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Wojcik MH, Reuter CM, Marwaha S, Mahmoud M, Duyzend MH, Barseghyan H, Yuan B, Boone PM, Groopman EE, Délot EC, Jain D, Sanchis-Juan A, Starita LM, Talkowski M, Montgomery SB, Bamshad MJ, Chong JX, Wheeler MT, Berger SI, O’Donnell-Luria A, Sedlazeck FJ, Miller DE. Beyond the exome: what's next in diagnostic testing for Mendelian conditions. ARXIV 2023:arXiv:2301.07363v1. [PMID: 36713248 PMCID: PMC9882576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Despite advances in clinical genetic testing, including the introduction of exome sequencing (ES), more than 50% of individuals with a suspected Mendelian condition lack a precise molecular diagnosis. Clinical evaluation is increasingly undertaken by specialists outside of clinical genetics, often occurring in a tiered fashion and typically ending after ES. The current diagnostic rate reflects multiple factors, including technical limitations, incomplete understanding of variant pathogenicity, missing genotype-phenotype associations, complex gene-environment interactions, and reporting differences between clinical labs. Maintaining a clear understanding of the rapidly evolving landscape of diagnostic tests beyond ES, and their limitations, presents a challenge for non-genetics professionals. Newer tests, such as short-read genome or RNA sequencing, can be challenging to order and emerging technologies, such as optical genome mapping and long-read DNA or RNA sequencing, are not available clinically. Furthermore, there is no clear guidance on the next best steps after inconclusive evaluation. Here, we review why a clinical genetic evaluation may be negative, discuss questions to be asked in this setting, and provide a framework for further investigation, including the advantages and disadvantages of new approaches that are nascent in the clinical sphere. We present a guide for the next best steps after inconclusive molecular testing based upon phenotype and prior evaluation, including when to consider referral to a consortium such as GREGoR, which is focused on elucidating the underlying cause of rare unsolved genetic disorders.
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Affiliation(s)
- Monica H. Wojcik
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA 02142 USA
- Division of Genetics and Genomics, Boston Children’s Hospital, Harvard Medical School, Boston, MA 02115 USA
- Division of Newborn Medicine, Boston Children’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Chloe M. Reuter
- Department of Medicine, Division of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, CA 94305 USA
| | - Shruti Marwaha
- Department of Medicine, Division of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, CA 94305 USA
| | - Medhat Mahmoud
- Human Genome Sequencing Center, Baylor College of Medicine, One Baylor Plaza, Houston TX 77030 USA
| | - Michael H. Duyzend
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA 02142 USA
- Division of Genetics and Genomics, Boston Children’s Hospital, Harvard Medical School, Boston, MA 02115 USA
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114 USA
| | - Hayk Barseghyan
- Center for Genetics Medicine Research, Children’s National Research Institute, Children’s National Hospital, Washington, DC 20010 USA
- Department of Genomics and Precision Medicine, School of Medicine and Health Sciences, George Washington University, Washington, DC 20037 USA
| | - Bo Yuan
- Department of Molecular and Human Genetics and Human Genome Sequencing Center, Baylor College of Medicine, One Baylor Plaza, Houston TX 77030 USA
| | - Philip M. Boone
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA 02142 USA
- Division of Genetics and Genomics, Boston Children’s Hospital, Harvard Medical School, Boston, MA 02115 USA
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114 USA
| | - Emily E. Groopman
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA 02142 USA
- Division of Genetics and Genomics, Boston Children’s Hospital, Harvard Medical School, Boston, MA 02115 USA
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114 USA
| | - Emmanuèle C. Délot
- Department of Genomics and Precision Medicine, School of Medicine and Health Sciences, George Washington University, Washington, DC 20037 USA
- Center for Genetics Medicine Research, Children’s National Research and Innovation Campus, Washington, DC, USA
- Department of Pediatrics, George Washington University, School of Medicine and Health Sciences, George Washington University, Washington, DC 20037 USA
| | - Deepti Jain
- Department of Biostatistics, School of Public Health, University of Washington, Seattle WA 98195 USA
| | - Alba Sanchis-Juan
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA 02142 USA
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114 USA
| | | | - Lea M. Starita
- Brotman Baty Institute for Precision Medicine, University of Washington, Seattle, WA 98195 USA
- Department of Genome Sciences, University of Washington, Seattle, WA, 98195 USA
| | - Michael Talkowski
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA 02142 USA
- Center for Genomic Medicine, Massachusetts General Hospital, Boston, MA 02114 USA
- Department of Neurology, Massachusetts General Hospital and Harvard Medical School
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA
| | - Stephen B. Montgomery
- Department of Biomedical Data Science, Stanford University School of Medicine, Stanford, CA 94305 USA
- Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305 USA
- Department of Pathology, Stanford University School of Medicine, Stanford, CA 94305 USA
| | - Michael J. Bamshad
