American College of Medical Genetics/American Society of Human Genetics Test and Technology Transfer Committee Working Group. Tandem mass spectrometry in newborn screening. American College of Medical Genetics/American Society of Human Genetics Test and Technology Transfer Committee Working Group

The expanding diagnostic toolbox for rare genetic diseases

Genomic technologies, such as targeted, exome and short-read genome sequencing approaches, have revolutionized the care of patients with rare genetic diseases. However, more than half of patients remain without a diagnosis. Emerging approaches from research-based settings such as long-read genome sequencing and optical genome mapping hold promise for improving the identification of disease-causal genetic variants. In addition, new omic technologies that measure the transcriptome, epigenome, proteome or metabolome are showing great potential for variant interpretation. As genetic testing options rapidly expand, the clinical community needs to be mindful of their individual strengths and limitations, as well as remaining challenges, to select the appropriate diagnostic test, correctly interpret results and drive innovation to address insufficiencies. If used effectively - through truly integrative multi-omics approaches and data sharing - the resulting large quantities of data from these established and emerging technologies will greatly improve the interpretative power of genetic and genomic diagnostics for rare diseases.

Genetic Diagnosis in a Cohort of Adult Patients with Inherited Metabolic Diseases: A Single-Center Experience

Inherited metabolic diseases (IMDs) are genetic conditions that result in metabolism alterations. Although research-based Next Generation Sequencing (NGS) testing for IMD has been recently implemented, its application in a clinical diagnostic setting remains challenging. Thus, we aimed at investigating the genetic diagnostic approach in a cohort of adult patients with IMDs referred to our adult metabolic unit. A retrospective analysis was performed collecting demographic, clinical, and genetic data of patients referred to the Adult Metabolic Unit in Padua from November 2017 to March 2022. In total, 108 adult patients (mean age: 33 years ± 17, 55% women) were enrolled in the study, and 83 (77%) of the patients transitioned from the pediatric metabolic clinics. The most prevalent groups of IMDs were disorders of complex molecule degradation (32 patients) and disorders of amino acid metabolism (31) followed by disorders of carbohydrates (26). Molecular genetic diagnosis was reported by 69 (64%) patients, with the higher rate reported by patients referred from specialty other than pediatric (88% vs. 55%). Almost all the subjects (92%) with disorders of complex molecule degradation had a genetic diagnosis. Patients with disorders of amino acid metabolism and disorders of carbohydrates had almost the same rate of genetic test (39% and 38%, respectively). Among the patients without a genetic diagnosis that we tested, two novel mutations in disease-associated genes were detected. In our single-center cohort, a consistent proportion (36%) of subjects with IMDs reaches the adulthood without a genetic demonstration of the disease. This lack, even if in some cases could be related to disease-specific diagnostic approach or to different disease onset, could be detrimental to patient management and impact to some of the specific needs of adult subjects.

Expanded Newborn Screening Program in Slovenia using Tandem Mass Spectrometry and Confirmatory Next Generation Sequencing Genetic Testing

INTRODUCTION

In the last two decades, the introduction of tandem mass spectrometry in clinical laboratories has enabled simultaneous testing of numerous acylcarnitines and amino acids from dried blood spots for detecting many aminoacidopathies, organic acidurias and fatty acid oxidation disorders. The expanded newborn screening was introduced in Slovenia in September 2018. Seventeen metabolic diseases have been added to the pre-existing screening panel for congenital hypothyroidism and phenylketonuria, and the newborn screening program was substantially reorganized and upgraded.

METHODS

Tandem mass spectrometry was used for the screening of dried blood spot samples. Next-generation sequencing was introduced for confirmatory testing. Existing heterogeneous hospital information systems were connected to the same laboratory information system to allow barcode identification of samples, creating reports, and providing information necessary for interpreting the results.

RESULTS

In t he first y ear of t he expanded newborn screening a total of 15,064 samples w ere screened. Four patients were confirmed positive with additional testing.

CONCLUSIONS

An expanded newborn screening program was successfully implemented with the first patients diagnosed before severe clinical consequences.

Targeted next generation sequencing for newborn screening of Menkes disease

PURPOSE

Population-based newborn screening (NBS) allows early detection and treatment of inherited disorders. For certain medically-actionable conditions, however, NBS is limited by the absence of reliable biochemical signatures amenable to detection by current platforms. We sought to assess the analytic validity of an ATP7A targeted next generation DNA sequencing assay as a potential newborn screen for one such disorder, Menkes disease.

METHODS

Dried blood spots from control or Menkes disease subjects (n = 22) were blindly analyzed for pathogenic variants in the copper transport gene, ATP7A. The analytical method was optimized to minimize cost and provide rapid turnaround time.

