Myotubular myopathy: morphological, immunohistochemical and clinical variation.

Myotubular myopathy frequently presents in male infants with severe generalised muscular hypotonia and weakness associated with ventilatory insufficiency, and is diagnosed on biopsy by the presence of many fibres with central nuclei and mitochondrial aggregation. In a 6-year period, we have investigated five unrelated patients with clinical and pathological features suggesting an X-linked myotubular myopathy, including one female patient. In one male infant, a biopsy of vastus lateralis showed less than 2% centrally-nucleated fibres, while biceps brachii showed up to 15% centrally-nucleated fibres. Immunohistochemical expression of the neural cell adhesion molecule (CD56) was more intense in the biceps muscle than in vastus lateralis, while expression of desmin and vimentin was similar. Morphometric evaluation of tissue from each of the patients revealed a wide spread of values for the number of centrally-nucleated fibres per microscopic field, and variation in the extent of immunohistochemical expression of NCAM, utrophin, laminin alpha 5 chain, vimentin and HLA1 antigen. These variations in the manifestations of myotubular myopathy have not been previously described, and will need to be correlated with the increasing knowledge of the mutations in the MTM1 gene coding for myotubularin.