Facioscapulohumeral Muscular Dystrophy

Excerpt

Clinical characteristics: Facioscapulohumeral muscular dystrophy (FSHD) typically presents with weakness of the facial muscles, 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: The diagnosis of FSHD1 is established in a proband with characteristic clinical features by identification of a heterozygous pathogenic contraction of the D4Z4 repeat array in the subtelomeric region of chromosome 4q35 on a chromosome 4 permissive haplotype. The diagnosis of FSHD2 is established in a proband by identification of hypomethylation of the D4Z4 repeat array in the subtelomeric region of chromosome 4q35 on a chromosome 4 permissive haplotype. Hypomethylation of the D4Z4 repeat array can be the result of a heterozygous pathogenic variant in SMCHD1 or DNMT3B.

Management: Treatment of manifestations: Consultation with a physical therapist to establish appropriate exercise regimen; ankle/foot orthoses to improve mobility and prevent falls; occupational and speech therapy in individuals with infantile onset; surgical fixation of the scapula to the chest wall may improve range of motion of the arms over the short term; management of chronic pain by physical therapy and medication; monitoring respiratory function; lubricants to prevent drying of the sclera or taping the eyes shut during sleep to treat exposure keratitis; treatment for retinal vasculopathy as per ophthalmologist; standard treatment of sensorineural hearing loss.

Surveillance: Annual physical therapy assessment; Pain should be assessed at regular visits to the primary care physician or physical therapist; screening for hypoventilation in individuals with abnormal PFTs, severe proximal weakness, kyphoscoliosis, wheelchair dependence, or comorbid disease affecting ventilation; pulmonary consultation for FVC <60%, excessive daytime somnolence or nonrestorative sleep, and prior to surgical procedures requiring anesthesia; annual dilated ophthalmoscopy in individuals with early childhood-onset FSHD with large pathogenic contraction of D4Z4 and adults with visual symptoms; audiometry in infants at each visit and annually in children.

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 a pregnancy at increased risk is possible if the D4Z4 pathogenic contraction has been identified in the family. FSHD2 is inherited in a digenic manner.