Screening for medium chain acyl-CoA dehydrogenase deficiency using electrospray ionisation tandem mass spectrometry

Measurement of free carnitine and acylcarnitines in plasma by HILIC-ESI-MS/MS without derivatization

Measurement of carnitine and acylcarnitines in plasma is important in diagnosis of fatty acid β-oxidation disorders and organic acidemia. The usual method uses flow injection tandem mass spectrometry (FIA-MS/MS), which has limitations. A rapid and more accurate method was developed to be used for high-risk screening and diagnosis. Carnitine and acylcarnitines were separated by hydrophilic interaction liquid chromatography (HILIC) without derivatization and detected with a QTRAP MS/MS System. Total analysis time was 9.0min. The imprecision of within- and between-run were less than 6% and 17%, respectively. Recoveries were in the range of 85-110% at three concentrations. Some acylcarnitine isomers could be separated, such as dicarboxylic and hydroxyl acylcarnitines. The method could also separate interferent to avoid false positive results. 216 normal samples and 116 patient samples were detected with the validated method, and 49 patients were identified with fatty acid oxidation disorders or organic acidemias.

Maternal medium-chain acyl-CoA dehydrogenase deficiency identified by newborn screening

Prior to the advent of expanded newborn screening, sudden and unexplained death was often the first and only symptom of medium-chain acyl-CoA dehydrogenase deficiency (MCADD). With the use of tandem mass spectrometry, infants can now be identified and treated before a life threatening metabolic decompensation occurs. Newborn screening has also been shown to detect previously undiagnosed maternal inborn errors of metabolism. We have now diagnosed two women with MCADD following the identification of low free carnitine in their newborns. While one of the women reported prior symptoms of fasting intolerance, neither had a history of metabolic decompensation or other symptoms consistent with a fatty acid oxidation disorder. These cases illustrate the importance of including urine organic acid analysis and an acylcarnitine profile as part of the confirmatory testing algorithm for mothers when low free carnitine is identified in their infants.

Data mining methods for classification of Medium-Chain Acyl-CoA dehydrogenase deficiency (MCADD) using non-derivatized tandem MS neonatal screening data

Newborn screening programs for severe metabolic disorders using tandem mass spectrometry are widely used. Medium-Chain Acyl-CoA dehydrogenase deficiency (MCADD) is the most prevalent mitochondrial fatty acid oxidation defect (1:15,000 newborns) and it has been proven that early detection of this metabolic disease decreases mortality and improves the outcome. In previous studies, data mining methods on derivatized tandem MS datasets have shown high classification accuracies. However, no machine learning methods currently have been applied to datasets based on non-derivatized screening methods. A dataset with 44,159 blood samples was collected using a non-derivatized screening method as part of a systematic newborn screening by the PCMA screening center (Belgium). Twelve MCADD cases were present in this partially MCADD-enriched dataset. We extended three data mining methods, namely C4.5 decision trees, logistic regression and ridge logistic regression, with a parameter and threshold optimization method and evaluated their applicability as a diagnostic support tool. Within a stratified cross-validation setting, a grid search was performed for each model for a wide range of model parameters, included variables and classification thresholds. The best performing model used ridge logistic regression and achieved a sensitivity of 100%, a specificity of 99.987% and a positive predictive value of 32% (recalibrated for a real population), obtained in a stratified cross-validation setting. These results were further validated on an independent test set. Using a method that combines ridge logistic regression with variable selection and threshold optimization, a significantly improved performance was achieved compared to the current state-of-the-art for derivatized data, while retaining more interpretability and requiring less variables. The results indicate the potential value of data mining methods as a diagnostic support tool.

Dissection of biochemical borderline phenotypes in carriers and genetic variants of medium-chain acyl-CoA dehyrogenase deficiency: implications for newborn screening [corrected]

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) represents a potentially fatal fatty acid beta-oxidation disorder. Newborn screening (NBS) by tandem mass spectrometry (MS/MS) has been implemented worldwide, but is associated with unresolved questions regarding population heterogeneity, burden on healthy carriers, cut-off policies, false-positive and negative rates. In a retrospective case-control study, 333 NBS samples showing borderline acylcarnitine patterns but not reaching recall criteria were genotyped for the two most common mutations (c.985A>G/c.199C>T) and compared with genotypes and acylcarnitines of 333 controls, 68 false-positives, and 34 patients. c.985A>G was more frequently identified in the study group and false-positives compared to controls (1:4.3/1:2.3 vs. 1:42), whereas c.199C>T was found more frequently only within the false-positives (1:23). Biochemical criteria were devised to differentiate homozygous (c.985A>G), compound heterozygous (c.985A>G/c.199C>T), and heterozygous individuals. Four false-negatives were identified because our initial algorithm required an elevation of octanoylcarnitine (C(8)) and three secondary markers in the initial and follow-up sample. The new approach allowed a reduction of false-positives (by defining high cut-offs: 1.4 micromol/l for C(8); 7 for C(8)/C(12)) and false-negatives (by sequencing the ACADM gene of few suspicious samples). Our validation strategy is able to differentiate healthy carriers from patients doubling the positive predictive value (42-->88%) and to target NBS to MCADD-subsets with potentially higher risk of adverse outcome. It remains controversial, if NBS programs should aim at identifying all subsets of all diseases included. Because the natural course of milder variants cannot be assessed by observational studies, our strategy could serve as a general model for evaluation of MS/MS-based NBS.

