The FSHD2 Gene SMCHD1 Is a Modifier of Disease Severity in Families Affected by FSHD1
2013; Elsevier BV; Volume: 93; Issue: 4 Linguagem: Inglês
10.1016/j.ajhg.2013.08.004
ISSN1537-6605
AutoresSabrina Sacconi, Richard J.L.F. Lemmers, Judit Balog, Patrick J. van der Vliet, Pauline Lahaut, Merlijn P. van Nieuwenhuizen, Kirsten R. Straasheijm, Rashmie D. Debipersad, Marianne Vos-Versteeg, Leonardo Salviati, Alberto Casarin, Elena Pegoraro, Rabi Tawil, Egbert Bakker, Stephen J. Tapscott, Claude Desnuelle, Silvère M. van der Maarel,
Tópico(s)Attention Deficit Hyperactivity Disorder
ResumoFacioscapulohumeral muscular dystrophy type 1 (FSHD1) is caused by contraction of the D4Z4 repeat array on chromosome 4 to a size of 1–10 units. The residual number of D4Z4 units inversely correlates with clinical severity, but significant clinical variability exists. Each unit contains a copy of the DUX4 retrogene. Repeat contractions are associated with changes in D4Z4 chromatin structure that increase the likelihood of DUX4 expression in skeletal muscle, but only when the repeat resides in a genetic background that contains a DUX4 polyadenylation signal. Mutations in the structural maintenance of chromosomes flexible hinge domain containing 1 (SMCHD1) gene, encoding a chromatin modifier of D4Z4, also result in the increased likelihood of DUX4 expression in individuals with a rare form of FSHD (FSHD2). Because SMCHD1 directly binds to D4Z4 and suppresses somatic expression of DUX4, we hypothesized that SMCHD1 may act as a genetic modifier in FSHD1. We describe three unrelated individuals with FSHD1 presenting an unusual high clinical severity based on their upper-sized FSHD1 repeat array of nine units. Each of these individuals also carries a mutation in the SMCHD1 gene. Familial carriers of the FSHD1 allele without the SMCHD1 mutation were only mildly affected, suggesting a modifier effect of the SMCHD1 mutation. Knocking down SMCHD1 in FSHD1 myotubes increased DUX4 expression, lending molecular support to a modifier role for SMCHD1 in FSHD1. We conclude that FSHD1 and FSHD2 share a common pathophysiological pathway in which the FSHD2 gene can act as modifier for disease severity in families affected by FSHD1. Facioscapulohumeral muscular dystrophy type 1 (FSHD1) is caused by contraction of the D4Z4 repeat array on chromosome 4 to a size of 1–10 units. The residual number of D4Z4 units inversely correlates with clinical severity, but significant clinical variability exists. Each unit contains a copy of the DUX4 retrogene. Repeat contractions are associated with changes in D4Z4 chromatin structure that increase the likelihood of DUX4 expression in skeletal muscle, but only when the repeat resides in a genetic background that contains a DUX4 polyadenylation signal. Mutations in the structural maintenance of chromosomes flexible hinge domain containing 1 (SMCHD1) gene, encoding a chromatin modifier of D4Z4, also result in the increased likelihood of DUX4 expression in individuals with a rare form of FSHD (FSHD2). Because SMCHD1 directly binds to D4Z4 and suppresses somatic expression of DUX4, we hypothesized that SMCHD1 may act as a genetic modifier in FSHD1. We describe three unrelated individuals with FSHD1 presenting an unusual high clinical severity based on their upper-sized FSHD1 repeat array of nine units. Each of these individuals also carries a mutation in the SMCHD1 gene. Familial carriers of the FSHD1 allele without the SMCHD1 mutation were only mildly affected, suggesting a modifier effect of the SMCHD1 mutation. Knocking down SMCHD1 in FSHD1 myotubes increased DUX4 expression, lending molecular support to a modifier role for SMCHD1 in FSHD1. We conclude that FSHD1 and FSHD2 share a common pathophysiological pathway in which the FSHD2 gene can act as modifier for disease severity in families affected by FSHD1. Facioscapulohumeral muscular dystrophy (FSHD [MIM 