This section of soleus muscle demonstrates the striations characteristic of skeletal muscle. The early or infantile form presents as a floppy infant at birth. The juvenile form is the most common and presents in late infancy with slowly progressive muscle weakness. The adult form has a relatively benign course. It has an X-linked recessive form of inheritance.
Affected infants are severely hypotonic with respiratory distress.
All of these features were present in the current case. The gene for this disorder was localized by positional cloning to Xq28, corresponding to the myotubularin locus. A variety of mutations were discovered in patients with X-linked centronuclear myopathy, including point mutations, deletions, and splice mutations. The possibility of detecting mutations and determining carrier status in a disease with a high proportion of sporadic cases is of importance for genetic counselling. More than half of these mutations are expected to inactivate the putative enzymatic activity of myotubularin, either by truncation or by missense mutations affecting the predicted PTP domain.