Ethnicity of children with homozygous c.985A>G medium-chain acyl-CoA dehydrogenase deficiency: findings from screening approximately 1.1 million newborn infants

OBJECTIVES

It has been suggested that homozygous c.985A>G medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is a disease of White ethnic origin but little is known regarding its ethnic distribution. We estimated ethnic-specific homozygous c.985A>G MCADD birth prevalence from a large-scale UK newborn screening study.

METHODS

Homozygous c.985A>G MCADD cases were ascertained in six English newborn screening centres between 1 March 2004 and 28 February 2007 by screening approximately 1.1 million newborns using tandem mass spectrometry analysis of underivatised blood spot samples to quantitate octanoylcarnitine (C8). Follow-up biochemistry and mutation analyses for cases (mean triplicate C8 value >/=0.5 micromol/L) were reviewed to confirm diagnosis. Ethnicity was ascertained from clinician report and denominators from 2001 UK Census estimates of ethnic group of children less than one year.

RESULTS

Sixty-four infants were c.985A>G MCADD homozygotes (overall prevalence 5.8 per 100,000 live births; 95% CI 4.4-7.2). Sixty (93%) were White, two (3%) were mixed/other and two were of unknown ethnic origin. No Asian or Black homozygotes were identified. Proportions of White, mixed/other, Asian and Black births in screening regions were estimated, yielding homozygous c.985A>G MCADD birth prevalence of 6.9 per 100,000 (95% CI 5.2-8.8) in White, and 95% CI estimates of 0-2.7 per 100,000 in Asian and 0-5.8 in Black populations. The c.985A>G carrier frequency in the White group was estimated at one in 65 (95% CI 1/74, 1/61) under Hardy-Weinberg conditions.

CONCLUSION

c.985A>G homozygous MCADD is not found in Black and Asian ethnic groups that have been screened at birth in England. This is consistent with the earlier published observations suggesting that MCADD due to the c.985A>G mutation is a disease of White ethnic origin.

Cost-effectiveness of neonatal screening for medium chain acyl-CoA dehydrogenase deficiency: the homogeneous population of The Netherlands

OBJECTIVE

To assess the cost-effectiveness of neonatal screening on medium chain acyl-CoA dehydrogenase (MCAD) deficiency in a homogeneous population.

STUDY DESIGN

For the scenario without neonatal screening, medical chart review and interviews were performed with physicians and families of 116 Dutch patients born between 1985 and July 2003 with clinically ascertained MCAD deficiency. For the scenario with neonatal screening, 66,205 unaffected and 11 affected newborns identified by prospective neonatal screening for MCAD deficiency in the northern part of the Netherlands were evaluated. The incremental cost-effectiveness ratio (ICER) used life years (LYs) as the outcome measure by combining both scenarios in a decision model with second-order Monte Carlo simulation.

RESULTS

For the scenarios with and without neonatal screening for MCAD deficiency, costs were $6.10 and $4.22 per newborn, respectively. The main cost categories were institutionalization (64%), admissions (17%), special education (8%), laboratory testing (4%), and (para)medical contact (4%). The resulting ICER was $1653 per LY gained. Sensitivity analysis generated an ICER between $14,839 and $4345 per LY gained.

CONCLUSIONS

Screening for MCAD deficiency in a well-defined population generates an ICER well within accepted boundaries for cost-effective interventions, even after sensitivity analysis.

Feature construction can improve diagnostic criteria for high-dimensional metabolic data in newborn screening for medium-chain acyl-CoA dehydrogenase deficiency

BACKGROUND

In newborn screening with tandem mass spectrometry, multiple intermediary metabolites are quantified in a single analytical run for the diagnosis of fatty-acid oxidation disorders, organic acidurias, and aminoacidurias. Published diagnostic criteria for these disorders normally incorporate a primary metabolic marker combined with secondary markers, often analyte ratios, for which the markers have been chosen to reflect metabolic pathway deviations.

METHODS

We applied a procedure to extract new markers and diagnostic criteria for newborn screening to the data of newborns with confirmed medium-chain acyl-CoA dehydrogenase deficiency (MCADD) and a control group from the newborn screening program, Heidelberg, Germany. We validated the results with external data of the screening center in Hamburg, Germany. We extracted new markers by performing a systematic search for analyte combinations (features) with high discriminatory performance for MCADD. To select feature thresholds, we applied automated procedures to separate controls and cases on the basis of the feature values. Finally, we built classifiers from these new markers to serve as diagnostic criteria in screening for MCADD.

RESULTS

On the basis of chi(2) scores, we identified approximately 800 of >628,000 new analyte combinations with superior discriminatory performance compared with the best published combinations. Classifiers built with the new features achieved diagnostic sensitivities and specificities approaching 100%.

CONCLUSION

Feature construction methods provide ways to disclose information hidden in the set of measured analytes. Other diagnostic tasks based on high-dimensional metabolic data might also profit from this approach.

The epidemiology of medium chain acyl-CoA dehydrogenase deficiency: an update

The most common fatty acid oxidation disorder, medium chain acyl-CoA dehydrogenase deficiency (MCADD), has become the focal point for the adoption of tandem mass spectrometry to detect it and related inborn errors of metabolism. This article updates a human genome epidemiology review of MCADD published in 1999. The focus of this update is on epidemiologic parameters rather than mutations associated with MCADD. Currently available information from screening studies on the frequency of detection of MCADD in newborns, as well as the frequency of homozygotes for the common mutation in the ACADM gene, is summarized. In the United States, the average incidence of the disorder is from 1 in 15,000 to 1 in 20,000 births, with individual states reporting frequencies from 1 in 10,000 to 1 in 30,000 births. In addition, a systematic review was undertaken of the published literature on the frequency of mortality and developmental disabilities among children with MCADD, both in screened and unscreened cohorts. It seems that in the absence of newborn screening for MCADD, premature death or serious disability occurs in 20% to 25% of children with the disorder. Systematic collection and analysis of follow-up data are still needed to ascertain the frequencies of outcomes in screened cohorts.

