6, UGT1A1, and VKORC1. These publicly available samples will help ensure the accuracy of pharmacogenetic testing.

Development of a genomic DNA reference material panel for Rett syndrome (MECP2-related disorders) genetic testing

Rett syndrome is a dominant X-linked disorder caused by point mutations (approximately 80%) or by deletions or insertions (approximately 15% to 18%) in the MECP2 gene. It is most common in females but lethal in males, with a distinctly different phenotype. Rett syndrome patients have severe neurological and behavioral problems. Clinical genetic testing laboratories commonly use characterized genomic DNA reference materials to assure the quality of the testing process; however, none are commercially available for MECP2 genetic testing. The Centers for Disease Control and Prevention's Genetic Testing Reference Material Coordination Program, in collaboration with the genetic testing community and the Coriell Cell Repositories, established 27 new cell lines and characterized the MECP2 mutations in these and in 8 previously available cell lines. DNA samples from the 35 cell lines were tested by eight clinical genetic testing laboratories using DNA sequence analysis and methods to assess copy number (multiplex ligation-dependent probe amplification, semiquantitative PCR, or array-based comparative genomic hybridization). The eight common point mutations known to cause approximately 60% of Rett syndrome cases were identified, as were other MECP2 variants, including deletions, duplications, and frame shift and splice-site mutations. Two of the 35 samples were from males with MECP2 duplications. These MECP2 and other characterized genomic DNA samples are publicly available from the NIGMS Repository at the Coriell Cell Repositories.

Current landscape and new paradigms of proficiency testing and external quality assessment for molecular genetics

CONTEXT

Participation in proficiency testing (PT) or external quality assessment (EQA) programs allows the assessment and comparison of test performance among different clinical laboratories and technologies. In addition to the approximately 2300 tests for individual genetic disorders, recent advances in technology have enabled the development of clinical tests that quickly and economically analyze the entire human genome. New PT/EQA approaches are needed to ensure the continued quality of these complex tests.

OBJECTIVES

To review the availability and scope of PT/EQA for molecular genetic testing for inherited conditions in Europe, Australasia, and the United States; to evaluate the successes and demonstrated value of available PT/EQA programs; and to examine the challenges to the provision of comprehensive PT/EQA posed by new laboratory practices and methodologies.

DATA SOURCES

The available literature on this topic was reviewed and supplemented with personal experiences of several PT/EQA providers.

CONCLUSIONS

Proficiency testing/EQA schemes are available for common genetic disorders tested in many clinical laboratories but are not available for most genetic tests offered by only one or a few laboratories. Provision of broad, method-based PT schemes, such as DNA sequencing, would allow assessment of many tests for which formal PT is not currently available. Participation in PT/EQA improves the quality of testing by identifying inaccuracies that laboratories can trace to errors in their testing processes. Areas of research and development to ensure that PT/EQA programs can meet the needs of new and evolving genetic tests and technologies are identified and discussed.

Molecular diagnostics: harmonization through reference materials, documentary standards and proficiency testing

There is a great need for harmonization in nucleic acid testing for infectious disease and clinical genetics. The proliferation of assay methods, the number of targets for molecular diagnostics and the absence of standard reference materials contribute to variability in test results among laboratories. This article provides a comprehensive overview of reference materials, related documentary standards and proficiency testing programs. The article explores the relationships among these resources and provides necessary information for people practicing in this area that is not taught in formal courses and frequently is obtained on an ad hoc basis. The aim of this article is to provide helpful tools for molecular diagnostic laboratories.

