Facioscapulohumeral muscular dystrophy (FSHD)
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A 20-year-old has difficulty whistling and raising his arms above his head. He has scapular winging and facial weakness.
AD
- FSHD1: D4Z4 repeat contraction on 4q35 (1-10 repeats vs normal 11-100)
- FSHD2: SMCHD1 variants + permissive 4qA haplotype
- Facial weakness (difficulty whistling, closing eyes)
- Scapular winging, shoulder weakness
- Asymmetric
- Onset usually adolescence/young adult
- Slow progression
- Clinical recognition: descending, often asymmetric facial, scapular, and humeral weakness
- Serum creatine kinase normal to mildly elevated; muscle biopsy/EMG nonspecific (genetic testing has largely replaced them)
- Confirm with specialized testing for FSHD1, a contracted D4Z4 repeat (1-10 units) on a permissive 4qA allele at 4q35; if negative, test SMCHD1 for FSHD2. Standard multigene myopathy panels do not detect the repeat contraction
- No disease-modifying therapy; supportive multidisciplinary care
- Physical therapy, low-impact exercise, ankle-foot orthoses for foot drop, and scapular fixation surgery in selected patients
- Screen for and treat retinal vasculopathy (Coats-like) and sensorineural hearing loss (especially infantile-onset); monitor respiratory function in those with severe or axial involvement
"FSHD = Face, Shoulder, Humerus, Down (foot drop)": The name tells you the muscles affected: facial weakness, scapular (shoulder) winging, and humeral (upper arm) weakness. Foot dorsiflexor weakness is also common.
"DUX4 is the culprit in both types": Both FSHD1 (D4Z4 repeat contraction) and FSHD2 (SMCHD1/DNMT3B variants) lead to inappropriate reactivation of the DUX4 gene, which is normally silent in adult skeletal muscle.