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Palmer EE, Carroll R, Shaw M, Kumar R, Minoche AE, Leffler M, Murray L, Macintosh R, Wright D, Troedson C, McKenzie F, Townshend S, Ward M, Nawaz U, Ravine A, Runke CK, Thorland EC, Hummel M, Foulds N, Pichon O, Isidor B, Le Caignec C, Demeer B, Andrieux J, Albarazi SH, Bye A, Sachdev R, Kirk EP, Cowley MJ, Field M, Gecz J. RLIM Is a Candidate Dosage-Sensitive Gene for Individuals with Varying Duplications of Xq13, Intellectual Disability, and Distinct Facial Features. Am J Hum Genet 2020; 107:1157-1169. [PMID: 33159883 PMCID: PMC7820564 DOI: 10.1016/j.ajhg.2020.10.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2020] [Accepted: 10/13/2020] [Indexed: 12/21/2022] Open
Abstract
Interpretation of the significance of maternally inherited X chromosome variants in males with neurocognitive phenotypes continues to present a challenge to clinical geneticists and diagnostic laboratories. Here we report 14 males from 9 families with duplications at the Xq13.2-q13.3 locus with a common facial phenotype, intellectual disability (ID), distinctive behavioral features, and a seizure disorder in two cases. All tested carrier mothers had normal intelligence. The duplication arose de novo in three mothers where grandparental testing was possible. In one family the duplication segregated with ID across three generations. RLIM is the only gene common to our duplications. However, flanking genes duplicated in some but not all the affected individuals included the brain-expressed genes NEXMIF, SLC16A2, and the long non-coding RNA gene FTX. The contribution of the RLIM-flanking genes to the phenotypes of individuals with different size duplications has not been fully resolved. Missense variants in RLIM have recently been identified to cause X-linked ID in males, with heterozygous females typically having normal intelligence and highly skewed X chromosome inactivation. We detected consistent and significant increase of RLIM mRNA and protein levels in cells derived from seven affected males from five families with the duplication. Subsequent analysis of MDM2, one of the targets of the RLIM E3 ligase activity, showed consistent downregulation in cells from the affected males. All the carrier mothers displayed normal RLIM mRNA levels and had highly skewed X chromosome inactivation. We propose that duplications at Xq13.2-13.3 including RLIM cause a recognizable but mild neurocognitive phenotype in hemizygous males.
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Affiliation(s)
- Elizabeth E Palmer
- Genetics of Learning Disability Service, Waratah, NSW 2298, Australia; School of Women's and Children's Health, UNSW Medicine, University of New South Wales, Randwick, NSW 2031, Australia; Sydney Children's Hospital, Randwick, NSW 2031, Australia; Kinghorn Centre for Clinical Genomics, Garvan Institute, Darlinghurst, Sydney, NSW 2010, Australia.
| | - Renee Carroll
- Adelaide Medical School and the Robinson Research Institute, University of Adelaide, Adelaide, SA 5000, Australia
| | - Marie Shaw
- Adelaide Medical School and the Robinson Research Institute, University of Adelaide, Adelaide, SA 5000, Australia
| | - Raman Kumar
- Adelaide Medical School and the Robinson Research Institute, University of Adelaide, Adelaide, SA 5000, Australia
| | - Andre E Minoche
- St Vincent's Clinical School, University of New South Wales, Sydney, NSW 2010, Australia
| | - Melanie Leffler
- Genetics of Learning Disability Service, Waratah, NSW 2298, Australia
| | - Lucinda Murray
- Genetics of Learning Disability Service, Waratah, NSW 2298, Australia
| | | | - Dale Wright
- Discipline of Genomic Medicine and Discipline of Child & Adolescent Health, University of Sydney, Sydney, NSW 2010, Australia; Department of Cytogenetics, The Children's Hospital at Westmead, Westmead, NSW 2145, Australia
| | - Chris Troedson
- Children's Hospital at Westmead, Sydney, NSW 2145, Australia
| | - Fiona McKenzie
- School of Paediatrics and Child Health, University of Western Australia, Perth, WA 6009, Australia; Genetic Services of Western Australia, Perth, WA 6008, Australia
| | | | - Michelle Ward
- Genetic Services of Western Australia, Perth, WA 6008, Australia
| | - Urwah Nawaz
- Adelaide Medical School and the Robinson Research Institute, University of Adelaide, Adelaide, SA 5000, Australia
| | - Anja Ravine
- Department of Cytogenetics, The Children's Hospital at Westmead, Westmead, NSW 2145, Australia; Pathwest Laboratory Medicine WA, Perth, WA 6008, Australia
| | - Cassandra K Runke
- Genomics Laboratory, Department of Laboratory Medicine and Pathology, Mayo Clinic, Scottsdale, AZ 85259, USA
| | - Erik C Thorland
- Genomics Laboratory, Department of Laboratory Medicine and Pathology, Mayo Clinic, Scottsdale, AZ 85259, USA
| | - Marybeth Hummel