Economics of tandem mass spectrometry screening of neonatal inherited disorders

Objectives:The aim of this study was to evaluate the cost-effectiveness of neonatal screening for phenylketonuria (PKU) and medium-chain acyl-coA dehydrogenase (MCAD) deficiency using tandem mass spectrometry (tandem MS).

Methods:A systematic review of clinical efficacy evidence and cost-effectiveness modeling of screening in newborn infants within a UK National Health Service perspective was performed. Marginal costs, life-years gained, and cost-effectiveness acceptability curves are presented.

Results:Substituting the use of tandem MS for existing technologies for the screening of PKU increases costs with no increase in health outcomes. However, the addition of screening for MCAD deficiency as part of a neonatal screening program for PKU using tandem MS, with an operational range of 50,000 to 60,000 specimens per system per year, would result in a mean incremental cost of −£17,298 (−£129,174, £66,434) for each cohort of 100,000 neonates screened. This cost saving is associated with a mean incremental gain of 57.3 (28.0, 91.4) life-years.

Conclusions:Cost-effectiveness analysis using economic modeling indicates that substituting the use of tandem MS for existing technologies for the screening of PKU alone is not economically justified. However, the addition of screening for MCAD deficiency as part of a neonatal screening program for PKU using tandem MS would be economically attractive.

Na+, K+ ATPase activity is markedly reduced by cis-4-decenoic acid in synaptic plasma membranes from cerebral cortex of rats

We have previously demonstrated that octanoic (OA) and decanoic acids (DA) inhibit Na+, K+ ATPase activity in synaptic plasma membranes from rat brain. The objective of the present study was to investigate the in vitro effects of the other metabolites that accumulate in tissues of medium-chain acyl-CoA dehydrogenase (MCAD)-deficient patients, namely cis-4-decenoic acid (cDA), octanoylcarnitine (OC), hexanoylcarnitine (HC), hexanoylglycine (HG), phenylpropionylglycine (PPG) and suberoylglycine (SG), on Na+, K+ ATPase activity in synaptic plasma membrane from cerebral cortex of 30-day-old rats. cDA, the pathognomonic compound found in this disorder, provoked the strongest inhibition on this enzyme activity at concentrations as low as 0.25 mM, whereas OC inhibited this activity at 1.0 mM and higher concentrations in a dose-dependent manner. In contrast, HC, HG, PPG and SG did not affect Na+, K+ ATPase activity. Furthermore, pre-treatment of cortical homogenates with the antioxidant enzymes catalase plus superoxide dismutase totally prevented cDA-induced Na+, K+ ATPase inhibition. We also provided evidence that cDA, as well as OA and DA, caused lipid peroxidation, which may explain, at least in part, the inhibitory properties of these compounds towards Na+, K+ ATPase. Considering that Na+, K+ ATPase is a critical enzyme for normal brain development and functioning, it is presumed that these findings, especially those regarding to the marked inhibitory effect of cDA, may be involved in the pathophysiology of the neurological dysfunction of MCAD-deficient 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.

A biochemical perspective on the use of tandem mass spectrometry for newborn screening and clinical testing

The first newborn screen was a clinical test to detect a disorder of the biochemistry of the amino acid, phenylalanine. This disorder, known as phenylketonuria, produces profound mental retardation if not detected and treated early in life. Early screening programs relied on inexpensive population screening techniques that have all but been replaced by more accurate analytical methods such as tandem mass spectrometry (MS/MS). MS/MS enables a multianalyte approach for detecting biochemical disorders such that a metabolic profile is obtained rather than a single analyte measurement. The metabolic profile has clearly shown improvements in the detection of diseases such as phenylketonuria and several new disorders arising from errors in fatty acid oxidation and organic acid metabolism. MS/MS is a powerful tool for accessing the metabolic status of a newborn and can detect both inborn metabolic errors as well as examine the effect of acquired diseases or pharmacologic intervention on intermediary metabolism.

Homozygosity for a severe novel medium-chain acyl-CoA dehydrogenase (MCAD) mutation IVS3-1G > C that leads to introduction of a premature termination codon by complete missplicing of the MCAD mRNA and is associated with phenotypic diversity ranging from sudden neonatal death to asymptomatic status

Virtually all patients with medium-chain acyl-CoA dehydrogenase deficiency (MCADD) are homozygous or compound heterozygous for the 985A > G mutation, which limits the study of a possible genotype/phenotype correlation. A newborn Palestinian infant died suddenly on the second day of life. A previous sibling had also died in similar circumstances aged 3 weeks. Urine organic acid and bloodspot acylcarnitine analysis were consistent with MCADD. He was homozygous for a novel MCAD splice mutation, IVS3-1G > C. This mutation leads to deletion of 7 bp and introduction of a premature termination codon as a result of complete missplicing of MCAD mRNA. This misspliced MCAD mRNA encodes a non-functional protein and is furthermore reduced in amounts due to nonsense-mediated decay, resulting in total lack of functional MCAD enzyme. This is the first molecular identification of MCADD in an Arab patient and the first reported splice mutation in the MCAD gene that has been functionally characterized. The association of homozygosity for a null mutation with lethal neonatal presentation in the index patient and presumably the previous infant suggested a genotype/phenotype correlation. However, a 6-year-old completely asymptomatic sibling also had the characteristic MCADD biochemical phenotype and was homozygous for the same IVS3-1G > C mutation. As a first candidate to modify the disease presentation, by modulating the overlapping enzyme activity, we tested the entire family for the prevalent SCAD gene 625G > A susceptibility variant. Interestingly, all family members were 625G > A homozygous. Additional genetic and/or environmental factors must play a major role in determining the phenotypic diversity of MCADD.

