Sarcoplasmic body myopathy

Sammanfattning: In 1980 a new hereditary myopathy with adult onset was described in a swedish family. The most characteristic feature of this myopathy was the sarcoplasmic inclusion bodies (SB), seen in the muscle biopsies. Distal muscle weakness seemed to be the most prominent early symptom. In this paper we have further analysed the phenotype to distinguish the different stages of myopathy; from a subclinical stage to a fully developed myopathy with patients requiring wheelchair for ambulation. We have found that even the subclinical cases have these specific sarcoplasmic bodies in their muscle biopsies together with elevated creatine kinase (CK) levels. The sarcoplasmic bodies from the symptom-free carriers have now been thoroughly studied by transmission electron microscopy on epoxy embedded material, supplemented with ultrastructural immuno cytochemistry on muscle tissue from one patient. The SB´s were found to be of different shapes, from homogenous electrondense structures, with distinct borders, to a more mottled appearance. It was earlier suggested that mutant, abnormal stable desmin might be the cause of the sarcoplasmic bodies due to deficient break-down of desmin. A mutation of the desmin gene has now been excluded as a possible cause of this myopathy. It seems, however to be a dramatic upregulation of desmin and also of vimentin in the highly affected patients. The increase of vimentin might be explained by upregulation in immature regenerating muscle cells. However, the cause of elevated desmin levels is more difficult to explain. The presence of sarcoplasmic bodies, as a presymptomatic phenomenon, mostly combined with increase in CK, is helpful in establishing possible carriership of the mutant gene in symptomfree family members.