The intracranial and orbital pathology and muscle pathology of chromosome 12-linked congenital fibrosis of the extraocular muscles are described in 3 affected members of a family in a report from Children’s Hospital, Harvard Medical School, Boston, and other centers. Postmortem examination of 1 and muscle biopsies of 2 patients showed abnormalities in the brain stem, cranial nerves, and extraocular muscles (EOMs): absence of motor neurons of the oculomotor nucleus, loss of axons in III cranial nerve, absence of the superior division of III CN, and atrophic superior rectus and levator palpebrae muscles, showing only a clump of myofibers, connective tissue, and fat. Increased numbers of internal nuclei and central mitochondrial clumping found in other extraocular muscles pointed to an extension of the process beyond the superior division of III CN, and an abnormal development of the EOM lower motor neuron system. 
COMMENT. Congenital fibrosis of extraocular muscles, an autosomal dominant inherited disorder, is characterized by bilateral ptosis and fixation of eyes in a downward and strabismic position. It resembles Brown’s syndrome (vertical retraction), and Duane’s syndrome (horizontal retraction), associated with fibrosis and aberrant innervation of the rectus lateralis. The pathology of these congenital EOM fibrosis syndromes is more diffuse than previously recognized and extends beyond the extraocular muscles and involves also the cranial nerves and brain stem.