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

221 newborn-screened neonates with medium-chain acyl-coenzyme A dehydrogenase deficiency: Findings from the Inborn Errors of Metabolism Collaborative

INTRODUCTION

There is limited understanding of relationships between genotype, phenotype and other conditions contributing to health in neonates with medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD) identified through newborn screening.

METHODS

Retrospective analysis of comprehensive data from a cohort of 221 newborn-screened subjects identified as affected with MCADD in the Inborn Errors of Metabolism - Information System (IBEM-IS), a long term follow-up database of the Inborn Errors of Metabolism Collaborative, was performed.

RESULTS

The average age at notification of first newborn screen results to primary care or metabolic providers was 7.45days. The average octanoylcarnitine (C8) value on first newborn screen was 11.2μmol/L (median 8.6, range 0.36-43.91). A higher C8 level correlated with an earlier first subspecialty visit. Subjects with low birth weight had significantly lower C8 values. Significantly higher C8 values were found in symptomatic newborns, in newborns with abnormal lab testing in addition to newborn screening and/or diagnostic tests, and in subjects homozygous for the c.985A>G ACADM gene mutation or compound heterozygous for the c.985A>G mutation and deletions or other known highly deleterious mutations. Subjects with neonatal symptoms, or neonatal abnormal labs, or neonatal triggers were more likely to have at least one copy of the severe c.985A>G ACADM gene mutation. C8 and genotype category were significant predictors of the likelihood of having neonatal symptoms. Neonates with select triggers were more likely to have symptoms and laboratory abnormalities.

CONCLUSIONS

This collaborative study is the first in the United States to describe health associations of a large cohort of newborn-screened neonates identified as affected with MCADD. The IBEM-IS has utility as a platform to better understand the characteristics of individuals with newborn-screened conditions and their follow-up interactions with the health system.

The Frequencies of Different Inborn Errors of Metabolism in Adult Metabolic Centres: Report from the SSIEM Adult Metabolic Physicians Group

BACKGROUND

There are few centres which specialise in the care of adults with inborn errors of metabolism (IEM). To anticipate facilities and staffing needed at these centres, it is of interest to know the distribution of the different disorders.

METHODS

A survey was distributed through the list-serve of the SSIEM Adult Metabolic Physicians group asking clinicians for number of patients with confirmed diagnoses, types of diagnoses and age at diagnosis.

RESULTS

Twenty-four adult centres responded to our survey with information on 6,692 patients. Of those 6,692 patients, 510 were excluded for diagnoses not within the IEM spectrum (e.g. bone dysplasias, hemochromatosis) or for age less than 16 years, leaving 6,182 patients for final analysis. The most common diseases followed by the adult centres were phenylketonuria (20.6%), mitochondrial disorders (14%) and lysosomal storage disorders (Fabry disease (8.8%), Gaucher disease (4.2%)). Amongst the disorders that can present with acute metabolic decompensation, the urea cycle disorders, specifically ornithine transcarbamylase deficiency, were most common (2.2%), followed by glycogen storage disease type I (1.5%) and maple syrup urine disease (1.1%). Patients were frequently diagnosed as adults, particularly those with mitochondrial disease and lysosomal storage disorders.

CONCLUSIONS

A wide spectrum of IEM are followed at adult centres. Specific knowledge of these disorders is needed to provide optimal care including up-to-date knowledge of treatments and ability to manage acute decompensation.

Newborn screening for medium-chain acyl-CoA dehydrogenase deficiency: regional experience and high incidence of carnitine deficiency

Background

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most common inherited defect in the mitochondrial fatty acid oxidation pathway, resulting in significant morbidity and mortality in undiagnosed patients.

Newborn screening (NBS) has considerably improved MCADD outcome, but the risk of complication remains in some patients. The aim of this study was to evaluate the relationship between genotype, biochemical parameters and clinical data at diagnosis and during follow-up, in order to optimize monitoring of these patients.

Methods

We carried out a multicenter study in southwest Europe, of MCADD patients detected by NBS. Evaluated NBS data included free carnitine (C0) and the acylcarnitines C8, C10, C10:1 together with C8/C2 and C8/C10 ratios, clinical presentation parameters and genotype, in 45 patients. Follow-up data included C0 levels, duration of carnitine supplementation and occurrence of metabolic crises.

Results

C8/C2 ratio and C8 were the most accurate biomarkers of MCADD in NBS. We found a high number of patients homozygous for the prevalent c.985A > G mutation (75%). Moreover, in these patients C8, C8/C10 and C8/C2 were higher than in patients with other genotypes, while median value of C0 was significantly lower (23 μmol/L vs 36 μmol/L).

The average follow-up period was 43 months. To keep carnitine levels within the normal range, carnitine supplementation was required in 82% of patients, and for a longer period in patients homozygotes for the c.985A>G mutation than in patients with other genotypes (average 31 vs 18 months). Even with treatment, median C0 levels remained lower in homozygous patients than in those with other genotypes (14 μmol/L vs 22 μmol/L).

Two patients died and another three suffered a metabolic crisis, all of whom were homozygous for the c.985 A>G mutation.

Conclusions

Our data show a direct association between homozygosity for c.985A>G and lower carnitine values at diagnosis, and a higher dose of carnitine supplementation for maintenance within the normal range. This study contributes to a better understanding of the relationship between genotype and phenotype in newborn patients with MCADD detected through screening which could be useful in improving follow-up strategies and clinical outcome.

Clinical and molecular aspects of Japanese children with medium chain acyl-CoA dehydrogenase deficiency

We report the outcome of 16 Japanese patients with medium chain acyl-CoA dehydrogenase deficiency. Of them, 7 patients were diagnosed after metabolic crisis, while 9 were detected in the asymptomatic condition. Of the 7 symptomatic cases, 1 died suddenly, and 4 cases had delayed development. All 9 patients identified by neonatal or sibling screening remained healthy. Of 14 mutations identified, 10 were unique for Japanese, and 4 were previously reported in other nationalities. Presymptomatic detection including neonatal screening obviously improves quality of life of Japanese patients, probably regardless of the genotypes.

