Marcus Gunn syndrome is a rare congenital trigemino-oculomotor synkinesis, also called Marcus Gunn jaw-winking syndrome, jaw-winking ptosis, or maxillopalpebral synkinesis. The synchronization of two independent facial movements links the eyelid movement of one eye with jaw movement, so that as the jaw moves, the upper eyelid appears to wink. It may occur sporadically, but it is believed to be familial (autosomal dominant inheritance) in about 50% of cases. It is often seen in infants with blepharoptosis, sometimes associated with strabismus or other visual problems. Males and females are equally affected, and it is usually present at birth. Typically only one eye is affected, although there are rare cases of bilateral Marcus Gunn syndrome.
It is most recognizable when the half-closed superior eyelid suddenly opens with sucking, chewing, smiling, or another jaw and facial movement.
Marcus Gunn phenomenon may be related to innervation dysfunction originating during fetal development. It is hypothesized that the disorder is due to aberrant connection between the motor branch of the trigeminal nerve and the oculomotor nerve.