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).

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.

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.

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.

A cell-based time-resolved fluorescence assay for selection of antibody reagents for G protein-coupled receptor immunohistochemistry

A cell-based time-resolved fluorescence (celTRF) immunoassay is described for pre-screening antibodies to G protein-coupled receptor (GPCR) peptides that predicts suitability for immunohistochemistry (IHC). Rat GPCRs were expressed in Saos-2 human osteosarcoma cells via recombinant baculoviruses designed for mammalian cell expression, i.e., the transduced cells were used as a "screening lawn". The lawn was fixed and permeabilized similarly to IHC tissue. The celTRF, a dissociation-enhanced lanthanide fluorescence immunoassay (DELFIA), employed Eu-labelled goat anti-rabbit IgG. It exhibited a broad dynamic range upon which enzyme-linked immunosorbant assay (ELISA)-positive affinity-purified anti-peptide antibody reagents were examined for specificity and potency. Over 150 anti-peptide reagents to 27 GPCRs were characterized. All celTRF-positive antibodies were found to be suitable for IHC, whereas ELISA alone did not predict IHC utility. Examples are illustrated with five rabbit anti-neuropeptide FF receptor 1 (NPFF1) antibodies, where a strong correlation between celTRF potency and IHC utility was observed in both applications. In contrast, two high anti-peptide ELISA titer but celTRF-negative antibodies failed to recognize the NPFF1 receptor in IHC. The celTRF assay was performed manually and in an automated fashion, in our case, using a Biomek FX station and Sami scheduling software. The celTRF is the first in vitro automated assay that offers confident pre-selection of antibodies for IHC and the versatility to accommodate the rapid screening of large numbers of GPCRs. The celTRF is readily applicable to other protein target classes.

Genetic screening of newborns

Screening of newborn infants for genetic disease began over 35 years ago as a public health measure to prevent mental retardation in phenylketonuria (PKU). It was so successful that tests for several other genetic disorders were added. We review the current status of this screening, including discussions of the genetic disorders often covered and the results of newborn screening for them. We emphasize recent advances. These include expansion of coverage for genetic disorders with the new methodology of tandem mass spectrometry (MS-MS) and the introduction of molecular (DNA) testing to increase the specificity of testing for several disorders, thereby reducing false-positive rates. These and other advances have also produced issues of criteria for screening, missed cases, and appropriate use of stored newborn specimens.

Population-based screening for rare mutations: high-throughput DNA extraction and molecular amplification from Guthrie cards

To determine the population-based frequency of a rare mutation (the 121ins2 mutation in the surfactant protein B gene), we developed high-throughput techniques to extract reliably and rapidly amplifiable DNA from Guthrie cards. Using a 3-mm punch from each of 10,044 Guthrie cards obtained from the Missouri Department of Health, we extracted DNA with deionized water by heating in the presence of 2% Chelex in a 96-well format. Average yield of DNA from each punch was 52.6 +/- 21 microg. Using 36mer primers and a 10-microL reaction volume, we amplified a 354-bp fragment of the surfactant protein B gene that contained the mutation and identified the mutation by its susceptibility to restriction enzyme digestion with SfuI. The procedure required 5 h per 96 samples but only 2 h of technician time. The amplification rate on the first attempt was 99.2%. Based on detection of eight individuals heterozygous for the mutation (confirmed by direct sequencing), we estimate the allele frequency to be 0.8/1000 individuals, an estimate not significantly different from previous estimates based on independent methods. High-throughput DNA extraction and amplification will permit establishment of DNA banks as well as efficient estimation of population-based genotype frequency for both rare and common genetic disorders.

A public health response to emerging technology: expansion of the Massachusetts newborn screening program

The development of a new technology, called tandem mass spectrometry (tandem MS), has challenged governments worldwide to consider expanding universal newborn screening for rare metabolic disorders. In 1997 the Massachusetts Department of Public Health developed a public process to meet this challenge. After addressing significant medical, legal, ethical, and logistical issues raised by tandem MS, Massachusetts incorporated one new disorder into the mandatory newborn screen and developed an optional pilot program for 20 additional disorders. The Massachusetts experience has wide relevance for other nations and states. As screening protocols are contemplated for entire populations-for newborns and others- it will remain essential that the public participate in an open process of reviewing the justification for and logistics of screening.