RESULTS

The algorithm correctly identified pathogenic ATP7A variants, including missense, nonsense, small insertions/deletions, and large copy number variants, in 21/22 (95.5%) of subjects, one of whom had inconclusive diagnostic sequencing previously. For one false negative that also had not been detected by commercial molecular laboratories, we identified a deep intronic variant that impaired ATP7A mRNA splicing.

CONCLUSIONS

Our results support proof-of-concept that primary DNA-based NBS would accurately detect Menkes disease, a disorder that fulfills Wilson and Jungner screening criteria and for which biochemical NBS is unavailable. Targeted next generation sequencing for NBS would enable improved Menkes disease clinical outcomes, establish a platform for early identification of other unscreened disorders, and complement current NBS by providing immediate data for molecular confirmation of numerous biochemically screened condition.

Misclassification of VLCAD carriers due to variable confirmatory testing after a positive NBS result

The Iowa Newborn Screening (NBS) Program began screening for very long-chain acyl-CoA dehydrogenase deficiency (VLCAD) in 2003. Untreated VLCAD can lead to liver failure, heart failure, and death. Current confirmatory testing recommendations by the American College of Medical Genetics (ACMG) for VLCAD list molecular and functional analysis (i.e., fibroblast fatty acid oxidation probe) as optional. This can lead to misclassification of VLCAD carriers as false positives. Iowa implemented a comprehensive VLCAD confirmatory testing algorithm at the beginning of 2016 that included both molecular and fibroblast analysis. Here, we compare the historic multi-algorithmic confirmatory testing protocol (2005-2016) to this comprehensive protocol (2016-2017). A metabolic specialist reviewed all medical records and NBS data for each out-of-range VLCAD that fell in each testing period. During the comprehensive testing period, 48,651 specimens were screened. Thirteen individuals with out-of-range C14:1 results were classified as follows after review: ten carriers, zero true positives, zero false positives, zero lost to follow-up, and four unable to assess carrier status. During the variable testing period, a total of 486,566 specimens were screened. Eighty-five individuals with out-of-range C14:1 were classified as follows: 45 carriers, two true positives, four false positives, four lost to follow-up, and 30 unable to assess carrier status. Our findings suggest that many out-of-range VLCAD cases that do not receive molecular confirmatory testing could be carriers mistakenly classified as false positives. We recommend comprehensive molecular and functional testing for all children with out-of-range VLCAD NBS results.

Metabolomics in genetic testing

Metabolomics is an intriguing field of study providing a new readout of the biochemical activities taking place at the moment of sampling within a subject's biofluid or tissue. Metabolite concentrations are influenced by several factors including disease, environment, drugs, diet and, importantly, genetics. Metabolomics signatures, which describe a subject's phenotype, are useful for disease diagnosis and prognosis, as well as for predicting and monitoring the effectiveness of treatments. Metabolomics is conventionally divided into targeted (i.e., the quantitative analysis of a predetermined group of metabolites) and untargeted studies (i.e., analysis of the complete set of small-molecule metabolites contained in a biofluid without a pre-imposed metabolites-selection). Both approaches have demonstrated high value in the investigation and understanding of several monogenic and multigenic conditions. Due to low costs per sample and relatively short analysis times, metabolomics can be a useful and robust complement to genetic sequencing.

The first pediatric case of glucagon receptor defect due to biallelic mutations in GCGR is identified by newborn screening of elevated arginine

Glucagon receptor (GCGR) defect (Mahvash disease) is an autosomal recessive hereditary pancreatic neuroendocrine tumor (PNET) syndrome that has only been reported in adults with pancreatic α cell hyperplasia and PNETs. We describe a 7-year-old girl with persistent hyperaminoacidemia, notable for elevations of glutamine (normal ammonia), alanine (normal lactate), dibasic amino acids (arginine, lysine and ornithine), threonine and serine. She initially was brought to medical attention by an elevated arginine on newborn screening (NBS) and treated for presumed arginase deficiency with a low protein diet, essential amino acids formula and an ammonia scavenger drug. This treatment normalized plasma amino acids. She had intermittent emesis and anorexia, but was intellectually normal. Arginase enzyme assay and ARG1 sequencing and deletion/duplication analysis were normal. Treatments were stopped, but similar pattern of hyperaminoacidemia recurred. She also had hypercholesterolemia type IIa, with only elevated LDL cholesterol, despite an extremely lean body habitus. Exome sequencing was initially non-diagnostic. Through a literature search, we recognized the pattern of hyperaminoacidemia was strikingly similar to that reported in the Gcgr^−/− knockout mice. Subsequently the patient was found to have an extremely elevated plasma glucagon and a novel, homozygous c.958_960del (p.Phe320del) variant in GCGR. Functional studies confirmed the pathogenicity of this variant. This case expands the clinical phenotype of GCGR defect in children and emphasizes the clinical utility of plasma amino acids in screening, diagnosis and monitoring glucagon signaling interruption. Early identification of a GCGR defect may provide an opportunity for potential beneficial treatment for an adult onset tumor predisposition disease.