Development and characterization of reference materials for MTHFR, SERPINA1, RET, BRCA1, and BRCA2 genetic testing

Well-characterized reference materials (RMs) are integral in maintaining clinical laboratory quality assurance for genetic testing. These RMs can be used for quality control, monitoring of test performance, test validation, and proficiency testing of DNA-based genetic tests. To address the need for such materials, the Centers for Disease Control and Prevention established the Genetic Testing Reference Material Coordination Program (GeT-RM), which works with the genetics community to improve public availability of characterized RMs for genetic testing. To date, the GeT-RM program has coordinated the characterization of publicly available genomic DNA RMs for a number of disorders, including cystic fibrosis, Huntington disease, fragile X, and several genetic conditions with relatively high prevalence in the Ashkenazi Jewish population. Genotypic information about a number of other cell lines has been collected and is also available. The present study includes the development and commutability/genotype characterization of 10 DNA samples for clinically relevant mutations or sequence variants in the following genes: MTHFR; SERPINA1; RET; BRCA1; and BRCA2. DNA samples were analyzed by 19 clinical genetic laboratories using a variety of assays and technology platforms. Concordance was 100% for all samples, with no differences observed between laboratories using different methods. All DNA samples are available from Coriell Cell Repositories and characterization information can be found on the GeT-RM website.

Development of genomic reference materials for cystic fibrosis genetic testing

The number of different laboratories that perform genetic testing for cystic fibrosis is increasing. However, there are a limited number of quality control and other reference materials available, none of which cover all of the alleles included in commercially available reagents or platforms. The alleles in many publicly available cell lines that could serve as reference materials have neither been confirmed nor characterized. The Centers for Disease Control and Prevention-based Genetic Testing Reference Material Coordination Program, in collaboration with members of the genetic testing community as well as Coriell Cell Repositories, have characterized an extended panel of publicly available genomic DNA samples that could serve as reference materials for cystic fibrosis testing. Six cell lines [containing the following mutations: E60X (c.178G>T), 444delA (c.312delA), G178R (c.532G>C), 1812-1G>A (c.1680-1G>A), P574H (c.1721C>A), Y1092X (c.3277C>A), and M1101K (c.3302T>A)] were selected from those existing at Coriell, and seven [containing the following mutations: R75X (c.223C>T), R347H (c.1040G>A), 3876delA (c.3744delA), S549R (c.1646A>C), S549N (c.1647G>A), 3905insT (c.3773_3774insT), and I507V (c.1519A>G)] were created. The alleles in these materials were confirmed by testing in six different volunteer laboratories. These genomic DNA reference materials will be useful for quality assurance, proficiency testing, test development, and research and should help to assure the accuracy of cystic fibrosis genetic testing in the future. The reference materials described in this study are all currently available from Coriell Cell Repositories.

Consensus characterization of 16 FMR1 reference materials: a consortium study

Fragile X syndrome, which is caused by expansion of a (CGG)(n) repeat in the FMR1 gene, occurs in approximately 1:3500 males and causes mental retardation/behavioral problems. Smaller (CGG)(n) repeat expansions in FMR1, premutations, are associated with premature ovarian failure and fragile X-associated tremor/ataxia syndrome. An FMR1-sizing assay is technically challenging because of high GC content of the (CGG)(n) repeat, the size limitations of conventional PCR, and a lack of reference materials available for test development/validation and routine quality control. The Centers for Disease Control and Prevention and the Association for Molecular Pathology, together with the genetic testing community, have addressed the need for characterized fragile X mutation reference materials by developing characterized DNA samples from 16 cell lines with repeat lengths representing important phenotypic classes and diagnostic cutoffs. The alleles in these materials were characterized by consensus analysis in nine clinical laboratories. The information generated from this study is available on the Centers for Disease Control and Prevention and Coriell Cell Repositories websites. DNA purified from these cell lines is available to the genetics community through the Coriell Cell Repositories. The public availability of these reference materials should help support accurate clinical fragile X syndrome testing.

Developing a sustainable process to provide quality control materials for genetic testing

PURPOSE

To provide a summary of the outcomes of two working conferences organized by the Centers for Disease Control and Prevention (CDC), to develop recommendations for practical, sustainable mechanisms to make quality control (QC) materials available to the genetic testing community.

METHODS

Participants were selected to include experts in genetic testing and molecular diagnostics from professional organizations, government agencies, industry, laboratories, academic institutions, cell repositories, and proficiency testing (PT)/external Quality Assessment (EQA) programs. Current efforts to develop QC materials for genetic tests were reviewed; key issues and areas of need were identified; and workgroups were formed to address each area of need and to formulate recommendations and next steps.

