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Downie L, Bouffler SE, Amor DJ, Christodoulou J, Yeung A, Horton AE, Macciocca I, Archibald AD, Wall M, Caruana J, Lunke S, Stark Z. Gene selection for genomic newborn screening: Moving toward consensus? Genet Med 2024; 26:101077. [PMID: 38275146 DOI: 10.1016/j.gim.2024.101077] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Revised: 01/15/2024] [Accepted: 01/18/2024] [Indexed: 01/27/2024] Open
Abstract
PURPOSE Gene selection for genomic newborn screening (gNBS) underpins the validity, acceptability, and ethical application of this technology. Existing gNBS gene lists are highly variable despite being based on shared principles of gene-disease validity, treatability, and age of onset. This study aimed to curate a gNBS gene list that builds upon existing efforts and provide a core consensus list of gene-disease pairs assessed by multiple expert groups worldwide. METHODS Our multidisciplinary expert team curated a gene list using an open platform and multiple existing curated resources. We included severe treatable disorders with age of disease onset <5 years with established gene-disease associations and reliable variant detection. We compared the final list with published lists from 5 other gNBS projects to determine consensus genes and to identify areas of discrepancy. RESULTS We reviewed 1279 genes and 604 met our inclusion criteria. Metabolic conditions comprised the largest group (25%), followed by immunodeficiencies (21%) and endocrine disorders (15%). We identified 55 consensus genes included by all 6 gNBS research projects. Common reasons for discrepancy included variable definitions of treatability and strength of gene-disease association. CONCLUSION We have identified a consensus gene list for gNBS that can be used as a basis for systematic harmonization efforts internationally.
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Affiliation(s)
- Lilian Downie
- Victorian Clinical Genetics Services, Murdoch Children's Research Institute, Melbourne, VIC, Australia; Murdoch Children's Research Institute, Melbourne, VIC, Australia; University of Melbourne, Melbourne, VIC, Australia
| | | | - David J Amor
- Murdoch Children's Research Institute, Melbourne, VIC, Australia; University of Melbourne, Melbourne, VIC, Australia
| | - John Christodoulou
- Victorian Clinical Genetics Services, Murdoch Children's Research Institute, Melbourne, VIC, Australia; Murdoch Children's Research Institute, Melbourne, VIC, Australia; University of Melbourne, Melbourne, VIC, Australia
| | - Alison Yeung
- Victorian Clinical Genetics Services, Murdoch Children's Research Institute, Melbourne, VIC, Australia; University of Melbourne, Melbourne, VIC, Australia
| | - Ari E Horton
- Victorian Heart Institute, Monash University, Melbourne, VIC, Australia; Public Health Genomics, School of Public Health and Preventive Medicine, Monash University, Melbourne, VIC, Australia
| | - Ivan Macciocca
- Victorian Clinical Genetics Services, Murdoch Children's Research Institute, Melbourne, VIC, Australia; University of Melbourne, Melbourne, VIC, Australia
| | - Alison D Archibald
- Victorian Clinical Genetics Services, Murdoch Children's Research Institute, Melbourne, VIC, Australia; Murdoch Children's Research Institute, Melbourne, VIC, Australia; University of Melbourne, Melbourne, VIC, Australia
| | - Meghan Wall
- Victorian Clinical Genetics Services, Murdoch Children's Research Institute, Melbourne, VIC, Australia; Murdoch Children's Research Institute, Melbourne, VIC, Australia; University of Melbourne, Melbourne, VIC, Australia
| | - Jade Caruana
- Murdoch Children's Research Institute, Melbourne, VIC, Australia
| | - Sebastian Lunke
- Victorian Clinical Genetics Services, Murdoch Children's Research Institute, Melbourne, VIC, Australia; University of Melbourne, Melbourne, VIC, Australia
| | - Zornitza Stark
- Victorian Clinical Genetics Services, Murdoch Children's Research Institute, Melbourne, VIC, Australia; University of Melbourne, Melbourne, VIC, Australia; Australian Genomics, Melbourne, VIC, Australia.