•

Describe the first case of glucagon receptor defect uniquely identified by abnormal newborn screening for elevated arginine.

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Characterize the pattern of hyperaminoacidemia in GCGR defect.

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Expand the clinical spectrum of GCGR defect from adult to childhood with a unique gastrointestinal manifestation.

Sequencing Newborns: A Call for Nuanced Use of Genomic Technologies

Many scientists and doctors hope that affordable genome sequencing will lead to more personalized medical care and improve public health in ways that will benefit children, families, and society more broadly. One hope in particular is that all newborns could be sequenced at birth, thereby setting the stage for a lifetime of medical care and self-directed preventive actions tailored to each child's genome. Indeed, commentators often suggest that universal genome sequencing is inevitable. Such optimism can come with the presumption that discussing the potential limits, cost, and downsides of widespread application of genomic technologies is pointless, excessively pessimistic, or overly cautious. We disagree. Given the pragmatic challenges associated with determining what sequencing data mean for the health of individuals, the economic costs associated with interpreting and acting on such data, and the psychosocial costs of predicting one's own or one's child's future life plans based on uncertain testing results, we think this hope and optimism deserve to be tempered. In the analysis that follows, we distinguish between two reasons for using sequencing: to diagnose individual infants who have been identified as sick and to screen populations of infants who appear to be healthy. We also distinguish among three contexts in which sequencing for either diagnosis or screening could be deployed: in clinical medicine, in public health programs, and as a direct-to-consumer service. Each of these contexts comes with different professional norms, policy considerations, and public expectations. Finally, we distinguish between two main types of genome sequencing: targeted sequencing, where only specific genes are sequenced or analyzed, and whole-exome or whole-genome sequencing, where all the DNA or all the coding segments of all genes are sequenced and analyzed. In a symptomatic newborn, targeted or genome-wide sequencing can help guide other tests for diagnosis or for specific treatment that is urgently needed. Clinicians use the infant's symptoms (or phenotype) to interrogate the sequencing data. These same complexities and uncertainties, however, limit the usefulness of genome-wide sequencing as a population screening tool. While we recognize considerable benefit in using targeted sequencing to screen for or detect specific conditions that meet the criteria for inclusion in newborn screening panels, use of genome-wide sequencing as a sole screening tool for newborns is at best premature. We conclude that sequencing technology can be beneficially used in newborns when that use is nuanced and attentive to context.

Newborn Screening: What Does the Emergency Physician Need to Know?

Newborn screening programs were established in the United States in the early 1960s. Newborn screening programs were then developed by states and have continued to be the responsibility of the state. All states require a newborn screening, but what is required of these programs and screening panels has differed greatly by state. Historically, the most commonly screened disorders are the following: congenital hypothyroidism, congenital adrenal hyperplasia, sickle cell disease and associated hemoglobinopathies, biotinidase deficiency, galactosemia, cystic fibrosis and phenylketonuria, maple syrup urine disease, and homocystinuria. However, under new guidelines in 2006 and with new advances in technology, the scope of newborn screening programs has expanded to include at a minimum 9 organic acidurias, 5 fatty acid oxidation disorders, 3 hemoglobinopathies, and 6 other conditions. This CME article reviews the logistics of newborn screening and explores the effect of new technology and recent policy on state screens and what that means for providers. This article also highlights several of the disorders most relevant to emergency room physicians and discusses future considerations of newborn screening.

Genetic Counseling and Screening of Consanguineous Couples and Their Offspring: Recommendations of the National Society of Genetic Counselors

The objective of this document is to provide recommendations for genetic counseling and screening for consanguineous couples (related as second cousins or closer) and their offspring with the goals of1. providing preconception reproductive options2. improving pregnancy outcome and identifying reproductive choices3. reducing morbidity and mortality in the 1st years of life, and4. respecting psychosocial and multicultural issues.The recommendations are the opinions of a multicenter working group (the Consanguinity Working Group (CWG)) with expertise in genetic counseling, medical genetics, biochemical genetics, genetic epidemiology, pediatrics, perinatology, and public health genetics, which was convened by the National Society of Genetic Counselors (NSGC). The consensus of the CWG and NSGC reviewers is that beyond a thorough medical family history with follow-up of significant findings, no additional preconception screening is recommended for consanguineous couples. Consanguineous couples should be offered similar genetic screening as suggested for any couple of their ethnic group. During pregnancy, consanguineous couples should be offered maternal-fetal serum marker screening and high-resolution fetal ultrasonography. Newborns should be screened for impaired hearing and detection of treatable inborn errors of metabolism. These recommendations should not be construed as dictating an exclusive course of management, nor does use of such recommendations guarantee a particular outcome. The professional judgment of a health care provider, familiar with the facts and circumstances of a specific case, will always supersede these recommendations.