RESULTS

Recommendations were developed toward establishing a sustainable process to improve the availability of appropriate QC materials for genetic testing, with an emphasis on molecular genetic testing as an initial step.

CONCLUSIONS

Improving the availability of appropriate QC materials is of critical importance for assuring the quality of genetic testing, enhancing performance evaluation and PT/EQA programs, and facilitating new test development. To meet the needs of the rapidly expanding capacity of genetic testing in clinical and public health settings, a comprehensive, coordinated program should be developed. A Genetic Testing Quality Control Materials Program has therefore been established by CDC in March 2005 to serve these needs.

Paralysis and killing of Caenorhabditis elegans by enteropathogenic Escherichia coli requires the bacterial tryptophanase gene

Pathogenic Escherichia coli, including enteropathogenic E. coli (EPEC), enterohaemorrhagic E. coli (EHEC), enteroinvasive E. coli (EIEC) and enterotoxigenic E. coli (ETEC) are major causes of food and water-borne disease. We have developed a genetically tractable model of pathogenic E. coli virulence based on our observation that these bacteria paralyse and kill the nematode Caenorhabditis elegans. Paralysis and killing of C. elegans by EPEC did not require direct contact, suggesting that a secreted toxin mediates the effect. Virulence against C. elegans required tryptophan and bacterial tryptophanase, the enzyme catalysing the production of indole and other molecules from tryptophan. Thus, lack of tryptophan in growth media or deletion of tryptophanase gene failed to paralyse or kill C. elegans. While known tryptophan metabolites failed to complement an EPEC tryptophanase mutant when presented extracellularly, complementation was achieved with the enzyme itself expressed either within the pathogen or within a cocultured K12 strains. Thus, an unknown metabolite of tryptophanase, derived from EPEC or from commensal non-pathogenic strains, appears to directly or indirectly regulate toxin production within EPEC. EPEC strains containing mutations in the locus of enterocyte effacement (LEE), a pathogenicity island required for virulence in humans, also displayed attenuated capacity to paralyse and kill nematodes. Furthermore, tryptophanase activity was required for full activation of the LEE1 promoter, and for efficient formation of actin-filled membranous protrusions (attaching and effacing lesions) that form on the surface of mammalian epithelial cells following attachment and which depends on LEE genes. Finally, several C. elegans genes, including hif-1 and egl-9, rendered C. elegans less susceptible to EPEC when mutated, suggesting their involvement in mediating toxin effects. Other genes including sek-1, mek-1, mev-1, pgp-1,3 and vhl-1, rendered C. elegans more susceptible to EPEC effects when mutated, suggesting their involvement in protecting the worms. Moreover we have found that C. elegans genes controlling lifespan (daf-2, age-1 and daf-16), also mediate susceptibility to EPEC. Together, these data suggest that this C. elegans/EPEC system will be valuable in elucidating novel factors relevant to human disease that regulate virulence in the pathogen or susceptibility to infection in the host.

Applying public health strategies to primary immunodeficiency diseases: a potential approach to genetic disorders

