In some families the condition is associated with variants in the Chimerin 1 gene and in others it is associated with variants in the Transcription factor MafB gene. Diagnosis
Classification
Duanes syndrome has three variants:

Type I: Limited abduction with or without esotropia
Type II: Limited adduction with or without exotropia
Type III: Limitation of both abduction and adduction and any form of horizontal strabismusBrown(1950) has classified Duanes syndrome according to the characteristics of the limitation of movement-

Type A: with limited abduction and less-marked limitation of adduction
Type B: showing limited abduction but normal adduction
Type C: the limitation of adduction exceeds the limitation of abduction. There is an exotropic deviation and a head turn to compensate the loss of adductionThe first type is more common and accounts for 85% of the cases. Differential diagnosis
In the clinical setting, the principal difficulties in differential diagnosis arise as a consequence of the very early age at which patients with this condition first present. The clinician must be persistent in examining abduction and adduction, and in looking for any associated palpebral fissure changes or head postures, when attempting to determine whether what often presents as a common childhood squint (note-"squint" is a British term for two eyes not looking in the same direction) is in fact Duane syndrome. Fissure changes, and the other associated characteristics of Duanes such as up or down shoots and globe retraction, are also vital when deciding whether any abduction limitation is the result of Duanes and not a consequence of VI or abducens cranial nerve palsy.
Alexandrakis and Saunders found that in most cases the abducens nucleus and nerve are absent or hypoplastic, and the lateral rectus muscle is innervated by a branch of the oculomotor nerve. This view is supported by the earlier work of Hotchkiss et al. who reported on the autopsy findings of two patients with Duanes syndrome. In both cases the sixth cranial nerve nucleus and nerve was absent, and the lateral rectus muscle was innervated by the inferior division of the third or oculomotor nerve. This misdirection of nerve fibres results in opposing muscles being innervated by the same nerve. Thus, on attempted abduction, stimulation of the lateral rectus via the oculomotor nerve will be accompanied by stimulation of the opposing medial rectus via the same nerve; a muscle which works to adduct the eye. Thus, co-contraction of the muscles takes place, limiting the amount of movement achievable and also resulting in retraction of the eye into the socket. They also noticed mechanical factors and considered them secondary to loss of innervation: During corrective surgery fibrous attachments have been found connecting the horizontal recti and the orbital walls and fibrosis of the lateral rectus has been confirmed by biopsy. This fibrosis can result in the lateral rectus being tight and acting as a tether or leash. Co-contraction of the medial and lateral recti allows the globe to slip up or down under the tight lateral rectus producing the up and down shoots characteristic of the condition. Genetics
There are two known genetic associations with Duane Syndrome.