Risk of sudden death and acute life-threatening events in patients with glutaric acidemia type II

Glutaric acidemia type II (GAII) is an inborn error of metabolism caused by defects in electron transport flavoprotein (ETF) or ETF-ubiquinone oxidoreductase (ETF-QO) and typically presents with hypo- or nonketotic hypoglycemia and metabolic acidosis. The most severe forms present in early infancy and are associated with a high mortality rate. The disorder can now be detected by expanded newborn screening using tandem mass spectrometry (MS/MS), providing the opportunity for diagnosis and treatment in asymptomatic infants. We report here three infants who, despite diagnosis and treatment in the neonatal period, experienced either unexpected sudden death or an acute life-threatening event (ALTE) during the first year of life. The possible etiologies of these events and the potential impact of expanded newborn screening on the long-term outcome of GAII are discussed.

Assessment of liquid microbead arrays for the screening of newborns for spinal muscular atrophy

BACKGROUND

Spinal muscular atrophy is a common neurodegenerative disorder that has recently been considered for inclusion in the next generation of newborn screening regimens. We sought to validate liquid microbead arrays for the identification of affected individuals by direct DNA analysis.

METHODS

Assays were created to detect the homozygous deletions in exon 7 of the SMN1 gene found in approximately 95% of affected individuals by use of 2 different microbead chemistries on the Luminex 200: MultiCode-PLx and Tag-It. A series of 367 blood spots including 164 from affected individuals, 46 from known carriers, and 157 from unaffected individuals were then analyzed with each assay.

RESULTS

The MultiCode-PLx assay required 4.2 h to perform and provided correct identification of all 164 samples from affected individuals. Correct exclusion was also made for all 46 carrier and 157 unaffected individual samples. The Tag-It assay required 6.8 h, detected all samples from affected individuals, and excluded all but 1 (99.5%) of the samples from carriers and unaffected individuals. Neither method was sensitive to increasing copy numbers of the SMN2 gene.

CONCLUSIONS

Both methods showed high sensitivity and specificity for the detection of patients with spinal muscular atrophy. For both methods, ample DNA was extracted from all blood spots for analysis, and SMN2 copy numbers did not interfere. Liquid bead arrays represent a robust method for DNA analysis in newborn screening laboratories.

Policy issues related to expanded newborn screening: a review of three genetic/metabolic disorders

In 2005, a federal advisory committee recommended that the number of disorders in state newborn screening programs be expanded from 9 to 29. In view of this recommendation, state leaders will need to make cogent decisions regarding the expanse of their state newborn screening programs. They must consider several factors, including the costs and outcomes of the screening program. The expense of the initial screening test can be misleading because it does not include the cost of the entire program (testing, tracking, notifying, retesting, confirmatory testing, and follow-up). Also, outcomes such as false positive findings can be costly to newborn screening programs, result in additional testing for infants, and lead to parental concern and worry. This article examines some of the policy issues related to newborn screening and specifically focuses on three disorders recommended for newborn screening, cystic fibrosis (CF), medium-chain acyl CoA dehydrogenase Deficiency (MCADD), and beta-ketothiolase (BKT).

Rapid determination of short chain carnitines in human plasma by electrospray ionisation-ion trap mass spectrometry using capillary electrophoresis instrument as sampler

A capillary electrophoresis apparatus was used as sampler for flow injection analysis (FIA) in tandem mass spectrometry of L-carnitine and its acetyl- and propionyl-metabolites in human plasma. The capillary electrophoresis instrument was coupled to the ion trap mass spectrometer by an electrospray ionization coaxial sheath liquid interface. The electrophoresis capillary introduced the sample directly into the source by applying a prolonged sample injection. The use of the capillary electrophoresis apparatus miniaturised the FIA procedure, substantially reducing the quantities of solvents and samples used, and allowed rapid automated sequential analyses. The method was optimised and validated using a dialyzed human plasma matrix. The plasma samples were analysed after a simple, rapid deproteinisation procedure with acetonitrile and diluted 70 times before direct injection into the mass spectrometer for product ion scan MS/MS analysis in positive ionisation. The total analysis time was 5 min, including capillary preconditioning and acquisition time (3 min). The method was sensitive, allowing the determination of L-, L-acetyl- and L-propionyl-carnitines at 140, 14 and 3.6 nM concentrations (injected values) corresponding to lower limit of quantitation values in plasma of 10, 1 and 0.25 microM, respectively. The method was processed for full validation and applied to the analysis of L-carnitine and its short chain derivatives in human plasma samples.