- West Virginia University School of Medicine, Department of Pediatrics, Section of Medical Genetics Morgantown, WV 26506-9600, USA
| | - Nicola Foulds
- Wessex Clinical Genetics Services, Southampton SO16 5YA, UK
| | - Olivier Pichon
- Service de génétique médicale - Unité de Génétique Clinique, CHU de Nantes - Hôtel Dieu, Nantes 44093, France
| | - Bertrand Isidor
- Service de génétique médicale - Unité de Génétique Clinique, CHU de Nantes - Hôtel Dieu, Nantes 44093, France
| | - Cédric Le Caignec
- Service de génétique médicale, Institut fédératif de Biologie, CHU Hopital Purpan, Toulouse 31059, France
| | - Bénédicte Demeer
- Center for Human Genetics, CLAD Nord de France, CHU Amiens-Picardie, Amiens 80080, France; CHIMERE EA 7516, University Picardie Jules Verne, Amiens 80025, France
| | - Joris Andrieux
- Institut de Biochimie et Génétique Moléculaire, CHU Lille, Lille 59000, France
| | | | - Ann Bye
- School of Women's and Children's Health, UNSW Medicine, University of New South Wales, Randwick, NSW 2031, Australia; Sydney Children's Hospital, Randwick, NSW 2031, Australia
| | - Rani Sachdev
- School of Women's and Children's Health, UNSW Medicine, University of New South Wales, Randwick, NSW 2031, Australia; Sydney Children's Hospital, Randwick, NSW 2031, Australia
| | - Edwin P Kirk
- School of Women's and Children's Health, UNSW Medicine, University of New South Wales, Randwick, NSW 2031, Australia; Sydney Children's Hospital, Randwick, NSW 2031, Australia
| | - Mark J Cowley
- Children's Cancer Institute, Lowy Cancer Research Centre, University of New South Wales, Randwick, NSW 2033, Australia
| | - Mike Field
- Genetics of Learning Disability Service, Waratah, NSW 2298, Australia
| | - Jozef Gecz
- Adelaide Medical School and the Robinson Research Institute, University of Adelaide, Adelaide, SA 5000, Australia; Healthy Mothers, Babies and Children, South Australian Health and Medical Research Institute, Adelaide, SA 5000, Australia.
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Bansal P, Kondaveeti Y, Pinter SF. Forged by DXZ4, FIRRE, and ICCE: How Tandem Repeats Shape the Active and Inactive X Chromosome. Front Cell Dev Biol 2020; 7:328. [PMID: 32076600 PMCID: PMC6985041 DOI: 10.3389/fcell.2019.00328] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Accepted: 11/26/2019] [Indexed: 12/11/2022] Open
Abstract
Recent efforts in mapping spatial genome organization have revealed three evocative and conserved structural features of the inactive X in female mammals. First, the chromosomal conformation of the inactive X reveals a loss of topologically associated domains (TADs) present on the active X. Second, the macrosatellite DXZ4 emerges as a singular boundary that suppresses physical interactions between two large TAD-depleted "megadomains." Third, DXZ4 reaches across several megabases to form "superloops" with two other X-linked tandem repeats, FIRRE and ICCE, which also loop to each other. Although all three structural features are conserved across rodents and primates, deletion of mouse and human orthologs of DXZ4 and FIRRE from the inactive X have revealed limited impact on X chromosome inactivation (XCI) and escape in vitro. In contrast, loss of Xist or SMCHD1 have been shown to impair TAD erasure and gene silencing on the inactive X. In this perspective, we summarize these results in the context of new research describing disruption of X-linked tandem repeats in vivo, and discuss their possible molecular roles through the lens of evolutionary conservation and clinical genetics. As a null hypothesis, we consider whether the conservation of some structural features on the inactive X may reflect selection for X-linked tandem repeats on account of necessary cis- and trans-regulatory roles they may play on the active X, rather than the inactive X. Additional hypotheses invoking a role for X-linked tandem repeats on X reactivation, for example in the germline or totipotency, remain to be assessed in multiple developmental models spanning mammalian evolution.
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Affiliation(s)
- Prakhar Bansal
- Department of Genetics and Genome Sciences, School of Medicine, UCONN Health, University of Connecticut, Farmington, CT, United States
- Institute for Systems Genomics, University of Connecticut, Farmington, CT, United States
| | - Yuvabharath Kondaveeti
- Department of Genetics and Genome Sciences, School of Medicine, UCONN Health, University of Connecticut, Farmington, CT, United States
- Institute for Systems Genomics, University of Connecticut, Farmington, CT, United States
| | - Stefan F. Pinter
- Department of Genetics and Genome Sciences, School of Medicine, UCONN Health, University of Connecticut, Farmington, CT, United States
- Institute for Systems Genomics, University of Connecticut, Farmington, CT, United States
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