X-linked recessive myotubular myopathy: I. Clinical and pathologic findings in a family.

Four neonatal deaths in one family were due to X-linked myotubular myopathy. The characteristic alterations in muscle, described in three cases, are marked fiber hypotrophy, size variability, and the presence of internal nuclei or pale areas. The diagnosis can be verified only by obtaining a careful genetic history. Previous occurrence of male neonatal death or stillbirth, or of hypotonia and respiratory insufficiency, is critical in the identification of suspected cases. There is morphologic justification for retaining the name "myotubular myopathy" to distinguish this X-linked disorder from other congenital conditions involving muscle weakness that have similar morphologic features.