The cost-effectiveness of expanding newborn screening for up to 21 inherited metabolic disorders using tandem mass spectrometry: results from a decision-analytic model

OBJECTIVES

In 2005, in Ontario, Canada, newborns were only screened for phenylketonuria (PKU) and hypothyroidism. Tandem mass spectrometry (MS/MS) has since been implemented as a new screening technology because it can screen for PKU and many other diseases simultaneously. We estimated the cost-effectiveness of using this technology to expand the Ontario newborn screening program to screen for each disease independently and for hypothetical bundles of up to 21 metabolic diseases.

METHODS

We constructed a decision-analytic model to estimate the incremental costs and life-years of survival that can be gained by screening or changing screening technologies. Costs and health benefits were estimated for a cohort of babies born in Ontario in 1 year. Secondary sources and expert opinion were used to estimate the test characteristics, disease prevalence, treatment effectiveness, disease progression rates, and mortality. The London Health Sciences Centre Case Costing Initiative, the Ontario Health Insurance Plan Schedule, and the Ontario Drug Benefits plan formulary were used to estimate costs.

RESULTS

Changing screening technologies, from the Guthrie test to MS/MS, for PKU detection had an incremental cost of $5,500,000 per life-year (LY) gained. We identified no diseases for which the incremental cost of screening for just that disease was less than $100,000 per LY gained. The incremental costs of screening ranged from $222,000 (HMG-CoA lyase deficiency) to $142,500,000 (glutaric acidemia type II) per LY gained. Screening for a bundle of diseases including PKU and the 14 most cost-effective diseases to screen for cost less than $70,000 per LY gained, and the incremental cost-effectiveness of adding each of the 14 diseases to the bundle was less than $100,000 per LY gained. The incremental cost of adding the 15th most cost-effective disease was $309,400 per LY gained.

CONCLUSIONS

Early diagnosis and treatment of metabolic disease is important to reduce disease severity and delay or prevent the onset of the disease. Screening at birth reduces the morbidity, mortality, and social burden associated with the irreversible effects of disease on the population. Our analysis suggests that the cost-efficiencies gained by using MS/MS to screen for bundles of diseases rather than just one disease are sufficient to warrant consideration of an expanded screening program. It is, however, not cost-effective to screen for all diseases that can be screened for using this technology.

Navigating the Maze of Newborn Screening

Newborn screening tests are obtained for all live births in the United States in an effort to identify newborns affected with, or at risk for, various genetic and metabolic diseases. This screening began in the early 1960s with an inexpensive screening test for phenylketonuria (PKU), but the introduction of new technology in the 1990s using tandem mass spectrometry provided the means to screen for over 30 additional metabolic disorders. Newborn-screening programs are state funded and operated, and many factors affect whether certain conditions are included in a state's screening program, including how severe the condition would be if left untreated, the prevalence of that condition in the state's population, and whether there is a treatment available that would improve the course of illness. Numerous ethical issues must be considered concerning newborn screening. Some of these are disparity in access to screening and care, cost of screening, lack of standardized protocols for informed consent, and inconsistent policies for not only abnormal laboratory values but also follow-up diagnosis and medical management. Nurses who work with mothers and infants need to (1) be aware of the laws and policies regarding newborn screening for their state, (2) become familiar with the conditions screened, their inheritance patterns, and their early symptoms, and (3) understand what parents need to be told so that they are able to make informed decisions about their newborns.

Newborn blood spot screening and genetic services: a survey of Minnesota primary care physicians

PURPOSE

To (1) obtain guidance on the preferred content and format of quick reference newborn blood spot screening information from the Minnesota Department of Health; (2) determine primary care physicians' perceptions of the benefits of genetic services; and (3) determine primary care physicians' satisfaction with genetic counseling services.

METHODS

A written survey was mailed to family physicians and pediatricians in Minnesota (n = 300).

RESULTS

Eighty physicians responded (28% response rate). Whereas 70% of respondents felt previous information received from the newborn screening program was adequate, 83% were interested in quick reference information. The majority of physicians preferred this information as a laminated sheet (63%). Physician procedure for an abnormal screen, newborn screening program protocol for an abnormal screen, and disease treatment and follow-up information were recommended for inclusion on quick reference. Over half of physicians agreed with the following benefits of genetic services: provide testing options (88%); evaluate family members (88%); reduce parental anxiety (87%); provide resources (83%); provide diagnostic information (76%); determine medical needs (67%); and determine emotional needs (51%). Ninety-nine percent of physicians were satisfied with genetic counseling services.

CONCLUSIONS

Physicians indicated that reference material for primary care physicians should include a quick reference card with specific categories of information. Newborn screening programs should attempt to increase physician awareness of genetic services, including the subsequent medical and psychosocial benefits for their patients.

