Sarcotubular myopathy: A newly recognized, benign, congenital, familial muscle disease

Two brothers, presently 15 and 11 years old, of a Hutterite colony and consanguineous parentage have had nonprogressive muscle weakness since infancy. The electromyogram was myopathic in the older and nondiagnostic in the younger. Serum enzymes of muscle origin were normal in the younger but the creatine phosphokinase level was elevated in the older one. Both siblings had a vacuolar myopathy. Type II fibers were selectively affected. Myriad small spaces appeared in abnormal fibers in the transverse sections, while in longitudinal sections the vacuolation was segmental in distribution. The abnormal spaces were less than 6 μ wide and reacted negatively for glycogen, lipids, acid mucopolysaccharides, and acid phosphatase. In the electron microscope the spaces were membrane-bound and were either empty or contained membrane fragments and traces of amorphous material. Larger spaces arose by coalescence of adjacent smaller ones. With the aid of cytochemical markers, the limiting membrances of the abnormal spaces were found to be reactive for the sarcoplasmic reticulum-associated ATPase. Peroxidase-loaded transverse tubules often abutted on, encircled, or were invaginated into the abnormal spaces. In the vacuolated fibers the concentration of nondilated sarcotubular profiles was significantly increased over that seen in fibers from normal control subjects.