Cost-effectiveness analysis of universal newborn screening for medium chain acyl-CoA dehydrogenase deficiency in France

BACKGROUND

Five diseases are currently screened on dried blood spots in France through the national newborn screening programme. Tandem mass spectrometry (MS/MS) is a technology that is increasingly used to screen newborns for an increasing number of hereditary metabolic diseases. Medium chain acyl-CoA dehydrogenase deficiency (MCADD) is among these diseases. We sought to evaluate the cost-effectiveness of introducing MCADD screening in France.

METHODS

We developed a decision model to evaluate, from a societal perspective and a lifetime horizon, the cost-effectiveness of expanding the French newborn screening programme to include MCADD. Published and, where available, routine data sources were used. Both costs and health consequences were discounted at an annual rate of 4%. The model was applied to a French birth cohort. One-way sensitivity analyses and worst-case scenario simulation were performed.

RESULTS

We estimate that MCADD newborn screening in France would prevent each year five deaths and the occurrence of neurological sequelae in two children under 5 years, resulting in a gain of 128 life years or 138 quality-adjusted life years (QALY). The incremental cost per year is estimated at €2.5 million, down to €1 million if this expansion is combined with a replacement of the technology currently used for phenylketonuria screening by MS/MS. The resulting incremental cost-effectiveness ratio (ICER) is estimated at €7 580/QALY. Sensitivity analyses indicate that while the results are robust to variations in the parameters, the model is most sensitive to the cost of neurological sequelae, MCADD prevalence, screening effectiveness and screening test cost. The worst-case scenario suggests an ICER of €72 000/QALY gained.

CONCLUSIONS

Although France has not defined any threshold for judging whether the implementation of a health intervention is an efficient allocation of public resources, we conclude that the expansion of the French newborn screening programme to MCADD would appear to be cost-effective. The results of this analysis have been used to produce recommendations for the introduction of universal newborn screening for MCADD in France.

Decision analysis, economic evaluation, and newborn screening: challenges and opportunities

The number of conditions included in newborn screening panels has increased rapidly in the United States during the past decade, and many more conditions are under consideration for addition to state panels. The rare nature of candidate conditions for newborn screening makes their evaluation challenging. The scarcity of data on the costs of screening, follow-up, treatment, and long-term disability must be addressed to improve the evaluation process for nominated conditions. Decision analyses and economic evaluations can help inform policy decisions for newborn screening programs by providing a systematic approach to synthesizing available evidence and providing projected estimates of long-term clinical and economic outcomes when long-term data are not available. In this review, we outline the types of data required for the development of decision analysis and cost-effectiveness models for newborn screening programs and discuss the challenges faced when applying these methods in the arena of newborn screening to help inform policy decisions.Genet Med advance online publication 5 April 2012.

Extended newborn screening: an update for the general paediatrician

Extended newborn screening (ENBS) with the use of tandem mass spectrometry technology is well established in all Australian states and in New Zealand. ENBS has afforded a marked reduction in morbidity and mortality in select conditions such as medium-chain acyl-CoA dehydrogenase deficiency. While this technology has been of great benefit to newborn screening, it comes with many inherent and unforeseen challenges. In this review, we discuss the successes and challenges associated with ENBS.

Newborn screening for medium chain acyl-CoA dehydrogenase deficiency in England: prevalence, predictive value and test validity based on 1.5 million screened babies

BACKGROUND

Medium chain acyl-CoA dehydrogenase deficiency (MCADD) is a rare, life-threatening condition. Early diagnosis by screening asymptomatic newborns may improve outcome, but the benefit to newborns identified with variants not encountered clinically is uncertain.

OBJECTIVE

To estimate, overall and by ethnic group: screen-positive prevalence and predictive value (PPV); MCADD prevalence; proportion MCADD variants detected of predicted definite or uncertain clinical importance.

SETTING

All births in areas of high ethnic minority prevalence in England.

METHODS

Prospective multicentre pilot screening service; testing at age five to eight days; standardized screening, diagnostic and management protocols; independent expert review of screen-positive cases to assign MCADD diagnosis and predicted clinical importance (definite or uncertain).

RESULTS

Approximately 1.5 million babies (79% white; 10% Asian) were screened. MCADD was confirmed in 147 of 190 babies with a positive screening result (screen-positive prevalence: 1.20 per 10,000; MCADD prevalence: 0.94 per 10,000; PPV 77% [95% CI 71-83]), comprising 103 (70%) with MCADD variants of definite clinical importance (95 white [95%]; 2 Asian [2%]) and 44 (30%) with variants of uncertain clinical importance (29 white [67%]; 12 Asian [28%]).

CONCLUSION

One baby in every 10,000 born in England is diagnosed with MCADD by newborn screening; around 60 babies each year. While the majority of MCADD variants detected are predicted to be of definite clinical importance, this varies according to ethnic group, with variants of uncertain importance most commonly found in Asian babies. These findings provide support for MCADD screening but highlight the need to take account of the ethnic diversity of the population tested at implementation.

[Infant coma in the emergency department: 2 cases of MCAD deficiency]

Medium-chain Acyl-CoA dehydrogenase deficiency (MCAD) is one of the most common fatty acid oxidation disorders. Clinical manifestations can be serious and lead to death if unrecognized. They are not specific and can mimic meningitis or an acute intestinal intussusception in its neurological form. Early recognition of MCAD and presymptomatic treatment of intercurrent illness improve the prognosis over the short- and long-term. MCAD deficiency satisfies the major criteria for newborn screening. We report the cases of 2 patients whose presentation was typical and severe. Early diagnosis of MCAD deficiency helped to start a simple treatment in both patients aimed at preventing further decompensation.

Incidence and patterns of inborn errors of metabolism in the Eastern Province of Saudi Arabia, 1983-2008

BACKGROUND AND OBJECTIVES

Individual inborn errors of metabolism (IEM) are rare disorders, but may not be that uncommon in our patient population. We report the incidence of IEM in a defined cohort of births at the Saudi Aramco medical facilities in the Eastern Province of Saudi Arabia over 25 years.