158900]) is one of the three most common muscular dystrophies in adults with an estimated prevalence of 1:20,000.1Padberg, G.W. (1982). Facioscapulohumeral disease. PhD thesis, Leiden University, Leiden.Google Scholar Individuals with FSHD have facial, shoulder girdle, and upper extremity weakness that can spread with progression of the disease to abdominal, humeral, anterior lower leg muscles, and (in more severely affected individuals) to pelvic girdle muscles. The peculiar involvement of specific muscles is such a striking feature that it often distinguishes FSHD from other forms of muscular dystrophy.2Padberg G.W. Lunt P.W. Koch M. Fardeau M. Diagnostic criteria for facioscapulohumeral muscular dystrophy.Neuromuscul. Disord. 1991; 1: 231-234Abstract Full Text PDF PubMed Scopus (188) Google Scholar The disease usually becomes manifest in the second decade, but the progression and severity are highly variable with one-fifth of affected individuals becoming wheelchair dependent while an equal proportion of gene carriers remain asymptomatic throughout their lives.3Pandya S. King W.M. Tawil R. Facioscapulohumeral dystrophy.Phys. Ther. 2008; 88: 105-113Crossref PubMed Scopus (54) Google Scholar Autosomal-dominant FSHD1 represents the most common form, accounting for at least 95% of cases.4Upadhyaya M. Maynard J. Rogers M.T. Lunt P.W. Jardine P. Ravine D. Harper P.S. 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Neurol. 1996; 39: 744-748Crossref PubMed Scopus (167) Google Scholar Gender differences may also account for variability in clinical severity with males being more severely affected then females.1Padberg, G.W. (1982). Facioscapulohumeral disease. PhD thesis, Leiden University, Leiden.Google Scholar, 13Zatz M. Marie S.K. Cerqueira A. Vainzof M. Pavanello R.C. Passos-Bueno M.R. The facioscapulohumeral muscular dystrophy (FSHD1) gene affects males more severely and more frequently than females.Am. J. Med. Genet. 1998; 77: 155-161Crossref PubMed Scopus (98) Google Scholar The marked intrafamilial clinical variability further suggests the involvement of other genetic or environmental factors that modify the disease severity of a commonly inherited contraction size. A minimum of one D4Z4 repeat is required to develop FSHD, suggesting that the repeat itself plays a critical role in the development of the disease.14Tupler R. Berardinelli A. Barbierato L. Frants R. Hewitt J.E. Lanzi G. 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Genet. 2009; 18: 2414-2430Crossref PubMed Scopus (172) Google Scholar In the absence of this DUX4 PAS, such as on 4qB chromosomes and on chromosome 10 where a highly homologous repeat array resides, transcriptional derepression of the FSHD locus does not normally lead to the production of stable DUX4 transcripts or to the appearance of FSHD clinical phenotype.29Lemmers R.J. van der Vliet P.J. Klooster R. Sacconi S. Camaño P. Dauwerse J.G. Snider L. Straasheijm K.R. van Ommen G.J. Padberg G.W. et al.A unifying genetic model for facioscapulohumeral muscular dystrophy.Science. 2010; 329: 1650-1653Crossref PubMed Scopus (521) Google Scholar, 31Lemmers R.J. Wohlgemuth M. Frants R.R. Padberg G.W. Morava E. van der Maarel S.M. Contractions of D4Z4 on 4qB subtelomeres do not cause facioscapulohumeral muscular dystrophy.Am. J. Hum. Genet. 2004; 75: 1124-1130Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar A small group of individuals with FSHD show D4Z4 chromatin changes and DUX4 derepression in skeletal muscle in the absence of repeat array contraction. These individuals with FSHD2 (MIM 158901) carry at least one FSHD-permissive 4qA allele and are clinically identical to individuals with FSHD1.22de Greef J.C. Lemmers R.J. Camaño P. Day J.W. Sacconi S. Dunand M. van Engelen B.G. Kiuru-Enari S. Padberg G.W. Rosa A.L. et al.Clinical features of facioscapulohumeral muscular dystrophy 2.Neurology. 