Which muscular dystrophy is classically associated with scapulohumeral weakness and facial weakness due to D4Z4 repeat contraction on 4q35?

• A. Facioscapulohumeral muscular dystrophy type 1 (FSHD1)
• B. Duchenne muscular dystrophy
• C. Becker muscular dystrophy
• D. Limb-girdle muscular dystrophy type 1B

Answer: (A)

The pattern being tested is a muscular dystrophy with a distinctive scapulohumeral weakness plus facial weakness that arises from a specific genetic change on 4q35. In facioscapulohumeral muscular dystrophy type 1, contraction of the D4Z4 repeat array on 4q35 reduces epigenetic silencing and, with a permissive 4qA haplotype, allows expression of the DUX4 gene in muscle. This leads to progressive weakness of facial muscles and of the shoulder girdle, producing scapular winging that is characteristic of this condition. It is typically autosomal dominant and often begins in adolescence or early adulthood.

This contrasts with Duchenne and Becker muscular dystrophy, which are X-linked dystrophinopathies presenting with proximal weakness in early childhood and other features like calf pseudohypertrophy, and with other limb-girdle patterns that lack the classic facial involvement and scapulohumeral distribution.