Pseudo-glutarylcarnitinaemia in medium-chain acyl-CoA dehydrogenase deficiency detected by tandem mass spectrometry newborn screening

As well as characteristic increases in C(8) carnitine, dried blood spot samples from 11 newborns with medium-chain acyl-CoA dehydrogenase deficiency detected by tandem mass spectrometry screening using butyl esters showed apparent increases in glutarylcarnitine (m / z 388 signals). In four of the newborns in which it was measured, apparent increases in malonylcarnitine (m / z 360) were also detected. It was shown that the apparent increases were caused by interfering acylcarnitines, putatively identified as hydroxyoctanoylcarnitine and hydroxydecanoylcarnitine, respectively, using alternative derivatives for tandem mass spectrometry. Levels of the two abnormal carnitines correlated with C(8) carnitine levels and normalized with repeat testing in 10 cases. These results indicated that the abnormal carnitines were significantly elevated only during periods of increased fatty acid catabolism, as may occur in the immediate postnatal period.

Newborn screening for medium chain acyl-CoA dehydrogenase deficiency: evaluating the effects on outcome

Although individually rare, inborn errors of metabolism represent a potentially preventable cause of death and disability. Tandem mass spectrometry allows a number of these disorders to be detected in a single step. Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most important of these disorders. However, public health decisions on whether or not to implement new screening programmes rely on evidence regarding benefits and harms. This article reviews existing published evidence for newborn screening for MCADD and highlights where further information is required for public health decision making. This review reveals that important uncertainties remain about performance and outcome, including criteria and thresholds for defining a positive screening result, diagnostic criteria, test performance and longer-term outcome. Notably, despite a combined experience of screening well over one million infants, there has been no report of a systematic follow-up of longer-term outcome in affected infants detected by screening. Prospective data on mortality, neurological outcome, and cognitive function are required to assess the effectiveness of screening. Additionally, the impact of screening and treatment on the families of infants with true, borderline, and false positive diagnoses needs to be taken into account.

Use of tandem mass spectrometry for multianalyte screening of dried blood specimens from newborns

BACKGROUND

Over the past decade laboratories that test for metabolic disorders have introduced tandem mass spectrometry (MS/MS), which is more sensitive, specific, reliable, and comprehensive than traditional assays, into their newborn-screening programs. MS/MS is rapidly replacing these one-analysis, one-metabolite, one-disease classic screening techniques with a one-analysis, many-metabolites, many-diseases approach that also facilitates the ability to add new disorders to existing newborn-screening panels.

METHODS

During the past few years experts have authored many valuable articles describing various approaches to newborn metabolic screening by MS/MS. We attempted to document key developments in the introduction and validation of MS/MS screening for metabolic disorders. Our approach used the perspective of the metabolite and which diseases may be present from its detection rather than a more traditional approach of describing a disease and noting which metabolites are increased when it is present.

CONTENT

This review cites important historical developments in the introduction and validation of MS/MS screening for metabolic disorders. It also offers a basic technical understanding of MS/MS as it is applied to multianalyte metabolic screening and explains why MS/MS is well suited for analysis of amino acids and acylcarnitines in dried filter-paper blood specimens. It also describes amino acids and acylcarnitines as they are detected and measured by MS/MS and their significance to the identification of specific amino acid, fatty acid, and organic acid disorders.

CONCLUSIONS

Multianalyte technologies such as MS/MS are suitable for newborn screening and other mass screening programs because they improve the detection of many diseases in the current screening panel while enabling expansion to disorders that are now recognized as important and need to be identified in pediatric medicine.

MS/MS-based newborn and family screening detects asymptomatic patients with very-long-chain acyl-CoA dehydrogenase deficiency

OBJECTIVES

To determine whether asymptomatic persons with biochemical evidence of very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency identified through expanded newborn screening with tandem mass spectometry have confirmed disease.

STUDY DESIGN

We characterized 8 asymptomatic VLCAD-deficient individuals by enzyme and/or mutational analysis and compared them with clinically diagnosed, symptomatic patients with regard to mutations, enzyme activity, phenotype, and age of disease onset.

RESULTS

VLCAD molecular analyses in 6 unrelated patients revealed the previously reported V243A mutation, associated with hepatic or myopathic phenotypes, on 7/12 alleles. All other mutations were also missense mutations. Residual VLCAD activities of 6% to 11% of normal were consistent with milder phenotypes. In these identified individuals treated prospectively with dietary modification as preventive measures, clinical symptoms did not develop during follow-up.