2010; 75: 1548-1554Crossref PubMed Scopus (135) Google Scholar, 23van Overveld P.G. Lemmers R.J. Sandkuijl L.A. Enthoven L. Winokur S.T. Bakels F. Padberg G.W. van Ommen G.J. Frants R.R. van der Maarel S.M. Hypomethylation of D4Z4 in 4q-linked and non-4q-linked facioscapulohumeral muscular dystrophy.Nat. Genet. 2003; 35: 315-317Crossref PubMed Scopus (301) Google Scholar, 32de Greef J.C. Lemmers R.J. van Engelen B.G. Sacconi S. Venance S.L. Frants R.R. Tawil R. van der Maarel S.M. Common epigenetic changes of D4Z4 in contraction-dependent and contraction-independent FSHD.Hum. Mutat. 2009; 30: 1449-1459Crossref PubMed Scopus (142) Google Scholar Unlike families with FSHD1 where the chromatin changes are mostly occurring on the contracted allele, in families with FSHD2, D4Z4 chromatin relaxation occurs on the D4Z4 repeat arrays of both chromosomes 4 and 10. Recently we showed that in the majority of families with FSHD2, the disease is caused by digenic inheritance of a DUX4 PAS-containing chromosome 4 and a mutation in the structural maintenance of chromosomes flexible hinge domain containing 1 (SMCHD1 [MIM 614982]) gene on chromosome 18.33Lemmers R.J. Tawil R. Petek L.M. Balog J. Block G.J. Santen G.W. Amell A.M. van der Vliet P.J. Almomani R. 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Genet. 2012; 44: 1370-1374Crossref PubMed Scopus (414) Google Scholar Because both FSHD1 and FSHD2 result from the somatic derepression of DUX4, we investigated whether SMCHD1 may act as a modifier for disease severity in families with FSHD1 and may have a role in the marked variability of clinical expression that is encountered in some families. Previous studies were only partially successful in explaining the variation in clinical severity in individuals with FSHD1. In addition to the inverse correlation with the residual repeat size,9Goto K. Lee J.H. Matsuda C. Hirabayashi K. Kojo T. Nakamura A. Mitsunaga Y. Furukawa T. Sahashi K. Arahata K. DNA rearrangements in Japanese facioscapulohumeral muscular dystrophy patients: clinical correlations.Neuromuscul. Disord. 1995; 5: 201-208Abstract Full Text PDF PubMed Scopus (38) Google Scholar, 11Ricci E. Galluzzi G. Deidda G. Cacurri S. Colantoni L. Merico B. Piazzo N. Servidei S. Vigneti E. 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Neurol. 2005; 58: 569-576Crossref PubMed Scopus (99) Google Scholar To identify modifiers of disease severity, of particular interest are those families with FSHD1 carrying upper-sized D4Z4 repeat arrays of 8–10 units, as shown by the fact that carriers of these alleles are more likely to have a partial or less severe form of FSHD or to be asymptomatic.40Butz M. Koch M.C. Müller-Felber W. Lemmers R.J. van der Maarel S.M. Schreiber H. Facioscapulohumeral muscular dystrophy. Phenotype-genotype correlation in patients with borderline D4Z4 repeat numbers.J. Neurol. 2003; 250: 932-937Crossref PubMed Scopus (55) Google Scholar, 41Felice K.J. Whitaker C.H. The clinical features of facioscapulohumeral muscular dystrophy associated with borderline (>/=35 kb) 4q35 EcoRI fragments.J. Clin. Neuromuscul. Dis. 2005; 6: 119-126Crossref PubMed Scopus (6) Google Scholar, 42Scionti I. Fabbri G. Fiorillo C. Ricci G. Greco F. D’Amico R. Termanini A. Vercelli L. Tomelleri G. Cao M. et al.Facioscapulohumeral muscular dystrophy: new insights from compound heterozygotes and implication for prenatal genetic counselling.J. Med. Genet. 2012; 49: 171-178Crossref PubMed Scopus (44) Google Scholar To explore the possibility that mutations in SMCHD1 may modify the disease severity in families affected by FSHD1, we investigated the SMCHD1 locus in six unrelated individuals with FSHD1 from a cohort of 53 independent families with FSHD1 which carried a FSHD allele of 8–10 D4Z4 units. These individuals were selected based on D4Z4 methylation levels <25% indicative for FSHD2.33Lemmers R.J. Tawil R. Petek L.M. Balog J. Block G.J. Santen G.W. Amell A.M. van der Vliet P.J. Almomani R. Straasheijm K.R. et al.Digenic inheritance of an SMCHD1 mutation and an FSHD-permissive D4Z4 allele causes facioscapulohumeral muscular dystrophy type 2.Nat. Genet. 