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Facioscapulohumeral Muscular Dystrophy.

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GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2018.
1999 Mar 8 [updated 2014 Mar 20].

Author information

1
Department of Human and Clinical Genetics, Leiden University Medical Center, Leiden, The Netherlands
2
Department of Pediatrics, Division of Genetic Medicine, University of Washington, Seattle, Washington

Excerpt

CLINICAL CHARACTERISTICS:

Facioscapulohumeral muscular dystrophy (FSHD) typically presents before age 20 years with weakness of the facial muscles and the stabilizers of the scapula or the dorsiflexors of the foot. Severity is highly variable. Weakness is slowly progressive and approximately 20% of affected individuals eventually require a wheelchair. Life expectancy is not shortened.

DIAGNOSIS/TESTING:

Although some controversy remains, FSHD is likely caused by inappropriate expression of the double homeobox-containing gene DUX4 in muscle cells. DUX4 lies in the macrosatellite repeat D4Z4 on chromosome 4q35, which has a length between 11 and 100 repeat units on normal alleles. Approximately 95% of individuals with FSHD have a D4Z4 allele of between one and ten repeat units. The shortening of the D4Z4 allele causes chromatin relaxation at the D4Z4 locus and DUX4 promoter and thereby derepression of DUX4. This common form of FSHD is designated facioscapulohumeral muscular dystrophy 1 (FSHD1). Molecular genetic testing measures the length of the D4Z4 allele. About 5% of individuals with FSHD show chromatin relaxation at D4Z4 without having a D4Z4 contraction. In these individuals with so-called FSHD2, pathogenic variants in the chromatin modifier SMCHD1 cause the chromatin relaxation at D4Z4.

MANAGEMENT:

Treatment of manifestations: Consultation with a physical therapist; low-intensity aerobic exercise; management of chronic pain by physical therapy and medication, as necessary; ventilator support for hypoventilation; standard treatment of sensorineural hearing loss; lubricants to prevent drying of the sclera or taping the eyes shut during sleep to treat exposure keratitis; ankle/foot orthoses to improve mobility and prevent falls. Surgical fixation of the scapula to the chest wall may improve range of motion of the arms over the short term. Surveillance: Pain should be assessed at regular visits to the primary care physician or physical therapist; routine screening for hypoventilation and yearly forced vital capacity in those with moderate to severe disease; periodic hearing screening in affected children; annual dilated ophthalmoscopy in childhood.

GENETIC COUNSELING:

FSHD1 is inherited in an autosomal dominant manner. Approximately 70%-90% of individuals have inherited the disease-causing deletion from a parent, and approximately 10%-30% of affected individuals have FSHD as the result of a de novo deletion. Offspring of an affected individual have a 50% chance of inheriting the deletion. Prenatal testing for pregnancies at increased risk is possible if the D4Z4 pathogenic contraction has been identified in the family. FSHD2 is inherited in a digenic manner.

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