MSH: An autosomal dominant degenerative muscle disease characterized by slowly progressive weakness of the muscles of the face, upper-arm, and shoulder girdle. The onset of symptoms usually occurs in the first or second decade of life. Affected individuals usually present with impairment of upper extremity elevation. This tends to be followed by facial weakness, primarily involving the orbicularis oris and orbicularis oculi muscles. (Neuromuscul Disord 1997;7(1):55-62; Adams et al., Principles of Neurology, 6th ed, p1420),NCI: An autosomal dominant disorder affecting the skeletal muscles of the face, scapula, and upper arm. Patients present with muscle weakness in these anatomic areas. The muscle weakness eventually spreads to other skeletal muscles as well.