Marcus-Gunn syndrome (ORPHA:91412)
A rare ophthalmic disorder characterized by congenital ptosis associated with pterygoid-levator synkinesis (also called jaw-winking).
Epidemiology
The syndrome is responsible for 2-6% of congenital ptoses.
Clinical description
Severity of the ptosis and jaw-winking is highly variable. The ptosis is corrected by the opening of the mouth or lateral movements of the lower jaw. The synkinesis can be linked with Duane retraction syndrome and other various strabismus patterns. Amblyopia is also a frequent association. Anisometropia is occasionally reported.
Etiology
The etiology is still unclear and two main hypotheses have been proposed. The first hypothesis suggests the presence of an aberrant connection between the mandibular division of the trigeminal nerve and the oculomotor nerve, possibly provoked in utero. An ephaptic mechanism has been postulated: it would be a persistent phenomenon, determining a stereotyped, well reproducible, and stable movement. The second hypothesis proposes the unmasking of a primitive pathway, due to a neural misdirection in the brainstem, and an electric stimulus of the ipsilateral pterygoid nerve is known to determine a retraction of the upper eyelid in 20% of normal subjects.
Diagnostic methods
Diagnosis is made based on clinical presentation.
Differential diagnosis
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 represents patients with a connection between the orbicularis oculi and not with levator muscle.
Genetic counseling
Marcus-Gunn syndrome is mainly sporadic, although familial cases with an irregular autosomal dominant inheritance have been reported.
Management and treatment
If only mild ptosis and mild jaw winking are present, no intervention is recommended. A moderate ptosis can be corrected with levator muscle advancement, but results in worsening of the aberrant movement. Candidates for this surgery are young adults with moderate ptosis that have learned how to minimize abnormal movements and can control mild synkinesis. Levator resection appears to be inadequate to correct severe ptosis (with high rates of ptosis recurrence) despite a good levator function and should not be performed. If there is severe ptosis and severe jaw-winking, levator excision associated with frontalis suspension or frontalis flap is the treatment of choice. Bilateral treatment yields more satisfactory cosmetic results. Unilateral treatment should be limited to patients with associated anomalies of the affected eye whom are reluctant to accept bilateral procedures.
Prognosis
Prognosis is usually good if an adequate treatment is planned. Occasionally, ptosis seems to improve with time, although there is no evidence that this really happens. A possibility is that, as time passes, the patient recognizes which movements are responsible for the synkinesis and learns how to control it.

                            Last update: 
                            May 2024


                            - Expert reviewer(s): 
                            Pr Francesco QUARANTA LEONI