| Abstract: | Myopathy with minicores in siblings A muscle biopsy from a 5 year old boy with a myopathic disorder showed a wide range of fibre diameters, Type 1 fibre predominance and focal loss of ‘ATPase’ activity in some fibres. Electron microscopy showed, in about 10% of fibres, localized distortions and loss of Z-lines within compactly grouped myofibrils with preservation of glycogen and mitochondria. His younger sibling, aged 1 year, who was only mildly hypotonic, showed similar but less marked abnormalities on muscle biopsy. These changes are those described in ‘multicore disease’, but it is suggested that the term ‘minicore’ might be more appropriate to avoid confusion with central core disease in which multiple cores are often found. Because of the preservation of mitochondria and glycogen, and the slightly atypical staining of Type 1 fibres it is suggested that the disorder might be caused by an abnormality of myosin or actin. |