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Tang C, Li L, Chen T, Li Y, Zhu B, Zhang Y, Yin Y, Liu X, Huang C, Miao J, Zhu B, Wang X, Zou H, Han L, Feng J, Huang Y. Newborn Screening for Inborn Errors of Metabolism by Next-Generation Sequencing Combined with Tandem Mass Spectrometry. Int J Neonatal Screen 2024; 10:28. [PMID: 38651393 PMCID: PMC11036227 DOI: 10.3390/ijns10020028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2024] [Revised: 03/12/2024] [Accepted: 03/27/2024] [Indexed: 04/25/2024] Open
Abstract
The aim of this study was to observe the outcomes of newborn screening (NBS) in a certain population by using next-generation sequencing (NGS) as a first-tier screening test combined with tandem mass spectrometry (MS/MS). We performed a multicenter study of 29,601 newborns from eight screening centers with NBS via NGS combined with MS/MS. A custom-designed panel targeting the coding region of the 142 genes of 128 inborn errors of metabolism (IEMs) was applied as a first-tier screening test, and expanded NBS using MS/MS was executed simultaneously. In total, 52 genes associated with the 38 IEMs screened by MS/MS were analyzed. The NBS performance of these two methods was analyzed and compared respectively. A total of 23 IEMs were diagnosed via NGS combined with MS/MS. The incidence of IEMs was approximately 1 in 1287. Within separate statistical analyses, the positive predictive value (PPV) for MS/MS was 5.29%, and the sensitivity was 91.3%. However, for genetic screening alone, the PPV for NGS was 70.83%, with 73.91% sensitivity. The three most common IEMs were methylmalonic academia (MMA), primary carnitine deficiency (PCD) and phenylketonuria (PKU). The five genes with the most common carrier frequencies were PAH (1:42), PRODH (1:51), MMACHC (1:52), SLC25A13 (1:55) and SLC22A5 (1:63). Our study showed that NBS combined with NGS and MS/MS improves the performance of screening methods, optimizes the process, and provides accurate diagnoses.
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Affiliation(s)
- Chengfang Tang
- Department of Guangzhou Newborn Screening Center, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangdong Provincial Clinical Research Center for Child Health, Guangzhou 510180, China;
| | - Lixin Li
- Department of Genetic, Shijiazhuang Maternal and Child Health Hospital, Shijiazhuang 050090, China;
| | - Ting Chen
- Department of Pediatric Endocrinology and Genetic Metabolism, Shanghai Institute for Pediatric Research, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200092, China;
| | - Yulin Li
- Neonatal Disease Screening Center, Jinan Maternity and Child Health Hospital Affiliated to Shandong First Medical University, Jinan 250001, China; (Y.L.); (H.Z.)
| | - Bo Zhu
- Department of Genetics, Inner Mongolia Maternity and Child Health Care Hospital, Hohhot 750306, China; (B.Z.); (X.W.)
| | - Yinhong Zhang
- Department of Medical Genetics, NHC Key Laboratory of Preconception Health Birth in Western China, Yunnan Provincial Key Laboratory for Birth Defects and Genetic Diseases, Yunnan Provincial Clinical Research Center for Birth Defects and Rare Diseases, The First People’s Hospital of Yunnan Province/The Affiliated Hospital of Kunming University of Science and Technology, Kunming 650032, China; (Y.Z.); (B.Z.)
| | - Yifan Yin
- Department of Pediatrics, Chongqing Health Center for Women and Children &Women and Children’s Hospital of Chongqing Medical University, Chongqing 401147, China; (Y.Y.); (J.M.)
| | - Xiulian Liu
- Neonatal Disease Screening Center, Hainan Women and Children’s Medical Center, Haikou 570206, China; (X.L.); (C.H.)
| | - Cidan Huang
- Neonatal Disease Screening Center, Hainan Women and Children’s Medical Center, Haikou 570206, China; (X.L.); (C.H.)
