Myopathy with unique ultrastructural feature in Marinesco-Sjögren syndrome.

We have investigated 3 children aged 6, 3, and 2 years, from 2 families, with the clinical features of Marinesco-Sjögren syndrome. Muscle biopsy specimens from all 3 were abnormal and showed small vacuoles and slight variation in fiber size. Electron microscopy revealed vacuolation and membranous whorls and, in particular, a unique dense membranous structure associated with nuclei. These cases emphasize the involvement of muscle in Marinesco-Sjögren syndrome and the importance of electron microscopy in differential diagnosis.