METHODS

The records of all patients diagnosed with IEM from 1 January 1983 to 31 December 2008 were reviewed and categorized according to accumulated or deficient metabolites into small-molecule disorders (aminoacidemia, organic acidopathies [OA], urea cycle defects, fatty acid oxidation, and carbohydrate metabolic disorders) and other disorders, including glycogen and lysosomal storage disorders (LSDs), and organelle disorders.

RESULTS

During the study period, 165,530 Saudi Arabian infants were born at Saudi Aramco and 248 were diagnosed with an IEM, corresponding to a cumulative incidence of 150 cases per 100,000 live births. Small-molecule disorders were diagnosed in 134/248 patients (54%). OA were the most common (48/248 patients; 19%), and methylmalonic aciduria was the most frequently observed OA (13/48 patients; 27%). LSDs were diagnosed in 74/248 patients (30%), and mucopolysaccharidosis was the most frequently observed LSD (28/74; 38%).

CONCLUSION

We believe that our data underestimate the true incidence of IEM in the region. Regional and national newborn screening programs will provide a better estimation of the incidence of IEM. We recommend a centralized newborn screening program that employs tandem mass spectrometry.

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.

A novel molecular aspect of Japanese patients with medium-chain acyl-CoA dehydrogenase deficiency (MCADD): c.449-452delCTGA is a common mutation in Japanese patients with MCADD

We studied 11 Japanese patients with medium-chain acyl-CoA dehydrogenase deficiency (MCADD) and found a common mutation, c.449-452delCTGA, which accounted for 45% of the mutations. Seven of 10 independent patients carried at least one copy of this mutation. Phenotypes of homozygous patients with the c.449-452delCTGA mutation varied from asymptomatic to life-threatening metabolic decompensation in Japanese patients with MCADD, similar to the phenotypic variations in Caucasians. This study suggests the genotypic difference between those of Caucasians and Japanese regarding MCADD.

Newborn screening for MCAD deficiency: experience of the first three years in British Columbia, Canada

BACKGROUND

Medium Chain Acyl-CoA Dehydrogenase (MCAD) Deficiency is an autosomal recessive disorder of fatty acid oxidation, with potential fatal outcome. MCAD deficiency is diagnosed by acylcarnitine analysis on newborn screening blood spot cards by tandem mass spectrometry. Early diagnosis of MCAD and presymptomatic treatment can potentially reduce morbidity and mortality.

OBJECTIVES

To evaluate incidence, clinical outcome, biochemical and molecular phenotype of MCAD cases detected in the first three years of newborn screening in British Columbia (BC).

METHODS AND RESULTS

Medium chain length acylcarnitines, octanoylcarnitine (C8) and decanoylcarnitine (C10), were measured on newborn screening blood spot cards. Out of 121,000 live births, 17 newborns had C8 values above the screening cut-off of 0.38 umol/L. Ten newborns had elevated C8 on repeat cards and were investigated further. Both C8 and C8/C10 ratios remained abnormal in all confirmed MCAD cases. Positive predictive value of screening was 58% with no false negative results. Seven patients were homozygous for the common c.985A > G MCAD mutation and three others were compound heterozygous for the c.985A > G and a second mutation. Two novel mutations were identified (c.260T > C and c.382T > A). The estimated incidence of MCAD was approximately 1:12,000 live births. Upon frequent feeding and carnitine supplementation, none of the patients had metabolic crises or adverse outcomes.

CONCLUSION

Frequency of MCAD in BC is comparable to reports from other newborn screening programs. Persistence of elevated C8 levels and C8/C10 ratios in confirmed MCAD cases suggest that these are sensitive markers for newborn screening. Early detection and treatment have successfully prevented adverse health outcomes in patients with MCAD.

Novel mutations causing medium chain acyl-CoA dehydrogenase deficiency: under-representation of the common c.985 A > G mutation in the New York state population

Medium chain acyl-CoA dehydrogenase deficiency (MCADD) is one of the most common fatty acid oxidation disorders. A subpopulation of children with MCADD present with metabolic crisis induced by fasting or illness, become lethargic, and can experience seizures or coma, culminating in a 20% mortality rate during the first episode. The frequency of these metabolic crises can be reduced with early diagnosis and treatment. The prevalence of MCADD in the United States is estimated to be 1 per 15,000 with p.K304E (c.985A > G) accounting for 90% of mutant alleles. In an 18-month period after initiating screening, the New York State Newborn Screening Mass Spectrometry Laboratory screened 385,893 newborns and referred 511 samples with elevated (>or=0.3 micromol/L) octanoylcarnitine (C8) levels for molecular testing. Of these referrals, six p.K304E homozygotes and 154 heterozygotes were identified. Twenty infants were biochemically confirmed with MCADD, per report from the child's pediatrician and/or treatment center. In these 20 cases, p.K304E accounted for only 47.5% of the mutant alleles. Further testing showed a second variant, p.Y42H, accounted for 7.5% of mutant alleles while the remaining 45% were unknown. Samples from all diagnosed non-p.K304E homozygous infants, and samples with C8 levels >or=1.0 micromol/L were sequenced (n = 16). Six novel and seven previously reported mutations were detected. These results suggest that p.K304E has a far lower representation in New York newborns with MCADD than current literature estimates and its full mutational spectrum is still unknown.

A Fatal Neonatal Presentation of Medium-chain Acyl Coenzyme a Dehydrogenase Deficiency

Medium-chain acyl coenzyme A dehydrogenase (MCAD) deficiency is the most common of the inborn errors of mitochondrial fatty acid β-oxidation. A male infant was born at 39 weeks of gestation following an uneventful pregnancy. He was discharged at age 28 h after a normal first-day check, but was subsequently re-admitted and died aged 44 h. Post-mortem blood and bile spot carnitine analysis revealed a profile consistent with MCAD deficiency. MCAD genotyping revealed 985 A to G (K329E) homozygosity. This is the first confirmed case of neonatal death due to MCAD deficiency in the UK.

