A newly recognized disease of skeletal muscle was discovered recently in a 4-year-old girl.1,2 The child had congenital, apparently nonprogressive, muscular weakness that was more severe proximally. In her biopsied skeletal muscle fibers were abnormal rod-shaped structures, which cytochemically appeared to be altered myofibrillar material. By electron microscopy, the rods were found to be pathologic fibrils with an axial periodicity of 145 A and were, therefore, thought to be related to myosin or one of its components.A second example of this disease has now been found in a 16-year-old girl. The early clinical and most of the pathological features were identical, indicating that the disease is similar, but the course in later childhood of this second case showed that her condition was slowly progressive.
The methods for histopathology and histo- and cytochemistry were as described previously.2,1 An additional histochemical method for sarcoplasmic reticulum (SR) triad