2012; 44: 1370-1374Crossref PubMed Scopus (414) Google Scholar We report that three of them have a mutation in SMCHD1 although in the remaining cases the cause for D4Z4 hypomethylation remains to be identified. These three cases have a repeat array of nine D4Z4 units on a FSHD-permissive DUX4 PAS-containing chromosome and show an unusually severe clinical presentation of the disease based on clinical evaluation that included manual muscle testing of 60 muscles and determination of the clinical severity score.39van Overveld P.G. Enthoven L. Ricci E. Rossi M. Felicetti L. Jeanpierre M. Winokur S.T. Frants R.R. Padberg G.W. van der Maarel S.M. Variable hypomethylation of D4Z4 in facioscapulohumeral muscular dystrophy.Ann. Neurol. 2005; 58: 569-576Crossref PubMed Scopus (99) Google Scholar The relevant biometric and genetic observations in these families are summarized in Table 1 and Table S1 available online. Pedigrees and genetic analyses of these three families are presented in Figure 1A. Signed and informed consent was obtained from all participants and family members according to protocols approved by the Institutional Ethics Review Boards of the University Hospital of Nice and collaborating institutes.Table 1Clinical and Biometric Data of the Three FamiliesRfNrSexAAEAge at OnsetCSSMMT ScoreDiagnosisRf1021I-1M71unknownaThese patients do not report any symptoms.3261/300FSHD1I-2F67unknownaThese patients do not report any symptoms.4255/300FSHD2II-1M48121065/300FSHD1+FSHD2II-2F38–0300/300unaffectedIII-1F15–0300/300unaffectedIII-2M656198/300FSHD1+FSHD2Rf1110I-1M5561055/300FSHD1+FSHD2I-2F53–0300/300unaffectedII-1F26245280/300FSHD2II-2M21unknownaThese patients do not report any symptoms.2269/300FSHD1Rf1121II-1M67151075/300FSHD1+FSHD2Abbreviations are as follows: CSS, clinical severity score; AAE, age at the last examination; MMT, manual muscle testing.a These patients do not report any symptoms. Open table in a new tab Abbreviations are as follows: CSS, clinical severity score; AAE, age at the last examination; MMT, manual muscle testing. In the first family (Rf1021), the proband (II-1) has been followed in our Center since the age of 35 when he became wheelchair dependent. He started to experience asymmetric scapular weakness at the age of 18, but he reported inability to blow into a flute at the age of 12. During the last examination, at age 48, he presented with severe and asymmetric facial weakness of orbicularis oculi and oris, marked shoulder girdle weakness associated with bilateral scapular winging, and humeral weakness. He displays marked hyperlordosis resulting from abdominal muscle weakness and weakness and atrophy of lower legs. Distal upper limb muscles are also becoming involved. He has a clinical severity score (CSS) of 10.11Ricci E. Galluzzi G. Deidda G. Cacurri S. Colantoni L. Merico B. Piazzo N. Servidei S. Vigneti E. Pasceri V. et al.Progress in the molecular diagnosis of facioscapulohumeral muscular dystrophy and correlation between the number of KpnI repeats at the 4q35 locus and clinical phenotype.Ann. Neurol. 1999; 45: 751-757Crossref PubMed Scopus (231) Google Scholar Genetic analysis showed that this proband carries a nine D4Z4 unit 4A161 allele, confirming the diagnosis of FSHD1. His 6-year-old son (III-2) was referred to our Center because of difficulties in raising his arms and a history of frequent falls. At examination he presented with weakness of the orbicularis oculi muscles, mild shoulder girdle weakness with scapular winging, Gower’s sign, and asymmetric foot dorsiflexor weakness (CSS 6). We also examined the proband’s daughter (III-1), 15 years old, and concluded that she
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