Primary immunodeficiency (PI) diseases are a group of primarily single-gene disorders of the immune system. Approximately 100 separate PI diseases have been described, but <20 probably account for >90% of cases. Although diverse, PI diseases share the common feature of susceptibility to infection and result in substantial morbidity and shortened life spans. Most important, prompt diagnosis and treatment can now lead to life-saving treatment and result in marked improvements in the quality and length of life for persons with PI diseases. In November 2001, a workshop was convened by CDC in Atlanta, Georgia, to discuss ways to improve health outcomes among persons with PI disease. A multidisciplinary panel of persons knowledgeable in PI diseases and public health met to identify and discuss public health strategies that can be applied to PI diseases and possibly for other genetic disorders. A systematic assessment based on the established public health framework was applied to the growing group of PI diseases, whose diverse genetic mutations span multiple components of the immune system but all lead to increased incidence and severity of infections. During the meeting, specialists in clinical immunology, public health, genetics, pediatrics, health communication, and ethics from state and federal agencies, academic centers, professional organizations, and advocacy foundations discussed the four components of the public health framework as they relate to PI diseases. These four components include 1) public health assessment (application of traditional public health methods to assess the occurrence and impact of PI diseases on communities); 2) population-based interventions (development, implementation, and evaluation of screening tests administered to newborns and clinical algorithms for early recognition of symptomatic persons to facilitate the earliest possible diagnosis and treatment for PI diseases); 3) evaluation of screening and diagnostic tools (to ensure their quality and appropriateness for identification of patients with PI diseases); and 4) communication (communication with and information dissemination to health-care providers and the public to facilitate prompt and appropriate diagnosis and intervention). The working group's deliberations focused on challenges and opportunities, priority research questions, and recommendations for future action for these four components. These recommendations, developed by workshop participants, will be useful to medical and public health professionals who are evaluating methods to increase recognition of PI diseases and other genetic disorders.

Role of the periplasmic domain of the Escherichia coli NarX sensor-transmitter protein in nitrate-dependent signal transduction and gene regulation

The narX, narQ and narL genes of Escherichia coli encode a nitrate-responsive two-component regulatory system that controls the expression of many anaerobic electron-transport- and fermentation-related genes. When nitrate is present, the NarX and NarQ sensor-transmitter proteins function to activate the response-regulator protein, NarL, which in turn binds to its DNA-recognition sites to modulate gene expression. The sensor-transmitter proteins are anchored in the cytoplasmic membrane by two transmembrane domains that are separated by a periplasmic region of approximately 115 amino acids. In this study we report the isolation and characterization of narX* (star) mutants that constitutively activate nitrate reductase (narGHJI) gene expression and repress fumarate reductase (frdABCD) gene expression when no nitrate is provided for the cell. An additional narX mutant was identified that has lost its ability to respond to environmental signals. Each narX defect was caused by a single amino acid substitution within a conserved 17 amino acid sequence, called the 'P-box', in the periplasmic exposed region of the NarX protein. As a result, DNA binding is then 'locked-on' or 'locked-off' to give the observed pattern of gene expression. Diploid analysis of these narX mutants showed that a NarX P-box mutant which conferred a 'locked-on' phenotype was trans dominant over wild-type NarX. Both were also trans dominant over the NarX P-box mutant which conferred a 'locked-off' phenotype. Certain narX P-box mutations, when combined with a narX 'linker' region mutation, were recessive to the NarX linker mutation. Finally, a truncated form of the NarX protein that lacked the periplasmic and membrane regions also showed a 'locked-on' phenotype in vivo. Thus, the periplasmic and membrane domains are essential for signal transduction to NarL. From these findings, we propose that nitrate is detected in the periplasmic space of the cell, and that a signal-transduction event through the cytoplasmic membrane into the interior of the cell modulates the NarX-dependent phosphorylation/dephosphorylation of NarL.

The dsg gene of Myxococcus xanthus encodes a protein similar to translation initiation factor IF3

The dsg mutants of Myxococcus xanthus are defective in fruiting body development and sporulation, yet they grow normally. The deduced amino acid sequence of the dsg gene product is 50 and 51% identical to the amino acid sequence of translation initiation factor IF3 of both Escherichia coli and Bacillus stearothermophilus, respectively. However, the Dsg protein has a carboxy-terminal extension of 66 amino acids, which are absent from its E. coli and B. stearothermophilus homologs. The Shine-Dalgarno sequence GGAGG and 5 bases further upstream are identical in M. xanthus and several enteric bacteria, despite the wide phylogenetic gap between these species. The infC gene, which encodes IF3 in enteric bacteria, starts with the atypical translation initiation codon AUU, which is known to be important for regulating the cellular level of IF3 in E. coli. Translation of the Dsg protein overexpressed from the M. xanthus dsg gene in E. coli cells initiates at an AUC codon, an atypical initiation codon in the AUU class. The dsg mutants DK429 and DK439 carry the same missense mutation that changes Gly-134 to Glu in a region of amino acid identity.

