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      Haploinsufficiency of the FOXA2 associated with a complex clinical phenotype

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          Abstract

          Background

          There are few reports describing the proximal deletions of the short arm of chromosome 20, making it difficult to predict the likely consequences of these deletions. Most previously reported cases have described the association of 20p11.2 deletions with Alagille syndrome, while there are others that include phenotypes such as panhypopituitarism, craniofacial dysmorphism, polysplenia, autism, and Hirschsprung disease.

          Methods

          Molecular karyotyping, cytogenetics, and DNA sequencing were undertaken in a child to study the genetic basis of a complex phenotype consisting of craniofacial dysmorphism, ocular abnormalities, ectopic inguinal testes, polysplenia, growth hormone deficiency, central hypothyroidism, and gastrointestinal system anomalies.

          Results

          We report the smallest described de novo proximal 20p11.2 deletion, which deletes only the FOXA2 leading to the above complex phenotype.

          Conclusions

          Haploinsufficiency of the FOXA2 only gene is associated with a multisystem disorder.

          Abstract

          Haploinsufficiency of the FOXA2 leads to a complex phenotype consisting of craniofacial dysmorphism, ocular abnormalities, ectopic inguinal testes, polysplenia, growth hormone deficiency, central hypothyroidism, and gastrointestinal system anomalies.

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          Most cited references28

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          The Foxa family of transcription factors in development and metabolism.

          The Foxa subfamily of winged helix/forkhead box (Fox) transcription factors has been the subject of genetic and biochemical study for over 15 years. During this time its three members, Foxa1, Foxa2 and Foxa3, have been found to play important roles in multiple stages of mammalian life, beginning with early development, continuing during organogenesis, and finally in metabolism and homeostasis in the adult. Foxa2 is required for the formation of the node and notochord, and in its absence severe defects in gastrulation, neural tube patterning, and gut morphogenesis result in embryonic lethality. Foxa1 and Foxa2 cooperate to establish competence in foregut endoderm and are required for normal development of endoderm-derived organs such as the liver, pancreas, lungs, and prostate. In post-natal life, members of the Foxa family control glucose metabolism through the regulation of multiple target genes in the liver, pancreas, and adipose tissue. Insight into the unique molecular basis of Foxa function has been obtained from recent genetic and genomic data, which identify the Foxa proteins as 'pioneer factors' whose binding to promoters and enhancers enable chromatin access for other tissue-specific transcription factors.
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            Dynamic regulation of Pdx1 enhancers by Foxa1 and Foxa2 is essential for pancreas development.

            The onset of pancreas development in the foregut endoderm is marked by activation of the homeobox gene Pdx1 (IPF1). Pdx1 is essential for the expansion of the pancreatic primordium and the development of endocrine islets. The control of Pdx1 expression has been only partially elucidated. We demonstrate here that the winged-helix transcription factors Foxa1 and Foxa2 co-occupy multiple regulatory domains in the Pdx1 gene. Compound conditional ablation of both Foxa1 and Foxa2 in the pancreatic primordium results in complete loss of Pdx1 expression and severe pancreatic hypoplasia. Mutant mice exhibit hyperglycemia with severely disrupted acinar and islet development, and die shortly after birth. Assessment of developmental markers in the mutant pancreas revealed a failure in the expansion of the pancreatic anlage, a blockage of exocrine and endocrine cell differentiation, and an arrest at the primitive duct stage. Comparing their relative developmental activity, we find that Foxa2 is the major regulator in promoting pancreas development and cell differentiation. Using chromatin immunoprecipitations (ChIP) and ChIP sequencing (ChIPSeq) of fetal pancreas and islet chromatin, we demonstrate that Foxa1 and Foxa2 predominantly occupy a distal enhancer at -6.4 kb relative to the transcriptional start site in the Pdx1 gene. In addition, occupancy of the well-characterized proximal Pdx1 enhancer by Foxa1 and Foxa2 is developmental stage-dependent. Thus, the regulation of Pdx1 expression by Foxa1 and Foxa2 is a key early event controlling the expansion and differentiation of the pancreatic primordia.
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              HNF-3 beta is essential for node and notochord formation in mouse development.

              HNF-3 beta, a member of the HNF-3/fork head family of transcription factors, is expressed in the node, notochord, floor plate, and gut in mouse embryos. A null mutation of this gene leads to embryonic lethality. The primary defect of HNF-3 beta -/- embryos is an absence of organized node and notochord formation, which leads to secondary defects in dorsal-ventral patterning of the neural tube. In contrast, patterning along the anterior-posterior axis was surprisingly little affected. Although HNF-3 beta is required for node and notochord formation, some organizer activity persists in the absence of these structures. HNF-3 beta is not required for the development of definitive endoderm cells, but foregut morphogenesis is severely affected in HNF-3 beta -/- embryos.
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                Author and article information

                Contributors
                khussain@sidra.org
                Journal
                Mol Genet Genomic Med
                Mol Genet Genomic Med
                10.1002/(ISSN)2324-9269
                MGG3
                Molecular Genetics & Genomic Medicine
                John Wiley and Sons Inc. (Hoboken )
                2324-9269
                11 April 2020
                June 2020
                : 8
                : 6 ( doiID: 10.1002/mgg3.v8.6 )
                : e1086
                Affiliations
                [ 1 ] College of Health & Life Sciences Hamad Bin Khalifa University Doha Qatar
                [ 2 ] Division of Endocrinology Department of Pediatric Medicine Sidra Medicine Doha Qatar
                [ 3 ] Department of Radiology Sidra Medicine Doha Qatar
                [ 4 ] Division of Pathology Genetics Department of Pathology Sidra Medicine Doha Qatar
                [ 5 ] Diagnostic Genomic Division Department of Laboratory Medicine and Pathology Hamad Medical Corporation Doha Qatar
                Author notes
                [*] [* ] Correspondence

                Khalid Hussain, Department of Pediatrics, Division of Endocrinology, Sidra Medicine, Al Luqta Street, Education City, North Campus, Doha, Qatar.

                Email: khussain@ 123456sidra.org

                Author information
                https://orcid.org/0000-0002-3010-309X
                https://orcid.org/0000-0002-5480-7112
                Article
                MGG31086
                10.1002/mgg3.1086
                7284027
                32277595
                042e7927-96dc-4558-a92f-d262d3aa287b
                © 2019 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals, Inc.

                This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 16 September 2019
                : 06 November 2019
                : 14 November 2019
                Page count
                Figures: 5, Tables: 2, Pages: 8, Words: 4403
                Funding
                Funded by: Qatar National Library
                Categories
                Original Article
                Original Articles
                Custom metadata
                2.0
                June 2020
                Converter:WILEY_ML3GV2_TO_JATSPMC version:5.8.4 mode:remove_FC converted:10.06.2020

                20p11.2 deletion,foxa2,growth hormone deficiency,haploinsufficiency,hypothyroidism

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