CONCLUSIONS

MS/MS-based newborn screening correctly identifies VLCAD-deficient individuals. Based on mutational and enzymatic findings, these infants probably are at risk of future disease. Because life-threatening metabolic derangement can occur even in otherwise mild phenotypes, we advocate universal newborn screening programs for VLCAD deficiency to detect affected patients and prevent development of metabolic crises. Longer-term follow-up is essential to define outcomes, the definite risk of future disease, and appropriate treatment recommendations.

Accurate measurement of free carnitine in dried blood spots by isotope-dilution electrospray tandem mass spectrometry without butylation

BACKGROUND

To test the feasibility of free carnitine (FC) determination in dried blood spot specimens (DBS) by stable isotope-dilution electrospray-ionisation tandem mass spectrometry (MS/MS).

METHODS

The MS/MS method established for newborn screening, measuring acylcarnitines by positive precursor ion scan of m/z 85 in DBS, was adapted by omitting the butylation and heating step during sample preparation. FC measurement in DBS by this non-butylating MS/MS assay was compared with the butylating MS/MS method and the spectrophotometric Cobas method.

RESULTS

FC measurement by the non-butylating MS/MS method meets the demands for a bioanalytical microassay with respect to linearity, detection limit (LOD), accuracy, and precision. Formation of FC was 0-1% and 1-4% in liquid samples and in DBS by the non-butylating MS/MS method, while 3-10% and 8-16% by the butylating method, respectively. Acid-catalysed hydrolysis (butanolysis) in liquid samples was higher for short-chain acylcarnitines (acetyl- and propionylcarnitine). Hydrolysis in DBS was more pronounced for long-chain acylcarnitines. FC concentrations in healthy newborns without butylation were 35% lower than those measured by the established newborn screening assay.

CONCLUSIONS

The non-butylating MS/MS assay provides a simple and accurate method for FC determination in DBS and represents a trivial but important adaptation of a method already used in many laboratories.

Expanded newborn screening for inborn errors of metabolism by electrospray ionization-tandem mass spectrometry: results, outcome, and implications

OBJECTIVE

The aims of this study were to determine the impact of expanded newborn screening using tandem mass spectrometry (MS/MS) on the overall detection rate of inborn errors of metabolism in Germany and to assess the outcome for the patients that were diagnosed.

METHODS

During the period of study, 250,000 neonates in a German population were investigated for 23 inborn errors of metabolism by electrospray ionization-MS/MS. The overall value of the screening program was estimated by 1) complete ascertainment of all positive tests; 2) definite assignment of all diagnoses including reconfirmation at 12 months; and 3) clinical follow-up of all detected patients in an overall interval of 42 months. The mean observation period was 13.5 months per child.

RESULTS

In 106 newborns, confirmed inborn errors of metabolism were found. The disorders were classified as 50 classic forms and 56 variants. A total of 825 tests (0.33%) were false-positives. Seventy of the 106 newborns with confirmed disorders were judged to require treatment. Six children developed symptoms despite treatment. Three children had died. Among 9 children who became symptomatic before report of the results of screening, in 6 the diagnosis had been made in advance of the screening report. In evaluation of the screening program, 61 of the 106 identified children (58% of true-positives, or 1 of 4100 healthy newborns) were judged to have benefited from screening and treatment, because the diagnosis had not been made before screening. None of these infants had died and none developed psychomotor retardation or metabolic crisis during the follow-up period.

CONCLUSIONS

The screening by MS/MS for up to 23 additional disorders has approximately doubled the detection rate compared with that achieved by the conventional methods used in Germany. This strategy represents valuable preventive medicine by enabling diagnosis and treatment before the onset of symptoms.

Neonatal screening of inborn errors of metabolism using tandem mass spectrometry: an evidence-based analysis

OBJECTIVES AND METHOD

The Medical Advisory Secretariat undertook a review of the evidence on the effectiveness and cost-effectiveness of using tandem mass spectrometer [MS/MS] for the neonatal screening of inborn errors of metabolism [IEM]. The review is based on two systematic reviews commissioned by the National Health Services (United Kingdom) and relevant research literature that was published after the completion of these two systematic reviews. A horizon scanning was conducted to determine the current status of neonatal screening programs in other national and international jurisdictions. The MAS also consulted with stakeholders including the laboratory branch, an expert in IEM at a pediatric hospital, MS/MS experts and a MS/MS manufacturer.

RESULT

Synthesis of information obtained from the above process showed that: Ontario is currently screening all newborns for phenylketonuria [PKU] and congenital hypothyroidism [CH] using the Guthrie method on dry blood spots obtained by heel prick before discharge from hospital.MS/MS can detect 25 IEMs in a single process on the same dry blood spot.Computer algorithms have been used to automate the MS/MS screening process to provide rapid throughputs of 400 samples or more per day. Screening for additional IEMs using MS/MS does not add significant cost to the program.MS/MS -based neonatal screening showed sensitivity of 100% and specificity of 83% to 99% depending on the IEM. The specificity of MS/MS in detecting PKU is significantly superior to that of the current Guthrie method and is therefore able to reduce the number of false positive results.For certain inborn errors of metabolism not currently screened, early detection and simple treatment could avoid early mortality and prevent or reduce mental retardationUsing eligibility criteria recommended by the World Health Organization adapted to Ontario, a rating system was developed and applied to assess the IEMs recommended for inclusion in neonatal screening.The assessment showed that PKU and CH should continued to be screened. In addition, medium chain acyl-CoA dehydrogenase deficiency [MCADD] and congenital adrenal hyperplasia [CAH] met most of the criteria for inclusion in a neonatal screening program. MCADD can be screened with PKU by MS/MS while the test for CAH requires a different methodology.An expanded neonatal program would require an enhanced infrastructure for result interpretation, reporting, care provision and counseling.Important ethical and societal issues including informed consent need to be addressed.As of 1998, twenty-six states in the United States were using MS/MS for newborn screening of IEMs. In Canada, British Columbia, Saskatchewan and Nova Scotia use MS/MS for IEM related assays. Manitoba is planning to implement MS/MS -based neonatal screening in 2003.Among Canadian jurisdictions, British Columbia, Manitoba, Quebec, Nova Scotia and Saskatchewan are screening for more IEMs than Ontario.