Spectrum of medium-chain acyl-CoA dehydrogenase deficiency detected by newborn screening

OBJECTIVE

Our goal was to describe the clinical spectrum of medium-chain acyl-CoA dehydrogenase deficiency detected by routine newborn screening and assess factors associated with elevations of octanoylcarnitine in newborns and characteristics associated with adverse clinical consequences of medium-chain acyl-CoA dehydrogenase deficiency.

METHODS

The first 47 medium-chain acyl-CoA dehydrogenase deficiency cases detected by the New England Newborn Screening Program were classified according to initial and follow-up octanoylcarnitine values, octanoylcarnitine-decanoylcarnitine ratios, medium-chain acyl-CoA dehydrogenase genotype, follow-up biochemical parameters, and feeding by breast milk or formula.

RESULTS

All 20 patients who were homozygous for 985A-->G had high initial octanoylcarnitine values (7.0-36.8 microM) and octanoylcarnitine-decanoylcarnitine ratios (7.0-14.5), whereas the 27 patients with 0 to 1 copy of 985A-->G exhibited a wide range of octanoylcarnitine values (0.5-28.6 microM) and octanoylcarnitine-decanoylcarnitine ratios (0.8-12.7). Initial newborn octanoylcarnitine values decreased by days 5 to 8, but the octanoylcarnitine-decanoylcarnitine ratio generally remained stable. Among 985A-->G homozygotes, breastfed newborns had higher initial octanoylcarnitine values than newborns who received formula. Adverse events occurred in 5 children, 4 985A-->G homozygotes and 1 compound heterozygote with a very high initial octanoylcarnitine: 2 survived severe neonatal hypoglycemia, 1 survived a severe hypoglycemic episode at 15 months of age, and 2 died as a result of medium-chain acyl-CoA dehydrogenase deficiency at ages 11 and 33 months.

CONCLUSION

Newborn screening for medium-chain acyl-CoA dehydrogenase deficiency has detected cases with a wide range of genotypes and biochemical abnormalities. Although most children do well, adverse outcomes have not been entirely avoided. Assessment of potential risk and determination of appropriate treatment remain a challenge.

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).

A new genetic disorder in mitochondrial fatty acid beta-oxidation: ACAD9 deficiency

The acyl-CoA dehydrogenases are a family of multimeric flavoenzymes that catalyze the alpha,beta -dehydrogenation of acyl-CoA esters in fatty acid beta -oxidation and amino acid catabolism. Genetic defects have been identified in most of the acyl-CoA dehydrogenases in humans. Acyl-CoA dehydrogenase 9 (ACAD9) is a recently identified acyl-CoA dehydrogenase that demonstrates maximum activity with unsaturated long-chain acyl-CoAs. We now report three cases of ACAD9 deficiency. Patient 1 was a 14-year-old, previously healthy boy who died of a Reye-like episode and cerebellar stroke triggered by a mild viral illness and ingestion of aspirin. Patient 2 was a 10-year-old girl who first presented at age 4 mo with recurrent episodes of acute liver dysfunction and hypoglycemia, with otherwise minor illnesses. Patient 3 was a 4.5-year-old girl who died of cardiomyopathy and whose sibling also died of cardiomyopathy at age 21 mo. Mild chronic neurologic dysfunction was reported in all three patients. Defects in ACAD9 mRNA were identified in the first two patients, and all patients manifested marked defects in ACAD9 protein. Despite a significant overlap of substrate specificity, it appears that ACAD9 and very-long-chain acyl-CoA dehydrogenase are unable to compensate for each other in patients with either deficiency. Studies of the tissue distribution and gene regulation of ACAD9 and very-long-chain acyl-CoA dehydrogenase identify the presence of two independently regulated functional pathways for long-chain fat metabolism, indicating that these two enzymes are likely to be involved in different physiological functions.

Assessment of the prevalence of the 985A>G MCAD mutation in the French-Canadian population using allele-specific PCR

Inherited deficiency of medium-chain acyl-CoA dehydrogenase (MCAD) is a severe, sometimes fatal disorder. A single mutation in the MCAD gene, 985A>G, is involved in approximately 90% of cases. To evaluate the relevance of implementing a systematic population-based screening program in the province of Quebec using a biochemical test, we measured the prevalence of this mutation in a set of anonymous newborn samples from the Quebec City area, a region where the majority of its inhabitants are French-Canadians. An allele-specific polymerase chain reaction assay was designed and used to detect the mutation in 7143 DNA samples obtained from consecutive anonymous newborns. Pools of eight DNA samples were genotyped in parallel for the same mutation to validate this pooling strategy. The allelic frequency of the MCAD 985A>G mutation was found to be 0.71% and the carrier frequency 1:71 (95% confidence interval 1:55 to 1:98). This estimate predicts a homozygous frequency of 1:19,837. Ninety-nine heterozygous carriers and one homozygous individual were identified out of 7143 samples. There was 100% concordance between the individual and pooled analyses, and the pooling strategy reduced the total genotyping costs by approximately 70%. The carrier frequency estimated for this population is similar to other northwestern European populations and would support implementation of systematic newborn screening (such as tandem mass spectrometry screening) for this disease. Pooling DNA samples followed by genotyping appears to be cost-effective for estimating prevalence of rare mutations.

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.

Clinical efficacy and cost-effectiveness of newborn screening for medium chain acyl–CoA dehydrogenase deficiency using tandem mass spectrometry

OBJECTIVE

To determine the clinical efficacy and cost-effectiveness of newborn screening for MCADD using tandem mass spectrometry (MS/MS) compared with clinical diagnosis within the Canadian context.

DESIGN AND METHODS

A systematic review of the clinical and economic literature was performed. For primary economic analysis, a decision-tree model was built based on the available information, the impact of newborn screening on the health care and the relevant Canadian data.

RESULTS

Twenty-one clinical and two economic studies met the selection criteria. Mean incidence of MCADD was approximately 1:16,000. Clinical sensitivity and specificity were 100% and 99.99%, respectively. Screening significantly lowered morbidity and mortality. Both economic studies showed that screening for MCADD using MS/MS was cost-effective if willingness-to-pay was US 50,000 dollars. Our primary economic analysis showed that screening was cost-effective based on the cost-effective threshold of C 20,000 dollars per QALY.

