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FSHD type 2 and Bosma arhinia microphthalmia syndrome: Two faces of the same mutation

Karlien Mul¹, Richard J L F Lemmers², Marjolein Kriek²

¹From the Department of Neurology (K.M., N.C.V., B.G.M.v.E., C.G.C.H.), Radboud University Medical Center, Nijmegen; Departments of Human Genetics (R.J.L.F.L., P.J.v.d.V., M.L.v.d.B., S.M.v.d.M.), Clinical Genetics (M.K.), and Neurology (U.A.B.), Leiden University Medical Center, Leiden, the Netherlands; Department of Pediatrics (J.M.G.), Cedars Sinai Medical Center, Los Angeles, CA; Department of Medical Genetics (A.E.L.), MassGeneral Hospital for Children, Boston, MA; Center for Genomic Medicine and Department of Neurology (H.B.), Massachusetts General Hospital, Boston; Department of Pathology (S.A.M.), University of Iowa Hospitals and Clinics, Iowa City; The John Walton Muscular Dystrophy Research Centre (K.J., T.E., A.T., V.S.), Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK; Neuromuscular Consult Unit (S.K.G.), Bilbo-Basurtu Erakunde Sanitario Integratua, Organización Sanitaria Integrada Bilbao-Basurto, Spain; Centre de Référence des Maladies Neuromusculaires (S.S.), Nice, France; Department of Neurology (R.T.), University of Rochester Medical Center, NY; Division of Human Biology (S.J.T.), Fred Hutchinson Cancer Research Center, Seattle, WA; and National Institute of Environmental Health Sciences (N.D.S.), Research Triangle Park, NC. karlien.mul@radboudumc.nl.

|July 8, 2018

Abstract

Objective:

To determine whether congenital arhinia/Bosma arhinia microphthalmia syndrome (BAMS) and facioscapulohumeral muscular dystrophy type 2 (FSHD2), 2 seemingly unrelated disorders both caused by heterozygous pathogenic missense variants in the SMCHD1 gene, might represent different ends of a broad single phenotypic spectrum associated with SMCHD1 dysfunction.

Methods:

We examined and/or interviewed 14 patients with FSHD2 and 4 unaffected family members with N-terminal SMCHD1 pathogenic missense variants to identify BAMS subphenotypes.

Results:

None of the patients with FSHD2 or family members demonstrated any congenital defects or dysmorphic features commonly found in patients with BAMS. One patient became anosmic after nasal surgery and one patient was hyposmic; one man was infertile (unknown cause) but reported normal pubertal development.

Conclusion:

These data suggest that arhinia/BAMS and FSHD2 do not represent one phenotypic spectrum and that SMCHD1 pathogenic variants by themselves are insufficient to cause either of the 2 disorders. More likely, both arhinia/BAMS and FSHD2 are caused by complex oligogenic or multifactorial mechanisms that only partially overlap at the level of SMCHD1.

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