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Calpena E, Wurmser M, McGowan SJ, Atique R, Bertola DR, Cunningham ML, Gustafson JA, Johnson D, Morton JEV, Passos-Bueno MR, Timberlake AT, Lifton RP, Wall SA, Twigg SRF, Maire P, Wilkie AOM. Unexpected role of SIX1 variants in craniosynostosis: expanding the phenotype of SIX1-related disorders. J Med Genet 2022; 59:165-169. [PMID: 33436522 PMCID: PMC8273188 DOI: 10.1136/jmedgenet-2020-107459] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 12/07/2020] [Accepted: 12/09/2020] [Indexed: 01/19/2023]
Abstract
BACKGROUND Pathogenic heterozygous SIX1 variants (predominantly missense) occur in branchio-otic syndrome (BOS), but an association with craniosynostosis has not been reported. METHODS We investigated probands with craniosynostosis of unknown cause using whole exome/genome (n=628) or RNA (n=386) sequencing, and performed targeted resequencing of SIX1 in 615 additional patients. Expression of SIX1 protein in embryonic cranial sutures was examined in the Six1nLacZ/+ reporter mouse. RESULTS From 1629 unrelated cases with craniosynostosis we identified seven different SIX1 variants (three missense, including two de novo mutations, and four nonsense, one of which was also present in an affected twin). Compared with population data, enrichment of SIX1 loss-of-function variants was highly significant (p=0.00003). All individuals with craniosynostosis had sagittal suture fusion; additionally four had bilambdoid synostosis. Associated BOS features were often attenuated; some carrier relatives appeared non-penetrant. SIX1 is expressed in a layer basal to the calvaria, likely corresponding to the dura mater, and in the mid-sagittal mesenchyme. CONCLUSION Craniosynostosis is associated with heterozygous SIX1 variants, with possible enrichment of loss-of-function variants compared with classical BOS. We recommend screening of SIX1 in craniosynostosis, particularly when sagittal±lambdoid synostosis and/or any BOS phenotypes are present. These findings highlight the role of SIX1 in cranial suture homeostasis.
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Affiliation(s)
- Eduardo Calpena
- Clinical Genetics Group, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - Maud Wurmser
- Institut Cochin, INSERM, CNRS, Université de Paris, Paris, France
| | - Simon J McGowan
- Centre for Computational Biology, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - Rodrigo Atique
- Centro de Estudos do Genoma Humano, Universidade de São Paulo, São Paulo, Brazil
| | - Débora R Bertola
- Unidade de Genética Clínica, Instituto da Criança do Hospital das Clínicas, Faculdade de Medicina da Universidade de São Paulo, São Paulo, Brazil
- Instituto de Biociências, Universidade de São Paulo, São Paulo, São Paulo, Brazil
| | - Michael L Cunningham
- Center for Developmental Biology and Regenerative Medicine, Seattle Children's Research Institute, Seattle, Washington, USA
- Seattle Children's Craniofacial Center, Seattle Children's Hospital, and Department of Pediatrics, Division of Craniofacial Medicine, University of Washington, Seattle, Washington, USA
| | - Jonas A Gustafson
- Center for Developmental Biology and Regenerative Medicine, Seattle Children's Research Institute, Seattle, Washington, USA
| | - David Johnson
- Craniofacial Unit, Oxford University Hospitals NHS Foundation Trust, Oxford, UK
| | - Jenny E V Morton
- West Midlands Regional Clinical Genetics Service and Birmingham Health Partners, Birmingham Women's and Children's Hospitals NHS Foundation Trust, Birmingham, UK
| | | | - Andrew T Timberlake
- Hansjörg Wyss Department of Plastic Surgery, New York University Langone Medical Center, New York, New York, USA
| | | | - Steven A Wall
- Craniofacial Unit, Oxford University Hospitals NHS Foundation Trust, Oxford, UK
| | - Stephen R F Twigg
- Clinical Genetics Group, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - Pascal Maire
- Institut Cochin, INSERM, CNRS, Université de Paris, Paris, France
| | - Andrew O M Wilkie
- Clinical Genetics Group, MRC Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
- Craniofacial Unit, Oxford University Hospitals NHS Foundation Trust, Oxford, UK
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