The Myxococcus xanthus dsg gene product performs functions of translation initiation factor IF3 in vivo

The amino acid sequence of the Dsg protein is 50% identical to that of translation initiation factor IF3 of Escherichia coli, the product of its infC gene. Anti-E. coli IF3 antibodies cross-react with the Dsg protein. Tn5 insertion mutations in dsg are lethal. When ample nutrients are available, however, certain dsg point mutant strains grow at the same rate as wild-type cells. Under the starvation conditions that induce fruiting body development, these dsg mutants begin to aggregate but fail to develop further. The level of Dsg antigen, as a fraction of total cell protein, does not change detectably during growth and development, as expected for a factor essential for protein synthesis. The amount of IF3 protein in E. coli is known to be autoregulated at the translational level. This autoregulation is lost in an E. coli infC362 missense mutant. The dsg+ gene from Myxococcus xanthus restores normal autoregulation to the infC362 mutant strain. Dsg is distinguished from IF3 of E. coli, other enteric bacteria, and Bacillus stearothermophilus by having a C-terminal tail of 66 amino acids. Partial and complete deletion of this tail showed that it is needed for certain vegetative and developmental functions but not for viability.

Nitrate- and molybdenum-independent signal transduction mutations in narX that alter regulation of anaerobic respiratory genes in Escherichia coli

Escherichia coli can respire anaerobically by reducing nitrate, trimethylamine-N-oxide, dimethyl sulfoxide, or fumarate. When nitrate is present, expression of the genes for fumarate (frdABCD), trimethylamine-N-oxide, and dimethyl sulfoxide (dmsABC) is repressed while expression of the nitrate reductase (narGHJI) gene is induced. This regulation requires molybdate and is mediated by the narX and narL gene products, which together form a two-component regulatory system. We provide evidence that NarX is a nitrate and molybdenum sensor which activates NarL when nitrate is available to cells. Mutants generated by hydroxylamine mutagenesis were repressed for frdA-lacZ expression even when cells were grown in the absence of nitrate. The mutations responsible for three of these nitrate independence (NarX*) phenotypes were localized to narX and further characterized in vivo for their ability to repress frdA-lacZ expression. Two of the mutants (the narX64 and narX71 mutants) had a greatly reduced requirement for molybdenum to function but still responded to nitrate. In contrast, a third mutant (the narX32 mutant) required molybdenum but did not exhibit full repression of frdA-lacZ expression even when nitrate was present. These narX* alleles also caused the induction of nitrate reductase gene expression and the repression of a dmsA-lacZ fusion in the absence of nitrate. Each narX* mutation was determined to lie in an 11-amino-acid region of the NarX polypeptide that follows a proposed transmembrane domain. We suggest that the conformation of the narX* gene products is altered such that even in the absence of nitrate each of these gene products more closely resembles the wild-type NarX protein when nitrate is present. These data establish a clear role for the narX gene product in gene regulation and strongly suggest its role in sensing nitrate and molybdenum.

Identification of a second gene involved in global regulation of fumarate reductase and other nitrate-controlled genes for anaerobic respiration in Escherichia coli