| | - Jingkun Miao
- Department of Pediatrics, Chongqing Health Center for Women and Children &Women and Children’s Hospital of Chongqing Medical University, Chongqing 401147, China; (Y.Y.); (J.M.)
| | - Baosheng Zhu
- Department of Medical Genetics, NHC Key Laboratory of Preconception Health Birth in Western China, Yunnan Provincial Key Laboratory for Birth Defects and Genetic Diseases, Yunnan Provincial Clinical Research Center for Birth Defects and Rare Diseases, The First People’s Hospital of Yunnan Province/The Affiliated Hospital of Kunming University of Science and Technology, Kunming 650032, China; (Y.Z.); (B.Z.)
| | - Xiaohua Wang
- Department of Genetics, Inner Mongolia Maternity and Child Health Care Hospital, Hohhot 750306, China; (B.Z.); (X.W.)
| | - Hui Zou
- Neonatal Disease Screening Center, Jinan Maternity and Child Health Hospital Affiliated to Shandong First Medical University, Jinan 250001, China; (Y.L.); (H.Z.)
| | - Lianshu Han
- Department of Pediatric Endocrinology and Genetic Metabolism, Shanghai Institute for Pediatric Research, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200092, China;
| | - Jizhen Feng
- Department of Genetic, Shijiazhuang Maternal and Child Health Hospital, Shijiazhuang 050090, China;
| | - Yonglan Huang
- Department of Guangzhou Newborn Screening Center, Guangzhou Women and Children’s Medical Center, Guangzhou Medical University, Guangdong Provincial Clinical Research Center for Child Health, Guangzhou 510180, China;
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Esser AJ, Mukherjee S, Dereven‘kov IA, Makarov SV, Jacobsen DW, Spiekerkoetter U, Hannibal L. Versatile Enzymology and Heterogeneous Phenotypes in Cobalamin Complementation Type C Disease. iScience 2022; 25:104981. [PMID: 36105582 PMCID: PMC9464900 DOI: 10.1016/j.isci.2022.104981] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Nutritional deficiency and genetic errors that impair the transport, absorption, and utilization of vitamin B12 (B12) lead to hematological and neurological manifestations. The cblC disease (cobalamin complementation type C) is an autosomal recessive disorder caused by mutations and epi-mutations in the MMACHC gene and the most common inborn error of B12 metabolism. Pathogenic mutations in MMACHC disrupt enzymatic processing of B12, an indispensable step before micronutrient utilization by the two B12-dependent enzymes methionine synthase (MS) and methylmalonyl-CoA mutase (MUT). As a result, patients with cblC disease exhibit plasma elevation of homocysteine (Hcy, substrate of MS) and methylmalonic acid (MMA, degradation product of methylmalonyl-CoA, substrate of MUT). The cblC disorder manifests early in childhood or in late adulthood with heterogeneous multi-organ involvement. This review covers current knowledge on the cblC disease, structure–function relationships of the MMACHC protein, the genotypic and phenotypic spectra in humans, experimental disease models, and promising therapies.
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Kiessling E, Peters F, Ebner LJ, Merolla L, Samardzija M, Baumgartner MR, Grimm C, Froese DS. HIF1 and DROSHA are involved in MMACHC repression in hypoxia. Biochim Biophys Acta Gen Subj 2022; 1866:130175. [DOI: 10.1016/j.bbagen.2022.130175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2022] [Revised: 05/03/2022] [Accepted: 05/23/2022] [Indexed: 11/25/2022]
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Oussalah A, Siblini Y, Hergalant S, Chéry C, Rouyer P, Cavicchi C, Guerrini R, Morange PE, Trégouët D, Pupavac M, Watkins D, Pastinen T, Chung WK, Ficicioglu C, Feillet F, Froese DS, Baumgartner MR, Benoist JF, Majewski J, Morrone A, Rosenblatt DS, Guéant JL. Epimutations in both the TESK2 and MMACHC promoters in the Epi-cblC inherited disorder of intracellular metabolism of vitamin B 12. Clin Epigenetics 2022; 14:52. [PMID: 35440018 PMCID: PMC9020039 DOI: 10.1186/s13148-022-01271-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Accepted: 04/05/2022] [Indexed: 03/14/2023] Open
Abstract
Background epi-cblC is a recently discovered inherited disorder of intracellular vitamin B12 metabolism associating hematological, neurological, and cardiometabolic outcomes. It is produced by an epimutation at the promoter common to CCDC163P and MMACHC, which results from an aberrant antisense transcription due to splicing mutations in the antisense PRDX1 gene neighboring MMACHC. We studied whether the aberrant transcription produced a second epimutation by encompassing the CpG island of the TESK2 gene neighboring CCDC163P.