Biomarker Discovery, Disease Classification, and Similarity Query Processing on High-Throughput MS/MS Data of Inborn Errors of Metabolism

In newborn errors of metabolism, biomarkers are urgently needed for disease screening, diagnosis, and monitoring of therapeutic interventions. This article describes a 2-step approach to discovermetabolic markers, which involves (1) the identification ofmarker candidates and (2) the prioritization of thembased on expert knowledge of diseasemetabolism. For step 1, the authors developed a new algorithm, the biomarker identifier (BMI), to identifymarkers fromquantified diseased versus normal tandemmass spectrometry data sets. BMI produces a ranked list ofmarker candidates and discards irrelevant metabolites based on a quality measure, taking into account the discriminatory performance, discriminatory space, and variance ofmetabolites’ concentrations at the state of disease. To determine the ability of identified markers to classify subjects, the authors compared the discriminatory performance of several machine-learning paradigms and described a retrieval technique that searches and classifies abnormal metabolic profiles from a screening database. Seven inborn errors of metabolism— phenylketonuria (PKU), glutaric acidemia type I (GA-I), 3-methylcrotonylglycinemia deficiency (3-MCCD), methylmalonic acidemia (MMA), propionic acidemia (PA), medium-chain acylCoAdehydrogenase deficiency (MCADD), and 3-OH longchain acyl CoA dehydrogenase deficiency (LCHADD)—were investigated. All primarily prioritized marker candidates could be confirmed by literature. Somenovel secondary candidateswere identified (i.e., C16:1 andC4DCfor PKU, C4DCfor GA-I, and C18:1 forMCADD), which require further validation to confirmtheir biochemical role during health and disease.

Rapid measurement of plasma acylcarnitines by liquid chromatography–tandem mass spectrometry without derivatization

BACKGROUND

Tandem mass spectrometry (MS/MS) is being increasingly used to identify and measure acylcarnitines in blood and urine of children suspected of having fatty oxidation disorders and other inborn errors of metabolism. Rapid MS/MS analysis requires simple and efficient sample preparation. We developed a LC-MS/MS method for the online extraction of acylcarnitines in plasma without derivatization that requires only precipitation of proteins by acetonitrile followed by centrifugation, thus increasing efficiency.

METHODS

An API-3000 tandem mass spectrometer (SCIEX, Toronto, Canada) equipped with electrospray ionization (ESI), TurboIon Spray source, three Shimadzu LC10AD micropumps and autosampler (Shimadzu Scientific Instruments, Columbia, MD) was used to perform the analysis. Within-day and between-day imprecision was evaluated for 10 analytes in the MRM mode using 3 levels of controls. Accuracy was determined by comparing the method with another MS/MS procedure and by recovery experiments. Sensitivity and specificity were evaluated by identifying patient samples under a wide variety of clinical conditions.

RESULTS

Within-day CVs was <10% for all analytes tested and between-day CVs ranged from 4.4% to 14.2%. The method was linear in the range between 1.0 and 100 micromol/l for C2 and 0.1 and 10 micromol/l for the other acylcarnitines. The results of the comparison study yielded r values ranging between 0.948 and 0.999. Recovery ranged from 84% to 112%. The method correctly identified patients with a variety of fatty acid oxidation disorders and organic acidemias.

CONCLUSIONS

Our method is a simple procedure for the analysis of acylcarnitines in plasma with minimal sample preparation. It is thus ideal in a routine clinical setting where efficient processing of clinical samples is necessary to reduce turnaround time under conditions of high-throughput.

Modelling of classification rules on metabolic patterns including machine learning and expert knowledge

Machine learning has a great potential to mine potential markers from high-dimensional metabolic data without any a priori knowledge. Exemplarily, we investigated metabolic patterns of three severe metabolic disorders, PAHD, MCADD, and 3-MCCD, on which we constructed classification models for disease screening and diagnosis using a decision tree paradigm and logistic regression analysis (LRA). For the LRA model-building process we assessed the relevance of established diagnostic flags, which have been developed from the biochemical knowledge of newborn metabolism, and compared the models' error rates with those of the decision tree classifier. Both approaches yielded comparable classification accuracy in terms of sensitivity (>95.2%), while the LRA models built on flags showed significantly enhanced specificity. The number of false positive cases did not exceed 0.001%.

Policy issues for expanding newborn screening programs: the cystic fibrosis newborn screening experience in the United States

OBJECTIVE

To describe the screening approaches and implementation strategies for cystic fibrosis newborn screening in the 12 programs that were offered in 11 states in 2002.

STUDY DESIGN

Telephone interviews conducted in the spring of 2003 with program representatives in the 11 states. Screening approaches were defined in four overlapping categories: state mandated screening, state-wide offering, hospital based screening, and screening with informed consent.