CONCLUSION

Screening consumes more resources than no screening but attains better health outcomes.

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.

State newborn screening in the tandem mass spectrometry era: more tests, more false-positive results

BACKGROUND

The advent of tandem mass spectrometry has made it possible to test newborns for multiple conditions efficiently. It is not known how state newborn screening programs have changed screening practices in response to this technology and how it affects the number of false-positive test results.

METHODS

We obtained data from the National Newborn Screening and Genetics Resource Center regarding the screening practices for each of the 50 states, to determine the number of mandated disorders added to state newborn screening panels between 1995 and 2005. Combining these data with reported specificities from the literature and the number of births in each state, we estimated the number of infants who would have received false-positive results through screening with tandem mass spectrometry in 2005.

RESULTS

The average state mandated screening for 5 disorders in 1995 (range: 0-8 disorders). Wyoming was the only state that decreased its panel size over the next decade. Kansas and Texas were the only states that did not add disorders to their panels between 1995 and 2005; the average state added 19. Iowa, Minnesota, Mississippi, South Dakota, and Tennessee each added > or = 40 disorders. Assuming that an individual test for a disorder had a specificity of 99.995%, we estimated that approximately 2575 infants would have received false-positive results through screening with tandem mass spectrometry in 2005. If specificity was assumed to be 99.9%, then the number increased to > 51000.

CONCLUSIONS

State newborn screening programs have expanded dramatically in the past decade. Because the benefit of such testing may be unclear in some cases and because the number of infants who may receive false-positive results and may be labeled falsely as having disease is potentially sizeable, a more cautious approach is needed.

Biochemical findings in common inborn errors of metabolism

The application of tandem mass spectrometry (MS/MS) to newborn screening has led to the detection of patients with a wider spectrum of inborn errors of metabolism. A definitive diagnosis can often be established early enough to start treatment before symptoms appear. Here, we review common biochemical findings in disorders caused by deficiency of 3-methylcrotonyl-CoA carboxylase, isobutyryl-CoA dehydrogenase, 2-methyl-3-hydroxybutyryl-CoA dehydrogenase, 3-ketothiolase, 2-methylbutyryl-CoA dehydrogenase, and medium chain acyl CoA dehydrogenase. The diagnosis of these disorders requires biochemical confirmation by measurement of plasma acylcarnitine profile, urine organic acids, and urine acylglycine profiles followed by measurement of enzyme activity or detection of causative mutations. Early treatment can improve the outcome of these disorders.

Population spectrum of ACADM genotypes correlated to biochemical phenotypes in newborn screening for medium-chain acyl-CoA dehydrogenase deficiency

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most frequent inherited defect of fatty acid oxidation, with a significant morbidity and mortality in undiagnosed patients. Adverse outcomes can effectively be prevented by avoiding metabolic stress and following simple dietary measures. Therefore, prospective newborn screening (NBS) is being proposed for this condition. However, technical validation of MCADD population screening and assessment of its overall benefit require broadening of the as-yet-scarce knowledge of the MCADD genetic heterogeneity unraveled by NBS and its phenotypic consequences. Here, we describe the entire spectrum of sequence variations occurring in newborns with MCADD in the population of Bavaria, Germany, in relation to the biochemical phenotype. Among 524,287 newborns, we identified 62 cases of MCADD, indicating a birth incidence of 1 in 8,456. In all of the 57 newborns available for analysis, two alterations within the MCADD gene (ACADM) were identified. The most prevalent alteration c.985A>G (Lys329Glu) occurred in 27 (47%) newborns in the homozygous and in 18 (32%) in the heterozygous state (63% of defective alleles). The mild folding variant c.199T>C (Tyr67His) was identified in nine individuals, six of them being compound heterozygous with c.985A>G (Lys329Glu). Neither of the prevalent alterations were found in the remaining nine newborns. A total of 18 sequence variations were identified; 13 of them were novel: eight missense mutations, one nonsense mutation, two splice variants, and two small deletions. The remaining five were previously reported in MCADD patients. The ACADM heterogeneity uncovered was larger as anticipated from previous c.985A>G (Lys329Glu) carrier screening data. In addition, we show that MCADD appears to occur as frequently in Turkish newborns as in the native German population. Our data validate that biochemical NBS for MCADD is a highly specific procedure for disease detection, with the identification of a significant share of milder biochemical phenotypes, such as c.199T>C (Tyr67His). These show statistically lower acylcarnitine markers, allowing us to distinguish subgroups within the spectrum of ACADM sequence variations that correlate to biochemical MCADD disease expression. Our data might provide technical and medical guidance for decision making in the worldwide efforts to introduce MCADD population screening.

Newborn screening: complexities in universal genetic testing

Newborn screening (NBS)--in which each newborn infant is screened for up to 50 specific metabolic disorders for early detection and intervention--is the first program of populationwide genetic testing. As a public health intervention, NBS has greatly improved the lives of thousands of affected children. New technologies and new economic and social forces pose significant ethical and clinical challenges to NBS. Two primary challenges concern (1) accommodating clinical and ethical standards to rapid technological developments in NBS and (2) preparing public health systems to respond to the medical advances and social forces driving expansion of NBS programs. We describe and analyze these challenges through consideration of 3 disorders: phenylketonuria, medium-chain acyl-CoA dehydrogenase deficiency, and cystic fibrosis.