Methods We unraveled the methylome architecture of the CCDC163P–MMACHC CpG island (CpG:33) and the TESK2 CpG island (CpG:51) of 17 epi-cblC cases. We performed an integrative analysis of the DNA methylome profiling, transcriptome reconstruction of RNA-sequencing (RNA-seq), chromatin immunoprecipitation sequencing (ChIP-Seq) of histone H3, and transcription expression of MMACHC and TESK2.
Results The PRDX1 splice mutations and activation of numerous cryptic splice sites produced antisense readthrough transcripts encompassing the bidirectional MMACHC/CCDC163P promoter and the TESK2 promoter, resulting in the silencing of both the MMACHC and TESK2 genes through the deposition of SETD2-dependent H3K36me3 marks and the generation of epimutations in the CpG islands of the two promoters. Conclusions The antisense readthrough transcription of the mutated PRDX1 produces an epigenetic silencing of MMACHC and TESK2. We propose using the term 'epi-digenism' to define this epigenetic disorder that affects two genes. Epi-cblC is an entity that differs from cblC. Indeed, the PRDX1 and TESK2 altered expressions are observed in epi-cblC but not in cblC, suggesting further evaluating the potential consequences on cancer risk and spermatogenesis. Supplementary Information The online version contains supplementary material available at 10.1186/s13148-022-01271-1.
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Affiliation(s)
- Abderrahim Oussalah
- INSERM UMR_S 1256, Nutrition, Genetics, and Environmental Risk Exposure (NGERE), Faculty of Medicine of Nancy, University of Lorraine, 9 Avenue de la Forêt de Haye, 54000, Nancy, France.,Reference Center for Inborn Errors of Metabolism (ORPHA67872), University Hospital of Nancy, 54000, Nancy, France.,Department of Molecular Medicine, Division of Biochemistry, Molecular Biology and Nutrition, University Hospital of Nancy, 54000, Nancy, France
| | - Youssef Siblini
- INSERM UMR_S 1256, Nutrition, Genetics, and Environmental Risk Exposure (NGERE), Faculty of Medicine of Nancy, University of Lorraine, 9 Avenue de la Forêt de Haye, 54000, Nancy, France
| | - Sébastien Hergalant
- INSERM UMR_S 1256, Nutrition, Genetics, and Environmental Risk Exposure (NGERE), Faculty of Medicine of Nancy, University of Lorraine, 9 Avenue de la Forêt de Haye, 54000, Nancy, France
| | - Céline Chéry
- INSERM UMR_S 1256, Nutrition, Genetics, and Environmental Risk Exposure (NGERE), Faculty of Medicine of Nancy, University of Lorraine, 9 Avenue de la Forêt de Haye, 54000, Nancy, France.,Reference Center for Inborn Errors of Metabolism (ORPHA67872), University Hospital of Nancy, 54000, Nancy, France.,Department of Molecular Medicine, Division of Biochemistry, Molecular Biology and Nutrition, University Hospital of Nancy, 54000, Nancy, France
| | - Pierre Rouyer
- INSERM UMR_S 1256, Nutrition, Genetics, and Environmental Risk Exposure (NGERE), Faculty of Medicine of Nancy, University of Lorraine, 9 Avenue de la Forêt de Haye, 54000, Nancy, France
| | - Catia Cavicchi
- Molecular and Cell Biology Laboratory of Neurometabolic Diseases, Paediatric Neurology Unit and Laboratories, Meyer Children's Hospital, Viale Pieraccini 24, 50139, Florence, Italy