RESULTS

Screening was state mandated in seven states but was routinely offered to most infants in nine states. The primary care provider or hospital determined if screening was done in three states (four programs). Informed consent was explicitly documented in two states. In five programs, immunoreactive trypsinogen exclusively was used to identify at-risk infants. In seven programs, a second tier DNA test was also used, but these programs each had distinct strategies. In only two programs where DNA testing was performed and normal sweat tests indicated carrier status, were results routinely provided to parents "in person" at a CF center.

CONCLUSION

The diversity of approaches for screening approaches and strategies has advantages for future policy decisions, provided that data about the clinical and psychosocial impact of screening from these programs are collected and disseminated. As additional states determine that the resources are available, programs can be designed with a more favorable benefit/risk balance as a result of the successes and challenges faced by other states.

Should children and adolescents undergo genetic testing?

Genetic testing comes in many shapes and sizes. The decision to undergo genetic testing must involve consideration of the medical, psychosocial, and reproductive benefits and risks of testing. The evaluation of risks and benefits varies significantly both between and within families. Pediatricians should keep up with the rapid advances in genetic medicine and the myriad of tests that are being developed and marketed. They also need to be familiar with the psychosocial risks and benefits that these new tests generate for individuals, families and communities. In some situations, genetic testing is merely another diagnostic tool; in other situations, genetic testing offers information about the risks for future diseases. Pediatricians need to be knowledgeable about tests that are indicated clinically and their potential psychosocial implications to best serve children, adolescents, and their families.

Genetic counseling throughout the life cycle

As the definition of genetic counseling continues to evolve, so does the application of genetic counseling services in all areas of medicine and throughout the human life cycle. While governmental policy, economics, ethics, and religion continue to influence society's views regarding the necessity of testing germ cells for mutations to prevent the birth of an affected child or predicting whether healthy adults will develop future life-threatening illness, patient autonomy in the choice of whether to know, or not know, one's genetic make-up remains a core principle of genetic counseling.

Postmortem screening for fatty acid oxidation disorders by analysis of Guthrie cards with tandem mass spectrometry in sudden unexpected death in infancy

A protocol was developed for the detection of fatty acid oxidation disorders (FOD) in cases of sudden unexpected death in infancy (SUDI). Tandem mass spectrometry blood acylcarnitine analysis of Guthrie card blood spots was performed. In the first 5 years, 1.2% of Oregon's 247 SUDI cases were identified with FOD, 2 with medium-chain acyl-CoA dehydrogenase deficiency, and one with very long-chain acyl-CoA dehydrogenase deficiency.

Cost-benefit analysis of universal tandem mass spectrometry for newborn screening

OBJECTIVE

To estimate potential costs and benefits of routinely using tandem mass spectrometry (MS/MS) to screen newborns for inborn errors of metabolism.

METHOD

Analysis of costs and benefits resulting from use of MS/MS in screening of 32 000 newborn infants using data from the Kaiser Permanente Medical Care Program of Northern California plus other published data.

SETTING

A large health maintenance organization.

RESULTS

In the base scenario, the cost per quality-adjusted life year saved by MS/MS screening was $5827; in the least favorable scenario, this cost was $11 419, and in the most favorable scenario, $736.

CONCLUSION

Costs per quality-adjusted life year saved by MS/MS screening for inborn errors of metabolism compare favorably with other mass screening programs, including those for breast and prostate cancer.

Newborn screening, informed consent, and future use of archived tissue samples

Recent advances in genetic technologies have combined with established protocols for genetic screening to provide immense benefits to individuals and the public. In most American jurisdictions, newborn screening is mandated by law and does not require parental consent for the collection or testing of the blood samples. Screening programs have been successful in identifying affected infants at an early stage for effective treatment of some genetic diseases. The public health benefit of screening programs is recognized and affirmed. However, collections of surplus, stored samples have become immensely attractive to researchers in medical genetics and the biomedical sciences. As geneticists have sought access to the newborn screening samples, they have recognized concerns related to whether they should use the samples, and, if so, under what conditions. This paper addresses the ethical issues associated with genetic screening and recommends an informed consent protocol that may be used to balance individual and parental rights with the interests of researchers who wish to use surplus samples in studies of genetic disease.

