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Neuromuscular disorders
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
The cause of the disease is inappropriate expression of DUX4, a gene on 4q that is usually repressed in muscle by subtelomeric repeats on 4q but which is transcribed inappropriately if deletion reduces the number of these repeats (FSHD1). Homology with subtelomeric repeats on 10q made the recognition of this pattern difficult to achieve and can make it more difficult to achieve accurate diagnostic results. In a small minority of patients (with FSHD2), the disease mechanism is mutation in a separate chromatin structural protein gene (SMCHD1) that is needed to regulate DUX4 in combination with a PAS (polyadenylation signal) on chromosome 4q. Inheritance is therefore digenic in FSHD2. Although complex, molecular tests are usually able to confirm the diagnosis and to enable prenatal diagnosis, although this is requested by only a minority of families.
Ophthalmological Manifestations of Hereditary Myopathies
Published in Journal of Binocular Vision and Ocular Motility, 2022
Marta Saint-Gerons, Miguel Angel Rubio, Gemma Aznar, Ana Matheu
FSHD1 is an autosomal dominant disorder caused by a deletion of a variable number of tandem D4Z4 repeats located in chromosome 4. FSHD2 form is caused by mutations, in the SMCHD1 gene, the chromatin regulator, or in the DNMT3B gene.75,76 The median age of onset is 29–32 years, but it can begin in infancy or later in adulthood.77,78 Facioscapulohumeral muscular dystrophy (FSHD) is characterized by progressive muscle weakness with the involvement of the face, scapula, upper arms, tibial and axial muscles. Extra muscular involvement may occur and include sensorineural hearing loss, and rarely, cognitive impairment or seizures. Vascular anomalies have been described and include microaneurysm, tortuosity of arterial retinal vessels, foveal hypoplasia, telangiectasias, vascular anomalies in the retinal periphery that mimics Coats disease, and electroretinogram alterations.79 Other ophthalmological findings are ptosis, lagophthalmos, and reduced intraocular pressure.80,81