Determination of carnitine and acylcarnitines in urine by high-performance liquid chromatography-electrospray ionization ion trap tandem mass spectrometry

A high-performance liquid chromatography-mass spectrometry method has been developed for the simultaneous determination of native carnitine and eight acylcarnitines in urine. The procedure uses a solid-phase extraction on a cation-exchange column and the separation is performed without derivatization within 17 min on a reversed-phase C8 column in the presence of a volatile ion-pairing reagent. The detector was an ion trap mass spectrometer and quantification was carried out in the MS-MS mode. Validation was done for aqueous standards at ranges between 0.75 and 200 micromol/l, depending on the compound. Carnitine was quantified in urine and comparison with a radioenzymatic assay gave a satisfactory correlation (R2 = 0.981). The assay could be successfully applied to the diagnostic of pathological acylcarnitines profile of metabolic disorders in urines of patients suffering from different organic acidurias.

Strategies for the diagnosis of mitochondrial fatty acid beta-oxidation disorders

Mitochondrial fatty acid beta-oxidation disorders (FAOD) are a group of clinically and biochemically heterogeneous inherited metabolic defects. The spectrum of phenotypes has expanded from hepatic encephalopathy to encompass myopathy, cardiomyopathy, peripheral neuropathy, sudden death and pregnancy complicated by fetal FAOD. Pre-symptomatic diagnosis is important to prevent morbidity and this is now achievable through newborn screening using tandem mass spectrometry (MS/MS). Moreover, most of the diagnosed defects are treatable and the prognosis is generally favourable. This article reviews the features of FAOD, critically evaluates methods of investigation including metabolite analyses in body fluids, in vitro oxidation rates and acylcarnitine profiling studies, enzymatic and mutational tests, and discusses genotype-phenotype correlation, treatment and monitoring options. Based on this knowledge, strategies for the biochemical investigation and differential diagnosis of patients presenting clinically, asymptomatic neonates detected by newborn screening, infants born after complications during late pregnancy, and cases of sudden death with suspected FAOD are presented. Laboratory investigation commonly begins with a search for diagnostic metabolites in physiological fluids, followed by in vitro functional studies if the initial findings are inconclusive, and confirmation by enzymology and molecular analyses. Occasionally a stress test in vivo may be required. At other times there may be no firm diagnosis achieved.

Newborn mass screening and selective screening using electrospray tandem mass spectrometry in Japan

Electrospray tandem mass spectrometry was applied to detect a series of inherited metabolic disorders during a newborn-screening pilot study and a selective screening in Japan. In our mass screening of 102,200 newborns, five patients with propionic acidemia, two with methylmalonic acidemia, two with medium-chain acyl-CoA dehydrogenase deficiency, three with citrullinemia type II, and one with phenylketonuria were identified. In a selective screening of 164 patients with symptoms mainly related to hypoglycemia and/or hyperammonemia, 12 with fatty acid oxidation disorders and six with other disorders were found. The results indicated the importance of newborn screening using this technology in Japan.

Very high compliance in an expanded MS-MS-based newborn screening program despite written parental consent

OBJECTIVES

In Bavaria, Germany, an expanded MS-MS-based newborn screening program was implemented in 1999. The coverage of new additional conditions and novelty of technology required introduction of written parental consent. Here we evaluated the influence of the consent procedure on compliance by systematic demographic tracking.

METHODS

Comprehensive information was provided for parents, professionals, and the public. Screening notifications were matched with all birth notifications on name and date of birth. Parents of children without screening notification were contacted and counseled.

RESULTS

Between August 1, 1999, and July 31, 2000, 123,284 children eligible for screening were born. Of these, 116,652 were matched successfully. Among 6,632 parents contacted, 2,516 (2%) did not respond. Three thousand thirty-four children were screened but the parents initially refused to participate in tracking. Five hundred ninety-four were screened outside the program. Four hundred eighty-eight untested newborns were identified. Three hundred twenty-five screening failures due to logistic problems were tested subsequently. Screening was definitely refused by the parents of 163 children (0.1% of target population).

CONCLUSIONS

With appropriate information provided and surveillance by tracking, high compliance with newborn screening can be achieved despite a written consent requirement.

Rapid Liquid Chromatography-Tandem Mass Spectrometry Method for Routine Analysis of Cyclosporin A Over an Extended Concentration Range

Background: Cyclosporin A (CsA) is commonly measured by immunoassay techniques that have a limited analytical range. The consequence of this is that low CsA concentrations that may be clinically significant are difficult to measure and that high concentrations require sample dilution, which introduces error and increases cost. More specific assays, such as HPLC, do not have the required turnaround times for busy transplant clinics.

