Fig.1.

Histological stainings and immunolabelling of frozen sections and an electron micrograph of the muscle biopsy from the Proband. A) Haematoxylin and eosin staining showing a wide variation in fibre size with internal nuclei in several small fibres. Excess endomysial connective tissue or necrosis were not detected. B) Gömöri trichrome staining showing a population of small fibres containing red stained rods. C) Cytochrome C oxidase staining showing a population of darkly stained small type 1 fibres and some small weakly stained fibres. D) Immunolabelling with a monoclonal antibody to fetal myosin showing several very small positive fibres. E-F) Immunolabelling with monoclonal antibodies to fast (E) and slow (F) myosin heavy chains showing a population of small fibres that only express slow myosin (^*), larger fibres that express fast (f) and several hybrid fibres with varying intensity that express both fast and slow myosin (+). G) Electron micrograph showing a fibre with severely disrupted myofibrils, an internal nucleus, small rods (arrow) and clusters of mitochondria (m), and less severely affected fibres either side (^*) without rods.