Medium-chain acyl-CoA dehydrogenase deficiency: genotype-biochemical phenotype correlations

The fatty acid oxidation disorder most commonly identified by tandem mass spectrometry newborn screening is the potentially fatal medium-chain acyl-CoA dehydrogenase deficiency (MCAD). In clinically presenting cases, 80% are homozygous for the common mutation, c.985A > G and 18% heterozygous. We screened 592,785 babies and identified 34 with MCAD, 17 homozygous for c.985A > G, 14 with one copy, and 3 with no copy. We sequenced the exons of 19 patients, the 17 carrying one or no copy of c.985A > G, and two with marginal findings, and examined correlations between groups of mutations and biochemical markers. We found two known or putative pathogenic mutations in 18 of the 19 patients. Two mutations appeared more than once: c.199T > C, not recorded in clinically presenting cases (n = 4), and c.583G > A (n = 2). Patients homozygous for c.985A > G had the highest levels of neonatal octanoylcarnitine, plasma octanoylcarnitine when asymptomatic, and urinary acylglycines. Compound heterozygotes of c.985A > G and other mutations had intermediate levels, and those without c.985A > G, or heterozygous for that and c.199T > C had the lowest levels of these analytes. There was overlap in all values. The c.985A > G and c.583G > A mutations appear to have functional effects towards the severe end of the spectrum, and the c.199T > C mutation a smaller effect, as has been previously postulated. If these results are confirmed and extended, this could influence the advice given to parents of babies with MCAD detected by newborn screening, and make management more specific. In the meantime, all MCAD patients identified by newborn screening have, by definition, a functional defect and require careful clinical management.

The clinical aspects of newborn screening: Importance of newborn screening follow-up

The aim of newborn screening is to identify presymptomatic healthy infants that will develop significant metabolic or endocrine derangements if left undiagnosed and untreated. The goal of ultimately reducing or eliminating irreversible sequelae is reached by maximizing test sensitivity of the primary newborn screening that measures specific analytes by a number of methodologies. Differentiation of true from false negatives is accomplished by the test specificity. This review discusses disorders for which, in general, there are available therapies and that are detected by routine and expanded newborn screening. Recommendations are presented for evaluation by a primary care physician, with confirmation by a metabolic or endocrinology specialist. Disorders are organized in tabular format by class of pathway or analyte, with attention to typical clinical presentations, confirmatory biochemical and molecular tests, and therapies. There are numerous challenges in clinical follow-up, including diagnosis and appropriate understanding of the consequences of the disorders. The data required to meet these challenges can be acquired only by large scale longitudinal comprehensive studies of outcome in children identified by newborn screening. Only with such data can newborn screening fully serve families.

Expanding screening for rare metabolic disease in the newborn: an analysis of costs, effect and ethical consequences for decision-making in Finland

AIM

Currently, the only metabolic disorder that newborns are screened for in Finland is congenital hypothyroidism. A proposal to start a pilot study on screening for other rare metabolic diseases using tandem mass spectrometry prompted a health technology assessment project on the effect and costs of expanded newborn screening programme options.

METHOD

A modelling study using data from current published studies, healthcare registers and expert opinion.

RESULTS

The annual running cost of screening 56,000 newborns for the chosen five disorders (congenital adrenal hyperplasia, medium-chain acyl-CoA dehydrogenase deficiency [MCADD], long chain 3-hydroxyacyl-CoA dehydrogenase deficiency [LCHADD], phenylketonuria [PKU] and glutaric aciduria type 1 [GA 1]) was estimated to be euros 2.5 million or euros 45 per newborn when starting costs were included. The costs per quality-adjusted life year (QALY) gained are a maximum of euros 25,500. Prevention of severe handicap in one newborn would reduce the costs to a maximum of euros 18,000 per QALY gained.

CONCLUSIONS

Expanding the Finnish neonatal screening programme would require a new organization. The cost-effectiveness, resources, ethics and equity need to be considered when deciding in favour of or against starting a new screening programme.

Newborn screening and the pediatric practitioner

Since the beginning of newborn screening for metabolic and other disorders in 1964, advances in the understanding of the disorders identified and development of new methods of testing newborn screening blood spots have contributed to improved health in children. Pediatricians and others involved in the health care of infants must be able to participate in the assessment and confirmatory testing of infants who have an abnormal test result and in the care of infants identified with a disorder. Expansion in the technology and number of disorders identified has complicated this process. As more and a greater variety of disorders are tested for and identified, a crucial collaborative role has emerged for the newborn screening programs and their public health professionals, the tertiary care specialists in the disorders and the primary care clinicians who comprise the medical home of the infants identified. This collaboration needs to provide prompt results of the newborn screening tests, expeditious and expert confirmatory testing and an effective care plan for the affected infant to realize the benefits of treatment for children with otherwise devastating disorders.

Fetal fatty acid oxidation disorders, their effect on maternal health and neonatal outcome: impact of expanded newborn screening on their diagnosis and management

Mitochondrial fatty acid oxidation disorders (FAOD) are recessively inherited errors of metabolism. Newborns with FAOD typically present with hypoketotic hypoglycemia, metabolic acidosis, hepatic failure, and cardiomyopathy. Late presentations include episodic myopathy, neuropathy, retinopathy, and arrhythmias. Sudden unexpected death can occur at any age and can be confused with sudden infant death syndrome. Some FAOD are associated with intrauterine growth restriction, prematurity, and pregnancy complications in the heterozygous mother, such as severe preeclampsia, acute fatty liver of pregnancy (AFLP), or hemolysis, elevated liver enzymes, and low platelets (HELLP) syndrome. Maternal pregnancy complications occur primarily in mothers carrying a fetus with long-chain l-3-hydroxyacyl CoA dehydrogenase deficiency or general trifunctional protein deficiencies. FAOD as a group represent the most common inborn errors of metabolism, and presymptomatic diagnosis of FAOD is the key to reduce morbidity and avoid mortality. The application of tandem mass spectrometry to newborn screening provides an effective means to identify most FAOD patients presymptomatically. At the beginning of 2005, 36 state newborn screening programs have mandated or adopted this technology resulting in a marked increase in the number of asymptomatic neonates with FAOD diagnosed. To ensure the long-term benefits of such screening programs, pediatricians and other health care providers must be educated about these disorders and their treatment.

Infusionstherapie und Ernährung von Risikogruppen

Besondere Situationen erfordern ein besonderes Vorgehen. Während bisher das »Standardvorgehen« bezüglich der Ernährung von pädiatrischen Patienten dargestellt wurde, beschäftigt sich das vorliegende Kapitel mit »Sondersituationen« der pädiatrischen Infusionstherapie und Ernährung. Behandlungssituationen, die ein besonderes Vorgehen bei der Therapie oder spezielle Aufmerksamkeit bei der Anpassung der Ernährung erfordern, entstehen in der Regel durch 4 mögliche Situationen:

spezifische Physiologie von Patientengruppen (z. B. Früh- oder Neugeborene),

Auswirkungen von therapeutischen Maßnahmen (z. B. Operationen),

Pathophysiologie von Erkrankungen (z. B. angeborene Stoffwechselerkrankungen, Erkrankungen des onkologischen, rheumatischen oder atopischen Formenkreises, Anorexia nervosa, Bulimie oder Adipositas) oder

besondere körperliche Belastungen [z. B. (Leistungs-)Sport].

