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Marcus-Gunn syndrome is characterised by ptosis associated with maxillopalpebral synkinesis.
The syndrome is responsible for 5% of congenital ptoses.
The ptosis is corrected by the opening of the mouth or lateral movements of the lower jaw. This may be due to aberrant innervation of the levator muscle by a branch of the nervus trigeminus.
Inverse Marcus Gunn phenomenon and Marin-Amat syndrome present as eyelid drooping on jaw opening. The first is a congenital condition in which the eyelid levator muscle is inhibited, while Marin-Amat syndrome occurs after facial paralysis and is not associated with impairment of orbicularis oculi and levator muscle function.
The syndrome is generally unilateral and sporadic, but bilateral and familial cases with autosomal dominant transmission have been reported.