| | - Renzo Guerrini
- Molecular and Cell Biology Laboratory of Neurometabolic Diseases, Paediatric Neurology Unit and Laboratories, Meyer Children's Hospital, Viale Pieraccini 24, 50139, Florence, Italy.,Department of NEUROFARBA, University of Florence, Florence, Italy
| | - Pierre-Emmanuel Morange
- INSERM UMR_S 1263, Center for CardioVascular and Nutrition Research (C2VN), Aix-Marseille University, 13385, Marseille, France
| | - David Trégouët
- INSERM, BPH, U1219, Université Bordeaux, 33000, Bordeaux, France
| | - Mihaela Pupavac
- Department of Human Genetics, McGill University and Research Institute, McGill University Health Centre, Montreal, QC, H4A 3J1, Canada
| | - David Watkins
- Department of Human Genetics, McGill University and Research Institute, McGill University Health Centre, Montreal, QC, H4A 3J1, Canada
| | - Tomi Pastinen
- Department of Human Genetics, McGill University and Research Institute, McGill University Health Centre, Montreal, QC, H4A 3J1, Canada
| | - Wendy K Chung
- Departments of Pediatrics and Medicine, Columbia University, New York, USA
| | - Can Ficicioglu
- Children's Hospital of Philadelphia, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
| | - François Feillet
- INSERM UMR_S 1256, Nutrition, Genetics, and Environmental Risk Exposure (NGERE), Faculty of Medicine of Nancy, University of Lorraine, 9 Avenue de la Forêt de Haye, 54000, Nancy, France.,Reference Center for Inborn Errors of Metabolism (ORPHA67872), University Hospital of Nancy, 54000, Nancy, France
| | - D Sean Froese
- Division of Metabolism, University Children's Hospital, University of Zürich, Zürich, Switzerland
| | - Matthias R Baumgartner
- Division of Metabolism, University Children's Hospital, University of Zürich, Zürich, Switzerland
| | - Jean-François Benoist
- Biochemistry Hormonology Laboratory, Robert-Debré University Hospital, APHP, 48 bd Serurier, 75019, Paris, France
| | - Jacek Majewski
- Department of Human Genetics, McGill University and Research Institute, McGill University Health Centre, Montreal, QC, H4A 3J1, Canada
| | - Amelia Morrone
- Molecular and Cell Biology Laboratory of Neurometabolic Diseases, Paediatric Neurology Unit and Laboratories, Meyer Children's Hospital, Viale Pieraccini 24, 50139, Florence, Italy.,Department of NEUROFARBA, University of Florence, Florence, Italy
| | - David S Rosenblatt
- Department of Human Genetics, McGill University and Research Institute, McGill University Health Centre, Montreal, QC, H4A 3J1, Canada
| | - Jean-Louis Guéant
- INSERM UMR_S 1256, Nutrition, Genetics, and Environmental Risk Exposure (NGERE), Faculty of Medicine of Nancy, University of Lorraine, 9 Avenue de la Forêt de Haye, 54000, Nancy, France. .,Reference Center for Inborn Errors of Metabolism (ORPHA67872), University Hospital of Nancy, 54000, Nancy, France. .,Department of Molecular Medicine, Division of Biochemistry, Molecular Biology and Nutrition, University Hospital of Nancy, 54000, Nancy, France. .,Department of Hepato-Gastroenterology, University Hospital of Nancy, 54000, Nancy, France.