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.

Automated mutation analysis

Automated mutation analysis brings with it a vastly increased capacity in the number of test samples that can be processed at a time, as well as much improved test reproducibility. Until now, the introduction of automation into this field had been restricted to the use of semiautomated sequencing systems to make the most of the sequence information extractable from a single lane in an electrophoretic gel or in a polymer-filled glass capillary. Much effort is now being directed into harnessing the potential of DNA microarrays (DNA chips) and there is increasing interest in the potential of matrix-assisted mass spectrometry for determining the detail of large nucleic acid molecules. Meanwhile, there are other important recent developments already available, including robotic workstations, the further development of the allele-specific oligonucleotide assay into microtitre formats, and its use with fluorescence for real-time quantitative PCR analysis. Implementation of these developments in appropriate settings can further streamline the routine of molecular diagnostic laboratories, allowing them to take greater advantage of the recent surge of gene discoveries and their associated disease-causing mutations.

The frequency of an inactivating point mutation (566C-->T) of the human follicle-stimulating hormone receptor gene in four populations using allele-specific hybridization and time-resolved fluorometry

We have described previously in the Finnish population an inactivating point mutation (566C-->T) in the human FSH receptor (FSHR) gene. In women, this mutation causes hypergonadotropic ovarian failure with arrest of follicular maturation and infertility, whereas in men, there is variable suppression of spermatogenesis, but no absolute infertility. To determine whether the same FSHR mutation occurs in other populations, its frequency was determined in Finland, Switzerland, Denmark, and the Chinese population of Singapore. The mutation was screened for using genomic DNA extracted from whole blood or dried blood spots. Exon 7 of the FSHR gene was first amplified using a pair of biotinylated primers. The PCR products were then immobilized on streptavidin-coated microtitration wells and hybridized using short allele-specific oligonucleotide probes labeled with europium. Time-resolved fluorometry was used for europium signal detection. To test the reliability of this method, 40 isolated DNA samples and 35 dried blood spot samples were blindly tested for the 566C-->T FSHR mutation. The analyses yielded identical results with denaturing gradient gel electrophoresis and allele-specific restriction enzyme digestion of the same samples, thus demonstrating the reliability of the tested method. Automation of this procedure allows the screening of large numbers of samples, which was subsequently carried out to investigate the frequency of the 566C-->T mutation in the study populations. A total of 4981 samples from the above-mentioned 4 countries were analyzed. The frequency of the 566C-->T mutation was 0.96% for all Finnish samples (n=1976), with a strong enrichment of the mutant allele in the northeastern part of the country. Only 1 mutation carrier was identified in the samples from Switzerland (n=1162), whereas none was found in samples from Denmark (n=1094) and the Singapore Chinese (n=540). These results suggest that the 566C-->T mutation of the FSHR gene is enriched in Finland, but is uncommon in other populations.

Molecular diagnosis of medium-chain acyl-CoA dehydrogenase deficiency by oligonucleotide ligation assay

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is a recessively inherited defect in the mitochondrial β-oxidation of fatty acids. A single nucleotide change, the A985→G transition, in the MCAD gene accounts for ∼90% of all the disease-causing mutations in the patients. We have used PCR to amplify a segment of the human MCAD gene and typed the allelic sequence variation at base 985 by a colorimetric oligonucleotide ligation assay (OLA). PCR/OLA provides a technique that permits differentiation of the homozygotes, heterozygotes, and normals for the A985→G allele in the MCAD gene. Genotyping of 1908 random Finnish DNA samples by OLA identified 10 carriers of the mutant allele, but no homozygotes were found. The calculated carrier frequency for the A985→G mutation was 1:191 (95% confidence limits, 1:118–1:501), and the calculated frequency for the A985→G homozygotes was 1:147 000 (95% confidence limits, 1:56 000–1:1 004 000).