The significance of minimal alterations in muscle biopsy of Duchenne carriers.

In order to define the significance of minimal histological and ultrastructural abnormalities in Duchenne carriers, 18 normal healthy volunteers were examined by muscle biopsy. Light microscopy evidenced occasional internal nuclei and less frequent small round and angular fibres. Variability of fibre size, increase in connective tissue, necroses and basophilia found in carriers were not present in controls. Histograms constructed on ATPase stain sections demonstrated variability in distribution of fibre types both in normals and in carriers. Fibre size was more variable in carriers, where a significant decrease of the size of type II B fibres was observed. Electron microscopy evidenced knots in overcontraction, myofibrillary widening, subsarcolemmal accumulation of mitochondria and Z band streaming, which have been reported also in carriers. The results are discussed and compared with the data of the literature.