Muscle biopsy without centrally located nuclei in a male child with mild X-linked myotubular myopathy.

In children with a myopathy, muscle biopsy, together with the clinical presentation, can guide further investigations. The presence of centrally located nuclei suggests a myotubular myopathy, and gene testing may confirm this diagnosis. We describe a male child with a mild form of X-linked myotubular myopathy for which repeated muscle biopsy did not show the characteristic pattern of centrally located nuclei. Myotubular myopathy was not contemplated, therefore, until a maternally related relative was shown to have the disorder. Genetic testing showed that the index case carried the same mutation in his MTM1 gene as this relative.