Objective: To report clinical, morphologic, and immunohistochemical studies on autosomal dominant, clinically nonprogressive, and not previously described progressive forms of hyaline body (HB) myopathy (HBM) in a Saudi Arabian kindred.

Results: Muscle biopsies from four patients showed HB in type 1 fibers; they were positive for ATPase at pH 4.3/4.6 and for heavy chain slow myosin (HCSM); some HB were HCSM negative. HB were nonreactive for αB-crystallin, ubiquitin, tropomyosin, actins, desmin, and components of sarcolemma. Ultrastructurally, HB were granular and filamentous or amorphous, often with fragments of sarcomeres, and surrounded by a zone of sarcomeric disorganization. All biopsies showed “myopathic” changes, angulated neurogenic fibers, and fiber type grouping. There was no correlation between HB and course of disease; the progressive cases displayed more severe myopathic features.

Conclusions: Formation of hyaline bodies in hyaline body myopathy is associated with either myolysis or defective incorporation of heavy chain slow myosin into the cytoskeleton. Hyaline bodies very likely contain additional unidentified proteins. Neurogenic factors are also involved in the hyaline body myopathy pathogenesis.