Methods: CsA was measured in whole blood from 180 cardiac and lung transplant recipients by a liquid chromatography-tandem mass spectrometry (MS) assay, and the results were compared with the Dade Behring Emit assay. Proteins were precipitated with acetonitrile containing ascomycin as internal standard. We used isocratic elution on a Supelco CN column (33 × 3.0 mm; 3- μm bead size) with a mobile phase of 65% aqueous acetonitrile containing ammonium acetate (2 mmol/L) and formic acid (1 g/L), at a flow rate of 0.5 mL/min, with a sample injection volume of 6 μL. We used positive-ion electrospray MS to monitor the ammonium adducts of the compounds of interest decomposing under controlled conditions to the most dominant fragments of the individual molecules. Calibration curves used linear least-squares regression with 1/x weighting.

Results: Maximum sensitivity was obtained by monitoring fragmentation of the ammonium adducts m/z 1220→m/z 1203 for CsA and m/z 809→m/z 765 for ascomycin. Sample throughput, including preparation time, was 30 samples in 1.5 h with an injection-to-injection cycle time of 1.5 min. The calibration curve was linear to 5000 μg/L, with a detection limit of 0.03 μg/L and a limit of quantification of 1 μg/L. Regression analysis [tandem MS method (y) and Emit assay (x)] yielded a slope of 1.09 (± 0.03), an intercept of 6.2 (± 4.5) μg/L, and Sy|x = 27 μg/L.

Conclusions: Tandem MS assay is a realistic alternative to immunoassay for the routine monitoring of CsA in transplant recipients. Its wide dynamic range has utility for pharmacokinetic studies of CsA.

Laboratory approach to mitochondrial diseases

Dysfunction in mitochondrial processes has been related to several pathologies. In these disorders, the cell suffers oxidative imbalance that is mostly due to defects in pyruvate metabolism, mitochondrial fatty acids oxidation, the citric acid cycle or electron transport by the mitochondrial respiratory chain. These metabolic alterations produce mitochondrial diseases that have been related to inherited syndromes, such as MERRF or MELAS. The main affected organs are brain, skeletal muscle, kidney, heart and liver, because of the high energetic demand and the oxidative metabolism. Moreover, the relationship between mitochondrial dysfunction and neurodegenerative processes, such as Parkinson disease or Alzheimer disease, as well as ageing, has been shown. Because mitochondrias are the target of several xenobiotics, such as aspirin, AZT or alcohol consumption, mitochondrial impairment has also been proposed as a mechanism of toxicity. Most laboratory tests that are available in the diagnosis of mitochondrial illness are assayed in tissue biopsies and are usually difficult to interpret. Recently, it has been shown that non-invasive techniques, such as nuclear magnetic resonance or the 2-keto[1-(13)C]isocaproic acid breath test, may be useful to assess mitochondrial function. This article attempts to show the laboratory approach to mitochondrial diseases, reviewing new techniques that could be of great value in the research of mitochondrial function, such as the 2-keto[1-(13)C]isocaproic breath test.

Evaluation of newborn screening for medium chain acyl-CoA dehydrogenase deficiency in 275 000 babies

OBJECTIVE

To evaluate newborn screening by tandem mass spectrometry for detection of medium chain acyl-CoA dehydrogenase (MCAD) deficiency, a fatty acid oxidation disorder with significant mortality in undiagnosed patients.

DESIGN

The following were studied: (a) 13 clinically detected MCAD deficient subjects, most homozygous for the common A985G mutation, whose newborn screening sample was available; (b) 275 653 consecutive neonates undergoing routine newborn screening. Screened infants with blood octanoylcarnitine levels > or = 1 micromol/l were analysed for the A985G mutation, had analysis of plasma and repeat blood spot acylcarnitines and urinary organic acids, and had fibroblast fatty acid oxidation or acylcarnitine studies.

RESULT

Twelve of the 13 patients later diagnosed clinically had newborn octanoylcarnitine levels > 2.3 micromol/l. Twenty three screened babies had initial octanoylcarnitine levels > or = 1 micromol/l. Eleven of 12 babies with persistent abnormalities had metabolite and/or enzyme studies indicating MCAD deficiency. Only four were homozygous for the A985G mutation, the remainder carrying one copy.

CONCLUSIONS

Most patients with symptomatic MCAD deficiency could be detected by newborn screening. Infants actually detected had a lower frequency of A985G alleles than clinically diagnosed cases and may have a lower risk of becoming symptomatic.

Clinical applications of tandem mass spectrometry: ten years of diagnosis and screening for inherited metabolic diseases

This paper reviews the clinical applications of tandem mass spectrometry (MS-MS) in diagnosis and screening for inherited metabolic diseases in the last 10 years. The broad-spectrum of diseases covered, specificity, ease of sample preparation, and high throughput provided by the MS-MS technology has led to the development of multi-disorder newborn screening programs in many countries for amino acid disorders, organic acidemias, and fatty acid oxidation defects. Issues related to sample acquisition, sample preparation, quantification of metabolites, and validation are discussed. Our current experience with the technique in screening is presented. The application of MS-MS in selective screening has revolutionized the field and made a major impact on the detection of certain disease classes such as the fatty acid oxidation defects. New specific and rapid MS-MS and LC-MS-MS methods for highly polar small molecules are supplementing or replacing some of the classical GC-MS methods for a multitude of metabolites and disorders. New exciting applications are appearing in fields of prenatal, postnatal, and even postmortem diagnosis. Examples for pitfalls in the technique are also presented.