- Brotman Baty Institute for Precision Medicine, University of Washington, Seattle, WA 98195 USA
- Department of Genome Sciences, University of Washington, Seattle, WA, 98195 USA
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195 USA
| | - Jessica X. Chong
- Brotman Baty Institute for Precision Medicine, University of Washington, Seattle, WA 98195 USA
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195 USA
| | - Matthew T. Wheeler
- Department of Medicine, Division of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, CA 94305 USA
| | - Seth I. Berger
- Center for Genetics Medicine Research and Rare Disease Institute, Children’s National Hospital, Washington, DC 20010 USA
| | - Anne O’Donnell-Luria
- Program in Medical and Population Genetics, Broad Institute of MIT and Harvard, Cambridge, MA 02142 USA
- Division of Genetics and Genomics, Boston Children’s Hospital, Harvard Medical School, Boston, MA 02115 USA
- Center for Genomic Medicine, Analytic and Translational Genetics Unit, Massachusetts General Hospital, Boston, MA 02114 USA
| | - Fritz J. Sedlazeck
- Human Genome Sequencing Center, Baylor College of Medicine, One Baylor Plaza, Houston TX 77030 USA
- Department of Computer Science, Rice University, 6100 Main Street, Houston, TX, 77005 USA
| | - Danny E. Miller
- Brotman Baty Institute for Precision Medicine, University of Washington, Seattle, WA 98195 USA
- Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, WA 98195 USA
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, WA, 98195 USA
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Xu KK, Wegner DJ, Geurts LC, Heins HB, Yang P, Hamvas A, Eghtesady P, Sweet SC, Sessions Cole F, Wambach JA. Biologic characterization of ABCA3 variants in lung tissue from infants and children with ABCA3 deficiency. Pediatr Pulmonol 2022; 57:1325-1330. [PMID: 35170262 PMCID: PMC9148430 DOI: 10.1002/ppul.25862] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Revised: 12/31/2021] [Accepted: 01/24/2022] [Indexed: 11/10/2022]
Abstract
ABCA3 is a phospholipid transporter protein required for surfactant assembly in lamellar bodies of alveolar type II cells. Biallelic pathogenic ABCA3 variants cause severe neonatal respiratory distress syndrome or childhood interstitial lung disease. However, ABCA3 genotype alone does not explain the diversity in disease presentation, severity, and progression. Additionally, monoallelic ABCA3 variants have been reported in infants and children with ABCA3-deficient phenotypes. The effects of most ABCA3 variants identified in patients have not been characterized at the RNA level. ABCA3 allele-specific expression occurs in some cell types due to epigenetic regulation. We obtained lung tissue at transplant or autopsy from 16 infants and children with ABCA3 deficiency due to compound heterozygous ABCA3 variants for biologic characterization of the predicted effects of ABCA3 variants at the RNA level and determination of ABCA3 allele expression. We extracted DNA and RNA from frozen lung tissue and reverse-transcribed cDNA from mRNA. We performed Sanger sequencing to assess allele-specific expression by comparing the heights of variant nucleotide peaks in amplicons from genomic DNA and cDNA. We found similar genomic and cDNA variant nucleotide peak heights and no evidence of allele-specific expression among explant or autopsy samples with biallelic missense ABCA3 variants (n = 6). We observed allele-specific expression of missense alleles in trans with frameshift (n = 4) or nonsense (n = 1) variants, attributable to nonsense-mediated decay. The missense variant c.53 A > G;p.Gln18Arg, located near an exon-intron junction, encoded abnormal splicing with skipping of exon 4. Biologic characterization of ABCA3 variants can inform discovery of variant-specific disease mechanisms.
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Affiliation(s)
- Kathryn K Xu
- Edward Mallinckrodt Department of Pediatrics, Washington University in St. Louis School of Medicine and St. Louis Children's Hospital, St. Louis, Missouri, USA
| | - Daniel J Wegner
- Edward Mallinckrodt Department of Pediatrics, Washington University in St. Louis School of Medicine and St. Louis Children's Hospital, St. Louis, Missouri, USA
| | - Lucille C Geurts
- Edward Mallinckrodt Department of Pediatrics, Washington University in St. Louis School of Medicine and St. Louis Children's Hospital, St. Louis, Missouri, USA
| | - Hillary B Heins
- Edward Mallinckrodt Department of Pediatrics, Washington University in St. Louis School of Medicine and St. Louis Children's Hospital, St. Louis, Missouri, USA
| | - Ping Yang
- Edward Mallinckrodt Department of Pediatrics, Washington University in St. Louis School of Medicine and St. Louis Children's Hospital, St. Louis, Missouri, USA
| | - Aaron Hamvas
- Department of Pediatrics, Ann & Robert H. Lurie Children's Hospital of Chicago and Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
| | - Pirooz Eghtesady
- Department of Surgery, Washington University in St. Louis School of Medicine and St. Louis Children's Hospital, St. Louis, Missouri, USA
| | - Stuart C Sweet
- Edward Mallinckrodt Department of Pediatrics, Washington University in St. Louis School of Medicine and St. Louis Children's Hospital, St. Louis, Missouri, USA
| | - F Sessions Cole
- Edward Mallinckrodt Department of Pediatrics, Washington University in St. Louis School of Medicine and St. Louis Children's Hospital, St. Louis, Missouri, USA
| | - Jennifer A Wambach
- Edward Mallinckrodt Department of Pediatrics, Washington University in St. Louis School of Medicine and St. Louis Children's Hospital, St. Louis, Missouri, USA
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