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The role of exome sequencing in newborn screening for inborn errors of metabolism.

ABSTRACT: Public health newborn screening (NBS) programs provide population-scale ascertainment of rare, treatable conditions that require urgent intervention. Tandem mass spectrometry (MS/MS) is currently used to screen newborns for a panel of rare inborn errors of metabolism (IEMs)^1-4. The NBSeq project evaluated whole-exome sequencing (WES) as an innovative methodology for NBS. We obtained archived residual dried blood spots and data for nearly all IEM cases from the 4.5 million infants born in California between mid-2005 and 2013 and from some infants who screened positive by MS/MS, but were unaffected upon follow-up testing. WES had an overall sensitivity of 88% and specificity of 98.4%, compared to 99.0% and 99.8%, respectively for MS/MS, although effectiveness varied among individual IEMs. Thus, WES alone was insufficiently sensitive or specific to be a primary screen for most NBS IEMs. However, as a secondary test for infants with abnormal MS/MS screens, WES could reduce false-positive results, facilitate timely case resolution and in some instances even suggest more appropriate or specific diagnosis than that initially obtained. This study represents the largest, to date, sequencing effort of an entire population of IEM-affected cases, allowing unbiased assessment of current capabilities of WES as a tool for population screening.

SUBMITTER: Adhikari AN

PROVIDER: S-EPMC8800147 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:Tandem mass spectrometry (MS MS) and simple fluorometric assays are currently used in newborn screening programs to detect inborn errors of metabolism (IEM). The aim of the study was to evaluate the clinical utility of exome sequencing as a second tier screening method to assist clinical diagnosis of the newborn. METHODS:A novel PCR-exome amplification and re-sequencing (PEARS) assay was designed and used to detect mutations in 122 genes associated with 101 IEM. Newborn bloodspots positive by biochemical testing were analysed by PEARS assay to detect pathogenic mutations relevant to the IEM. RESULTS:In initial validation studies of genomic DNA samples, PEARS assay correctly detected 25 known mutations associated with 17 different IEM. Retrospective gene analysis of newborns with clinical phenylketonuria (PKU), identified compound heterozygote phenylalanine hydroxylase (PAH) gene mutations in eight of nine samples (89%). Prospective analysis of 211 bloodspots correctly identified the two true PKU samples, yielding positive and negative predictive values of 100%. Testing of 8 true positive MS MS samples correctly identified potentially pathogenic compound heterozygote genotypes in 2 cases of citrullinemia type 1 and one case each of methylmalonic acidemia, isobutyryl-CoA dehydrogenase deficiency, short chain acyl-CoA dehydrogenase deficiency and glutaric acid type II and heterozygous genotypes in 2 cases of autosomal dominant methioninemia. Analysis of 11 of 12 false positive MS MS samples for other IEM identified heterozygous carriers in 8 cases for the relevant genes associated with the suspected IEM. In the remaining 3 cases, the test revealed compound heterozygote mutations in other metabolic genes not associated with the suspected IEM, indicating a misinterpretation of the original MS MS data. CONCLUSIONS:The PEARS assay has clinical utility as a rapid and cost effective second-tier test to assist the clinician to accurately diagnose newborns with a suspected IEM.

Project description:BackgroundThis study reports on the use of whole exome sequencing (WES) to diagnose children with inborn errors of metabolism and other disorders in United Arab Emirates.MethodsFrom January 2012 to December 2014, 85 patients (46 % females) were seen in the metabolic center at Tawam Hospital (Abu Dhabi) and WES testing was requested because definitive diagnoses were not reached by conventional methods.ResultsEighty (93 %) patients were <18 years old and 44 (52 %) were <5 years. Sixty-eight (80 %) patients had neurologic abnormalities. WES facilitated rapid diagnosis in 50 % of the patients, especially those with mitochondrial disorders. Yet, in most cases extensive investigation was required after the results were available. Most patients with confirmed molecular diagnoses had autosomal recessive disorders and were homozygous for the rare alleles. Most patients with autosomal dominant disorders and all patients with X-linked disorders had de novo mutations. WES results were negative (no pathogenic variants related to patient phenotype were identified) in six patients and incorrect in two patients. One patient had a reported "deleterious" hemizygous mutation in SLC35A2, c.617_620del (p.Q206fs), suggesting 'congenital disorder of glycosylation, TYPE IIm', but glycosylation studies were normal and healthy brothers had the same mutation. Another patient had "pathogenic" mutation in MCCC2, c.1015G > A (p.V339M), but urine organic acids was normal. WES confirmed inborn errors of metabolism (five mitochondrial diseases, three lysosomal storage diseases, and six other disorders) in 14 patients and genetic disorders (14 neurological diseases and three non-neurological diseases) in 17 patients. Variants of unknown significance were identified in 48 patients; 12 had "confirmed pathologic variants"and 12 had "likely pathologic variants", based on consistent phenotypes, biochemical/ segregation studies, or reported pathogenicity. In 24 patients, the variants were inconsistent with phenotypes or biochemical/ familial studies.ConclusionsAlthough WES provided molecular diagnoses, the results required careful interpretations and many patients required additional investigations. This tool is useful when conventional diagnostic methods fail. Staff competence in obtaining consent/ permission, interpreting the findings, and providing the proper counseling are essential before incorporating this technology into routine clinical practices.

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The role of exome sequencing in newborn screening for inborn errors of metabolism.

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