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Hannibal L, Jacobsen DW. Intracellular processing of vitamin B 12 by MMACHC (CblC). VITAMINS AND HORMONES 2022; 119:275-298. [PMID: 35337623 DOI: 10.1016/bs.vh.2022.02.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Vitamin B12 (cobalamin, Cbl, B12) is a water-soluble micronutrient synthesized exclusively by a group of microorganisms. Human beings are unable to make B12 and thus obtain the vitamin via intake of animal products, fermented plant-based foods or supplements. Vitamin B12 obtained from the diet comprises three major chemical forms, namely hydroxocobalamin (HOCbl), methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl). The most common form of B12 present in supplements is cyanocobalamin (CNCbl). Yet, these chemical forms cannot be utilized directly as they come, but instead, they undergo chemical processing by the MMACHC protein, also known as CblC. Processing of dietary B12 by CblC involves removal of the upper-axial ligand (beta-ligand) yielding the one-electron reduced intermediate cob(II)alamin. Newly formed cob(II)alamin undergoes trafficking and delivery to the two B12-dependent enzymes, cytosolic methionine synthase (MS) and mitochondrial methylmalonyl-CoA mutase (MUT). The catalytic cycles of MS and MUT incorporate cob(II)alamin as a precursor to regenerate the coenzyme forms MeCbl and AdoCbl, respectively. Mutations and epimutations in the MMACHC gene result in cblC disease, the most common inborn error of B12 metabolism, which manifests with combined homocystinuria and methylmalonic aciduria. Elevation of metabolites homocysteine and methylmalonic acid occurs because the lack of an active CblC blocks formation of the indispensable precursor cob(II)alamin that is necessary to activate MS and MUT. Thus, in patients with cblC disease, vitamin B12 is absorbed and present in circulation in normal to high concentrations, yet, cells are unable to make use of it. Mutations in seemingly unrelated genes that modify MMACHC gene expression also result in clinical phenotypes that resemble cblC disease. We review current knowledge on structural and functional aspects of intracellular processing of vitamin B12 by the versatile protein CblC, its partners and possible regulators.
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Affiliation(s)
- Luciana Hannibal
- Laboratory of Clinical Biochemistry and Metabolism, Department of General Pediatrics, Adolescent Medicine and Neonatology, Faculty of Medicine, Medical Center-University of Freiburg, Freiburg, Germany.
| | - Donald W Jacobsen
- Department of Cardiovascular and Metabolic Sciences, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
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Epimutation in inherited metabolic disorders: the influence of aberrant transcription in adjacent genes. Hum Genet 2022; 141:1309-1325. [PMID: 35190856 DOI: 10.1007/s00439-021-02414-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2021] [Accepted: 12/08/2021] [Indexed: 12/12/2022]
Abstract
Epigenetic diseases can be produced by a stable alteration, called an epimutation, in DNA methylation, in which epigenome alterations are directly involved in the underlying molecular mechanisms of the disease. This review focuses on the epigenetics of two inherited metabolic diseases, epi-cblC, an inherited metabolic disorder of cobalamin (vitamin B12) metabolism, and alpha-thalassemia type α-ZF, an inherited disorder of α2-globin synthesis, with a particular interest in the role of aberrant antisense transcription of flanking genes in the generation of epimutations in CpG islands of gene promoters. In both disorders, the epimutation is triggered by an aberrant antisense transcription through the promoter, which produces an H3K36me3 histone mark involved in the recruitment of DNA methyltransferases. It results from diverse genetic alterations. In alpha-thalassemia type α-ZF, a deletion removes HBA1 and HBQ1 genes and juxtaposes the antisense LUC7L gene to the HBA2 gene. In epi-cblC, the epimutation in the MMACHC promoter is produced by mutations in the antisense flanking gene PRDX1, which induces a prolonged antisense transcription through the MMACHC promoter. The presence of the epimutation in sperm, its transgenerational inheritance via the mutated PRDX1, and the high expression of PRDX1 in spermatogonia but its nearly undetectable transcription in spermatids and spermatocytes, suggest that the epimutation could be maintained during germline reprogramming and despite removal of aberrant transcription. The epivariation seen in the MMACHC promoter (0.95 × 10-3) is highly frequent compared to epivariations affecting other genes of the Online Catalog of Human Genes and Genetic Disorders in an epigenome-wide dataset of 23,116 individuals. This and the comparison of epigrams of two monozygotic twins suggest that the aberrant transcription could also be influenced by post-zygotic environmental exposures.
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