Medium-chain acyl-CoA dehydrogenase (MCAD) mutations identified by MS/MS-based prospective screening of newborns differ from those observed in patients with clinical symptoms: identification and characterization of a new, prevalent mutation that results in mild MCAD deficiency

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the most frequently diagnosed mitochondrial beta-oxidation defect, and it is potentially fatal. Eighty percent of patients are homozygous for a common mutation, 985A-->G, and a further 18% have this mutation in only one disease allele. In addition, a large number of rare disease-causing mutations have been identified and characterized. There is no clear genotype-phenotype correlation. High 985A-->G carrier frequencies in populations of European descent and the usual avoidance of recurrent disease episodes by patients diagnosed with MCAD deficiency who comply with a simple dietary treatment suggest that MCAD deficiency is a candidate in prospective screening of newborns. Therefore, several such screening programs employing analysis of acylcarnitines in blood spots by tandem mass spectrometry (MS/MS) are currently used worldwide. No validation of this method by mutation analysis has yet been reported. We investigated for MCAD mutations in newborns from US populations who had been identified by prospective MS/MS-based screening of 930,078 blood spots. An MCAD-deficiency frequency of 1/15,001 was observed. Our mutation analysis shows that the MS/MS-based method is excellent for detection of MCAD deficiency but that the frequency of the 985A-->G mutant allele in newborns with a positive acylcarnitine profile is much lower than that observed in clinically affected patients. Our identification of a new mutation, 199T-->C, which has never been observed in patients with clinically manifested disease but was present in a large proportion of the acylcarnitine-positive samples, may explain this skewed ratio. Overexpression experiments showed that this is a mild folding mutation that exhibits decreased levels of enzyme activity only under stringent conditions. A carrier frequency of 1/500 in the general population makes the 199T-->C mutation one of the three most prevalent mutations in the enzymes of fatty-acid oxidation.

Hypoglycemia in association with various organic and amino acid disorders

A number of organic and amino acidemias, particularly those that involve the oxidation of fatty acids, cause hypoglycemia intermittently. This may be associated with distrubances of acid base equilibrium and accumulation of lactic acid and/or ketone bodies. When such diseases are not diagnosed rapidly, they might lead to neurological crippling and, at times, death. As a group, these disorders involve more than 1 organ and their phenotypic expression may include all or a single system. The symptoms may appear soon after birth or as late as 1 year of age. Their early recognition and rapid intervention provide rewarding clinical outcome. With the recent advances in diagnostic techniques, such as the introduction of tandem mass spectrometry (MS), screening for these diseases now can be performed because rapid identification on a large scale is possible. The phenotypes, mutations involved, pathognomonic laboratory findings, prognosis, and treatment procedures available have been reviewed for major diseases.

Tandem mass spectrometry screening: proving effectiveness

Despite the considerable literature now emerging on screening by tandem mass spectrometry there are many points of uncertainty about test performance and much work to do in formalizing and validating follow-up protocols. The relative sensitivities of tandem mass spectrometry and previously-used diagnostic methods may differ for some diseases but not others, with the possibility of some metabolites being over-sensitive and diagnosing mild variants or non-disease. Cut-offs should be set using clinical rather than analytical criteria and at this early stage it is important that presumptive positive cases diagnosed through acylcarnitine profiling are compared as thoroughly as possible with symptomatic cases diagnosed using other techniques. Caution should be used in accepting mutation analysis as the ultimate diagnostic criterion. Consideration of incidence and careful examination of family history will all contribute to evidence of the equivalence or otherwise of screen-detected and symptomatic disease. Finally, there should be registration and long-term surveillance of all cases detected.

Population newborn screening for inherited metabolic disease: current UK perspectives

Some of the generally accepted criteria for screening programmes are inappropriate for newborn metabolic screening as they ignore the family dimension and the importance of timely genetic information. Uncritical application of such criteria creates special difficulties for screening by tandem mass spectrometry, which can detect a range diseases with widely different natural histories and responsiveness to treatment. Further difficulties arise from increasing demands for direct proof of the effects of screening on long-term morbidity and mortality. The randomized controlled trial is held to be the gold standard, but for ethical and practical reasons it will be impossible to achieve for such relatively rare diseases. This approach also oversimplifies the complex matrix of costs and benefits of newborn metabolic screening. A more workable approach could involve Bayesian synthesis, combining quantitative performance data from carefully designed prospective pilot studies of screening with existing experience of the natural history, diagnosis, and management of the individual disorders concerned.

Outcome of medium chain acyl-CoA dehydrogenase deficiency after diagnosis

BACKGROUND

Medium chain acyl-CoA dehydrogenase (MCAD) deficiency is the most common inborn error of fatty acid metabolism. Undiagnosed, it has a mortality rate of 20-25%. Neonatal screening for the disorder is now possible but it is not known whether this would alter the prognosis.

OBJECTIVE

To investigate the outcome of MCAD deficiency after the diagnosis has been established.

METHOD

All patients with a proved diagnosis of MCAD deficiency attending one centre in a four year period were reviewed.

RESULTS

Forty one patients were identified. Follow up was for a median of 6.7 years (range, 9 months to 14 years). Nearly half of the patients were admitted to hospital with symptoms characteristic of MCAD deficiency before the correct diagnosis was made. After diagnosis, two patients were admitted to hospital with severe encephalopathy but there were no additional deaths or appreciable morbidity. There was a high incidence (about one fifth) of previous sibling deaths among the cohort.

CONCLUSIONS

Undiagnosed, MCAD deficiency results in considerable mortality and morbidity. However, current management improves outcome, supporting the view that the disorder should be included in newborn screening programmes.