Diagnosis of very long chain acyl-dehydrogenase deficiency from an infant's newborn screening card

Very long chain fatty acid dehydrogenase (VLCAD) deficiency is a rare but treatable cause of cardiomyopathy, fatty liver, skeletal myopathy, pericardial effusions, ventricular arrhythmias, and sudden death. Unrecognized, VLCAD deficiency may be rapidly progressive and fatal, secondary to its cardiac involvement. Because early diagnosis improves outcome, we present a neonate with VLCAD deficiency in whom retrospective analysis of the newborn screening card revealed that a correct diagnosis could have been made by newborn screening using tandem mass spectrometry. Our patient demonstrated a classic neonatal course with transient hypoglycemia at birth, interpreted as culture-negative sepsis, followed by a quiescent period notable only for hypotonia and poor feeding. At 3 months, he presented with cardiorespiratory failure and pericardial effusions, requiring pericardiocentesis, tracheostomy, and prolonged mechanical ventilation. Plasma free-fatty acid and acylcarnitine profiles demonstrated small but significant elevations of C14:2, C14:1, C16, and C18:1 acylcarnitine species, findings consistent with a biochemical diagnosis of VLCAD deficiency. Enteral feeds were changed to Portagen formula with marked improvement in cardiac symptoms over several weeks. To confirm the biochemical diagnosis, molecular analysis was performed by analysis of genomic DNA on a blood sample of the patient. Sequencing analysis and delineation of VLCAD mutations were performed using polymerase chain reaction and genomic sequencing. The patient was heterozygous for 2 different disease-causing mutations at the VLCAD locus. The maternal mutation was a deletion of bp 842-3 in exon 8, causing a shift in the reading frame. The paternal mutation was G+1A in the consensus donor splice site after exon 1; this splice-site mutation would likely result in decreased mRNA. The likely consequence of these mutations is essentially a null phenotype. To determine whether this case could have been picked up by tandem mass spectrometry analysis at birth when the patient was asymptomatic, acylcarnitine analysis was performed on the patient's original newborn card (after obtaining parental consent, the original specimen was provided courtesy of Dr Kenneth Pass, Director, New York State Newborn Screening Program). The blood sample had been obtained at 1 week of age and stored at room temperature for 6 months and at 70 degrees C thereafter for 18 months. Electrospray tandem mass spectrometry used a LC-MS/MS API 2000 operated in ion evaporation mode with the TurboIonSpray ionization probe source. The acylcarnitine profile obtained from the patient's original newborn card was analyzed 2 years after it was obtained. In comparison with a normal control, there was a significant accumulation of long chain acylcarnitine species, with a prominent peak of tetradecenoylcarnitine (C14:1), the most characteristic metabolic marker of VLCAD deficiency. This profile would have likely been even more significant if it had been analyzed at the time of collection, yet 2 years later is sufficient to provide strong biochemical evidence of the underlying disorder. Discussion. VLCAD was first discovered in 1992, and clinical experience with VLCAD deficiency has been accumulating rapidly. Indeed, the patients originally diagnosed with long chain acyl-CoA deficiency suffer instead from VLCAD deficiency. The phenotype of VLCAD deficiency is heterogeneous, ranging from catastrophic metabolic and cardiac failure in infancy to mild hypoketotic, hypoglycemia, and exertional rhabdomyolysis in adults. This case demonstrates that VLCAD deficiency could have been detected from the patient's own neonatal heel-stick sample. Most likely, a presymptomatic diagnosis would have avoided at least part of a lengthy and intensive prediagnosis hospitalization that had an estimated cost of $400 000. Although VLCAD is relatively rare, timely and correct diagnosis leads to dramatic recovery, so that detection by newborn screening could prevent the onset of arrhythmias, heart failure, metabolic insufficiency, and death. Fatty acid oxidation defects, including VLCAD deficiency, may account for as many as 5% of sudden infant death patients. Recent instrumentation advances have made automated tandem mass spectrometry of routine neonatal heel-stick samples technically feasible. Pilot studies have demonstrated an incidence of fatty acid oxidation defects, including short chain, medium chain, and very long chain acyl-CoA dehydrogenase deficiencies, of approximately 1/12 000. As a result, cost-benefit ratios for this approach should be systematically examined.

Disorders of fatty acid transport and mitochondrial oxidation: challenges and dilemmas of metabolic evaluation

Inborn errors of fatty acid transport and mitochondrial oxidation (FATMO) have drawn considerable attention in recent years for the rapid pace of discovery of new defects and an ever-increasing spectrum of clinical phenotypes. Several of these disorders are not detected by conventional biochemical investigations, even when a patient is symptomatic with fasting intolerance or functional failure of fatty acid dependent tissue(s). In our view, today's major challenges are the inclusion of FATMO disorders in newborn screening programs and the investigation of the role played by individual disorders in maternal complications of pregnancy, sudden and unexpected death in early life, and pediatric acute/fulminant liver failure. Dilemmas are found in the debate over the limitations, if any, to be imposed on the expansion of newborn screening using tandem mass spectrometry, in the provision of prenatal diagnosis for otherwise treatable disorders, and in the diagnostic workup of "unclassified" cases.