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Goossens R, van den Boogaard ML, Lemmers RJLF, Balog J, van der Vliet PJ, Willemsen IM, Schouten J, Maggio I, van der Stoep N, Hoeben RC, Tapscott SJ, Geijsen N, Gonçalves MAFV, Sacconi S, Tawil R, van der Maarel SM. Intronic SMCHD1 variants in FSHD: testing the potential for CRISPR-Cas9 genome editing. J Med Genet 2019; 56:828-837. [PMID: 31676591 DOI: 10.1136/jmedgenet-2019-106402] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Revised: 09/04/2019] [Accepted: 09/21/2019] [Indexed: 01/14/2023]
Abstract
BACKGROUND Facioscapulohumeral dystrophy (FSHD) is associated with partial chromatin relaxation of the DUX4 retrogene containing D4Z4 macrosatellite repeats on chromosome 4, and transcriptional de-repression of DUX4 in skeletal muscle. The common form of FSHD, FSHD1, is caused by a D4Z4 repeat array contraction. The less common form, FSHD2, is generally caused by heterozygous variants in SMCHD1. METHODS We employed whole exome sequencing combined with Sanger sequencing to screen uncharacterised FSHD2 patients for extra-exonic SMCHD1 mutations. We also used CRISPR-Cas9 genome editing to repair a pathogenic intronic SMCHD1 variant from patient myoblasts. RESULTS We identified intronic SMCHD1 variants in two FSHD families. In the first family, an intronic variant resulted in partial intron retention and inclusion of the distal 14 nucleotides of intron 13 into the transcript. In the second family, a deep intronic variant in intron 34 resulted in exonisation of 53 nucleotides of intron 34. In both families, the aberrant transcripts are predicted to be non-functional. Deleting the pseudo-exon by CRISPR-Cas9 mediated genome editing in primary and immortalised myoblasts from the index case of the second family restored wild-type SMCHD1 expression to a level that resulted in efficient suppression of DUX4. CONCLUSIONS The estimated intronic mutation frequency of almost 2% in FSHD2, as exemplified by the two novel intronic SMCHD1 variants identified here, emphasises the importance of screening for intronic variants in SMCHD1. Furthermore, the efficient suppression of DUX4 after restoring SMCHD1 levels by genome editing of the mutant allele provides further guidance for therapeutic strategies.
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Affiliation(s)
- Remko Goossens
- Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | | | | | - Judit Balog
- Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | | | - Iris M Willemsen
- Human Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Julie Schouten
- Hubrecht Institute-KNAW and University Medical Center, Utrecht, The Netherlands.,Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht, The Netherlands
| | - Ignazio Maggio
- Department of Cell and Chemical Biology, Leiden University Medical Center, Leiden, The Netherlands.,Department of Pediatrics, Leiden University Medical Center, Leiden, The Netherlands
| | - Nienke van der Stoep
- Center for Human and Clinical Genetics, Leiden University Medical Center, Leiden, The Netherlands
| | - Rob C Hoeben
- Department of Cell and Chemical Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - Stephen J Tapscott
- Division of Biology, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
| | - Niels Geijsen
- Hubrecht Institute-KNAW and University Medical Center, Utrecht, The Netherlands.,Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht, The Netherlands
| | - Manuel A F V Gonçalves
- Department of Cell and Chemical Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - Sabrina Sacconi
- Peripheral Nervous System, Muscle and ALS Department, Université Côte d'Azur, Nice, France.,Institute for Research on Cancer and Aging of Nice, Faculty of Medicine, Université Côte d'Azur, Nice, France
| | - Rabi Tawil
- Department of Neurology, University of Rochester Medical Center, Rochester, New York, USA
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