[Benign congenital myopathy with type I fiber predominance and rare "cores" in the asymptomatic mother. Association with malformations of the midline (author's transl)].

The case of a 20 year-old female with a congenital myopathy and multiple midline malformations (cranio-facial dysplasia with cleft-palate, cervical and dorsal vertebral blocks and sacro-lumbar spina bifida) is reported. A muscle biopsy showed only a predominance of type I fibres (97,3 p. 100). A muscle biopsy from the asymptomatic mother showed a predominance of type I fibres (95 p. 100) and a small number of fibres (less than 5 p. 100) with central or peripheral cores. Other fibres showed subsarcolemnic mitochondrial aggregates and slight architectural alterations. These findings confirm the variable histological patterns in benign congenital myopathies and emphasize the usefulness of studying the asymptomatic parents of such patients in whom a predominance of type I fibres is the only change present in the muscle biopsy.