X-linked myotubular myopathy: clinical and pathological findings in a family.

A five-generation family with recessively inherited X-linked myotubular myopathy was investigated. Two of the affected boys, who were siblings and were verified by muscle biopsy to have the disease, died 3 days and 3 months, respectively, after birth. They showed marked hypotonus from birth, general muscle weakness and asphyxia. Three other boys, who were probably affected by the disease, had severe asphyxia and died shortly after birth. In three of the five cases there was polyhydramnios. The muscle biopsies of the two siblings revealed predominance of small fibres with central nuclei and accumulation of mitochondria in the central parts of the fibres. In one of the boys mainly the type 1 fibres were hypotrophic. The postmortem examination revealed variation in the involvement of different muscles, the anterior tibial muscle being the most severely affected. Intrafusal muscle fibres and myocardium were apparently unaffected. There was no involvement of the spinal cord. The clinical examination of two obligate carriers in the family revealed no muscle weakness but the muscle biopsy showed pathological changes including greatly increased variability of fibre size, and many fibres with central nuclei. The findings indicate that muscle biopsy is of value in genetic counselling to detect carriers although the observed changes were unspecific.