Fumarate reductase catalyzes the final step of anaerobic electron transport in Escherichia coli when fumarate is used as a terminal electron acceptor. Transcription of the fumarate reductase operon (frdABCD) was repressed when cells were grown in the presence of either of the preferred terminal electron acceptors, oxygen or nitrate, and was stimulated modestly by fumarate. We have previously identified a locus called frdR which pleiotropically affects nitrate repression of fumarate reductase, trimethylamine N-oxide reductase, and alcohol dehydrogenase gene expression and nitrate induction of nitrate reductase expression (L. V. Kalman and R. P. Gunsalus, J. Bacteriol. 170:623-629, 1988). Transformation of various frdR mutants with plasmids identified two complementation groups, indicating that the frdR locus is composed of two genes. One class of mutants was not completely restored to wild-type frdA-lacZ expression or nitrate reductase induction when complemented with multicopy narX+ plasmids, whereas low-copy narX+ plasmid-containing strains were. A second class of frdR mutants was identified and shown to correspond to a previously described gene, narL (frdR2). Complementation of these strains with multicopy narL+ plasmids resulted in superrepression of frdA-lacZ expression and moderate elevation of nitrate reductase expression. Multicopy plasmids containing both narL+ and narX+ or only narL+ were able to complement narL mutants, whereas narX+ plasmids complemented narX mutants only when present in a copy number approximately equal to that of narL. Both narL and narX mutants retained normal oxygen control of frdA-lacZ expression. Both types of mutants are pleiotropic, as evidenced by derepressed levels of the fumarate reductase and trimethylamine N-oxide reductase enzymes and by defective induction of nitrate reductase when cells were grown in the presence of nitrate. These results indicate that both the narL and narX gene products must be present in a defined ratio in the cell. We conclude that these proteins interact to effect normal nitrate control of the anaerobic electron transport-associated operons. From these studies, we propose that narX encodes a nitrate sensor protein while narL encodes a DNA-binding regulatory protein which together function in a manner analogous to other two-component regulatory systems.

Nucleotide sequence of the narL gene that is involved in global regulation of nitrate controlled respiratory genes of Escherichia coli

The DNA sequence was determined for the narL gene of Escherichia coli. This gene is involved in global regulation of a number of nitrate controlled genes including frdABCD, tor, narGHJI, and adhE which are associated with bacterial respiration and fermentation. Comparison of the deduced amino acid sequence of narL to that of other bacterial genes revealed significant homologies to the phoB, ompR, and virG gene products based on the presence of similar protein domains. These DNA binding proteins are members of two-component regulatory systems. The similarities suggest that narL may also participate in such a two-component regulatory system and that the narR gene, which lies upstream of narL, may encode a second component required for nitrate control of gene regulation. In vitro protein synthesis experiments using a narL plasmid identified a putative NarL protein of 29 kDa in size consistent with the DNA sequence analysis. Primer extension experiments revealed the presence of two 5' termini for narL mRNA, and indicates that transcription may be complex.

The frdR gene of Escherichia coli globally regulates several operons involved in anaerobic growth in response to nitrate

Fumarate reductase catalyzes the terminal step of anaerobic electron transport with fumarate as a terminal electron acceptor. Transcription of the fumarate reductase (frdABCD) operon in Escherichia coli is repressed in the presence of the preferred terminal electron acceptors, oxygen and nitrate. To identify trans-acting genes involved in regulation by nitrate, a number of E. coli mutants were generated in which expression of a frdA'-'lacZ protein fusion was no longer fully repressed by nitrate. One of these mutants, strain LK23R35, exhibited 17-fold higher beta-galactosidase activity than the wild-type strain when grown anaerobically in the presence of nitrate. When grown aerobically in the presence of nitrate, it contained three- to fourfold more beta-galactosidase activity than the wild-type strain did. Oxygen regulation of frd expression, however, was unaffected by the mutation, since the level of beta-galactosidase activity in both strains was nearly identical when they were grown in the absence of nitrate either aerobically or anaerobically. To confirm that the mutation acts in trans to frdABCD, we measured fumarate reductase levels and found them to parallel FrdA'-beta-galactosidase activity under all growth conditions tested. The effect of the mutation is pleiotropic, since the levels of nitrate reductase in LK23R35 were not induced by the addition of nitrate. The frdR mutant was also derepressed for nitrate control of the trimethylamine-N-oxide reductase and alcohol dehydrogenase enzymes. The mutation maps in a region between trp and hemA at 27 min on the E. coli chromosome. This gene, where we call frdR, is involved in both positive and negative regulation of electron transport and fermentation associated genes. A cloned 4.9-kilobase fragment of chromosomal DNA was found to complement the frdR mutation; both repression of fumarate reductase gene expression and activation of nitrate reductase gene expression were restored.