In the course of clinical practice, one encounters a remarkable number of restricted disorders of the nervous system, many of which are transmitted from generation to generation as a mendelian, usually dominant, trait. Of the more severe ones, only a few of the more striking examples are described here. Milder and more restricted conditions, such as stuttering and dyslexia, that are pervasive in the population are described in Chap. 27. The reader may turn to books on genetics or teratology for an account of such oddities as hereditary unilateral ptosis, hereditary Horner syndrome, pupillary inequalities, jaw winking, and absence of a particular skeletal muscle.
The syndrome of congenital facial diplegia with convergent strabismus is referred to as Möbius syndrome, although Von Graefe had described it earlier. Its presence at birth is disclosed by the lack of facial movements and of full eye closure. A review of the subject in the English literature was written by Henderson, and a more recent analysis of 37 affected individuals was written by Harriëtte and colleagues. In Henderson’s study of 61 cases of the congenital facial diplegia syndrome, there were 45 instances of associated abducens palsy, 15 of complete external ophthalmoplegia, 18 of lingual palsy, 17 of clubfeet, 13 of a brachial disorder, 6 of mental defect, and 8 of an absent pectoral muscle. Thus the overlap with other neuromuscular and CNS abnormalities is evident. Moreover, at least two configurations of brainstem dysfunction have been proposed, one because of a lack of the facial nerve nucleus and the other in the nerve, perhaps acquired in type, based on electrophysiologic studies, but we have no basis to judge the validity of this. Harriëtte and coworkers emphasize the frequency of hypoplastic or dysplastic tongue, palatal involvement, and general motor clumsiness. They suggest that the disorder represents a widespread form of brainstem maldevelopment.
Early in life the mouth hangs open, the lower lip is everted, and there is difficulty in sucking. Usually this syndrome can be distinguished from the facial palsy of forceps or birth injury by its bilaterality and the other associated weaknesses. Occasionally, more than one family member is affected (usually in a pattern suggesting autosomal dominant inheritance). The cause of this peculiar condition is not known. The few adequate pathologic studies have shown a paucity of nerve cells in the motor nuclei of the brainstem, changes that also characterize the Fazio-Londe type of muscular dystrophy discussed in Chap. 45. Rarely, there may be an aplasia of facial muscles. The Möbius syndrome is also referred to in Chap. 44 in relation to restricted palsies of myopathic and nuclear origin.
Partial paralysis of facial muscles that dates from birth and cannot be attributed to obstetric trauma is not infrequent. In a common type, the lower lip on one side remains immobile when the child smiles or cries; the lip on the unaffected side is drawn downward and outward, resulting in a prominent asymmetry of the lower face. Often it is not appreciated that the side that droops during crying is the normal side (Hoefnagel and Penry).
Congenital Lack of Lateral Gaze