Duane retraction syndrome is a clinically and genetically heterogeneous condition with a highly variable phenotype. It is a congenital and non-progressive strabismus syndrome. Most cases occur sporadically but others are familial and about 30% of affected individuals have other congenital anomalies. It is also seen as part of other syndromes such as Goldenhar (164210), and Wildervanck (314600). In the absence of other anomalies, it is called isolated Duane syndrome. Three heritable types with autosomal dominant familial patterns have also been defined. Patients with type 2 discussed here are more likely to have an exotropia with a head turn toward the uninvolved side when only one eye is involved compared with Duane syndrome type 1 (126800) in which an esotropia with a head turn to the involved side is more common. However, the clinical features are highly variable although intrafamilial differences may be less than those between families.
Sporadic cases are mostly unilateral while familial ones are more likely to be bilateral. The essential features are globe retraction upon adduction with narrowing of the lid fissure and some limitation of abduction. Vertical deviation during adduction is sometimes seen. Frank strabismus in primary position is evident in as many as 76% of individuals and a compensatory head turn is often adopted. Still, amblyopia occurs in at least 10% of individuals. Females are affected more frequently than males.
At one point the syndrome was considered to be a myopathic disorder based on histologic changes in the lateral rectus but current thought based on MRI and neurohistologic studies favors a neuropathic etiology. The abducens motor neurons and the sixth nerve may be absent or dysplastic. Branches of the third nerve may also co-innervate the lateral and medial rectus muscles. EMG studies have documented simultaneous activation of the two muscles which likely accounts for at least some of the globe retraction. However, hypoplastic muscles, including the superior oblique, superior rectus, and levator, have also been visualized on MRI.