Bekannte Strategien werden systematisch und prägnant dargestellt und diskutiert.

Die Beschäftigung mit der Ernährung von »Risikogruppen« übt das Erkennen und den Umgang von potenziellen Gefahrensituationen bei der Verordnung von bilanzierter Ernährung. So sollte auch derjenige von dem Kapitel profitieren, der sich mit den behandelten Patientengruppen, Situationen, Erkrankungen üblicherweise nicht beschäftigen muss.

Disclosing to parents newborn carrier status identified by routine blood spot screening

BACKGROUND

Newborn blood spot screening programmes are designed to detect serious conditions affecting individuals, where early treatment can improve health. It is suggested that screening can improve the experience of diagnosis for parents. For example, without newborn screening, when a child with cystic fibrosis becomes symptomatic a period of uncertainty can arise prior to diagnosis. These potential advantages of screening need to be weighed against potential disadvantages of screening at individual and population levels. Some newborn screening programmes inadvertently identify newborn infants who, although not affected by the condition, carry a gene for it and can pass on that gene to their children; these are 'genetic carriers'. Knowledge of newborn carrier status can lead to: testing of parents and family members, and concern about possible affected future siblings should both parents be identified as carriers; the possibility of such testing revealing the putative father is not the biological father; concern about the child's future reproductive choices; and unjustified anxiety about the health of the carrier newborn. There is an urgent need to develop clear guidance as to how to respond, with advances in technology fuelling the expansion of newborn blood spot screening and raised expectations of informed consent and disclosing test results. Depending on the condition for which screening is offered, options include: employing tests that do not identify carrier status, if available; identifying acceptable ways of disclosing carrier status; or identifying acceptable ways of not disclosing carrier status. These options are illustrated by screening programmes for sickle cell disorders and cystic fibrosis. Currently, there are no screening tests available for sickle cell disorders that do not identify carrier status. For cystic fibrosis, the policy choice is between an extended period of testing, and a screening result that is available sooner for most newborns, but inadvertently identifies carrier babies.

OBJECTIVES

The aim of this review was to assess the impact of disclosing to parents newborn carrier status inadvertently identified by routine newborn blood spot screening.

SEARCH STRATEGY

We searched for reports addressing disclosing newborn carrier status to parents following newborn screening for sickle cell disorders and cystic fibrosis in: commercially available electronic databases (October 2002), specialist registers, online journals, online abstracts and conference abstracts. We also scanned the reference lists of included papers.

SELECTION CRITERIA

Studies addressing the impact of disclosing carrier status using a soundly controlled trial or randomised controlled trial.

DATA COLLECTION AND ANALYSIS

Two researchers independently scanned titles and abstracts for relevance using the pre-specified inclusion criteria. Full reports of selected citations were then located and screened again for relevance by two researchers independently. At each stage, results were compared and discrepancies resolved by discussion.

MAIN RESULTS

We found no controlled trials about disclosing carrier status.

REVIEWERS' CONCLUSIONS

There is a need to develop and evaluate the effects of interventions to support the disclosure of carrier status to parents following newborn screening.

Rapid, comprehensive screening of the human medium chain acyl-CoA dehydrogenase gene

Newborn screening by tandem mass spectrometry (MS/MS) identifies patients with medium chain acyl-CoA dehydrogenase (MCAD) deficiency the most frequently observed disorder of fatty acid oxidation. Molecular genetic analysis is becoming a common tool to confirm those identified as affected by prospective screening and for carrier detection in family studies. The A985G (K304E) mutation accounts for approximately 80% of mutant alleles in MCAD deficient patients, presenting symptomatically, while greater variability of mutant alleles is observed among cases identified through prospective screening. Aside from A985G, the mutation spectrum in MCAD deficient patients is heterogeneous such that comprehensive gene analysis is required. Traditionally the MCAD gene is assayed by sequencing the entire coding region. Although effective and definitive, this approach is expensive, turn around time is slow, and is poorly amenable to a clinical service molecular genetics laboratory. Dye-binding/high-resolution thermal denaturation is a rapid and homogeneous method by which to scan a PCR product for evidence of sequence aberration. PCR is performed in capillaries in the presence of the dsDNA-binding dye LCGreen I and subsequently the DNA/dye complexes are analyzed by high-resolution thermal denaturation. DNA sequencing was limited to fragments displaying abnormal melting profiles. Of 18 specimens analyzed, 11 have a genotype consistent with MCAD deficiency and seven have a genotype consistent with carrier status. Clinical and biochemical data corroborate that the genotype results identified the affected patients and differentiates them from carriers. The entire process is homogeneous requiring no post-PCR manipulation and is completed in under 3 h.

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.

Data required for the evaluation of newborn screening programmes

Tandem mass spectrometry offers the chance to improve newborn screening (NBS) for phenylketonuria and to expand screening programmes at minimal additional costs. So far, however, there are only limited data available on the incidence of a broader range of disorders presently being considered, their natural course, the benefits achievable and potential harm associated with screening. Based on a literature search and experience from the Bavarian extended screening trial, these questions are addressed using medium-chain acyl-CoA dehydrogenase deficiency (MCADD) as an example. The data retrieved are sufficient for estimation of the incidence of MCADD cases identifiable by NBS and for diagnosis following clinical symptoms. Clinically detected cases ascertained by active surveillance in populations with highly developed and freely accessible health care systems consistently amount to only 33% of those identified by NBS. This difference cannot be explained by the difference in the proportion of the homozygous 985A-->G mutation, which accounts for about 50% of cases identified in NBS. Further research is needed to assess the contribution of MCADD to unexplained deaths in infancy. Retrospective cohort studies enrolling at least 500,000 children would allow for a more precise estimate of the natural course of disease in particular with regard to less severe adverse outcomes. The most relevant gap in knowledge concerns the long-term outcome of children identified following symptoms and by newborn screening. Since randomised controlled trials are unlikely to be feasible on this issue, a standardised documentation protocol should be implemented in follow-up studies for cases identified either by high risk screening or newborn screening. A proposal for the content of such observational studies is made.

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.

Arguments for early screening: a clinician's perspective

Recent technological advances have led to an expansion in inborn errors that can be detected in the newborn period. Further developments in newborn screening will increase this number further. There are two main arguments put forward to support the developments of an expanded newborn screening programme. Firstly there may be an improvement in patient outcome. The early detection of disorders either in the pre-symptomatic or early symptomatic phase should, with treatment, result in the prevention of severe illness. This is evident for phenylketonuria and generally accepted for homocystinuria and medium-chain acyl-CoA dehydrogenase deficiency, disorders which have a long pre-symptomatic phase. However, other inborn errors may present within the first 10 days of life with severe illness, particularly neonatal encephalopathy. In order to effectively stop the rapid progression of these disorders, screening must be undertaken early although where severe metabolic decompensation occurs within 2 to 3 days of birth, newborn screening programmes are unlikely to be of direct benefit. Secondly an early diagnosis, even when this does not affect that individual's prognosis, may allow for accurate genetic advise to be given to the family and the opportunity to have prenatal diagnosis for future pregnancies.

CONCLUSION

For the clinician, the introduction of an expanded and early newborn screening presents opportunities for improved patient and family care. However, it is important to be aware of possible detrimental effects on families of early screening. Screening tests must have adequate sensitivity and high specificity. Furthermore with early screening, close liaison between the laboratory, clinicians and community services is essential.

Ethical issues in newborn screening and the impact of new technologies

Medical ethics is an integral part of medical practice. The general principles are well known: autonomy (the right to choose), beneficence (do good), non-maleficence (do no harm), and justice (be fair and equitable). In newborn screening these principles must be especially carefully applied, as the intervention, screening, has not been sought by the patient, but is a form of preventive medicine. In proposing a screening programme questions to be asked are: should we do it? (is there enough benefit, not too much harm?); can we do it? (do we have the technology and skill to find the cases sought); can we afford it? The first question, with its ethical implications, is often ignored. New issues have arisen with new technology, but underlying ethical themes are the same. Tandem mass spectrometry can be used to detect about 30 very rare disorders in a single test. Proving the benefit of this (and other screening tests) is difficult because randomised controlled trials seem impractical, because of power considerations, long follow-up time, and because there is already a perceived benefit. Best possible evidence of a lower order must be sought. In future, DNA microarray technology is likely to become sufficiently inexpensive to apply to newborn screening. It is difficult to predict all the future possibilities of DNA technology in this fast-moving field. Major ethical problems are likely with the ability to detect adult-onset disorders or susceptibility to these in babies. Under what circumstances would this be ethical? We need to start debating these issues.

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.

Adult presentation of MCAD deficiency revealed by coma and severe arrythmias

We report the case of a 33-year-old man who presented with headaches and vomiting. Soon after admission he became drowsy and agitated, developed ventricular tachycardia and his neurological state worsened (Glasgow coma score 6). Blood analysis showed respiratory alkalosis, hyperlactacidemia (8 mmol/l), hyperammonemia (390 micro mol/l) and hypoglycaemia (2.4 mmol/l). Subsequently, he developed supraventricular tachycardia, ventricular tachycardia and ultimately ventricular fibrillation resulting in cardiac arrest, which was successfully treated. A CT scan of the head revealed cerebral oedema. Whilst in the intensive care unit, he developed renal failure and rhabdomyolysis. The metabolic abnormalities seen at the time of admission normalised within 48 h with IV glucose infusion. Biological investigations, including urinary organic acids and plasma acylcarnitines, showed results compatible with MCAD deficiency. Mutation analysis revealed the patient was homozygous for the classical mutation A985G. This is one of only a few reports of severe cardiac arrhythmia in an adult due to MCAD deficiency. This condition is probably under-diagnosed in adult patients with acute neurological and/or cardiac presentations.

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.

Screening newborns for inborn errors of metabolism by tandem mass spectrometry

BACKGROUND

The recent development of electrospray tandem mass spectrometry makes it possible to screen newborns for many rare inborn errors of metabolism, but the efficacy and outcomes of screening remain unknown. We examined the effect of the screening of newborns by tandem mass spectrometry on the rates of diagnosis of 31 disorders.

METHODS

We compared the rates of detection of 31 inborn errors affecting the metabolism of the urea cycle, amino acids, and organic acids and fatty-acid oxidation among 362,000 newborns screened by tandem mass spectrometry over a four-year period (April 1998 through March 2002) with the rates in six preceding four-year birth cohorts in New South Wales and the Australian Capital Territory, Australia, where screening, diagnostic, and clinical services were centralized.

RESULTS

The overall prevalence of disorders during the periods when clinical diagnosis was used did not vary between 1982 and 1998. In the cohort screened with tandem mass spectrometry, the prevalence of inborn errors, excluding phenylketonuria, was 15.7 per 100,000 births (95 percent confidence interval, 11.9 to 20.4), as compared with adjusted rates of 8.6 to 9.5 per 100,000 births in the four preceding four-year cohorts. Of the 57 cases diagnosed after the introduction of newborn screening, 15 were diagnosed clinically; 7 of the 15 newborns had a normal result on screening. The rate of detection was increased specifically for medium-chain acyl-coenzyme A dehydrogenase deficiency (P<0.001) and other disorders of fatty-acid oxidation (P=0.007), as compared with the 16-year period before the implementation of neonatal screening for these disorders.

CONCLUSIONS

More cases of inborn errors of metabolism are diagnosed by screening with tandem mass spectrometry than are diagnosed clinically. It is not yet clear which patients with disorders diagnosed by such screening would have become symptomatic if screening had not been performed.