Marcus Gunn phenomenon
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![An afflicted young woman demonstrating The Marcus Gunn Jaw Wink Phenomenon. The woman cannot control her eyelids while drinking. This is a particularly mild case.](/Images/godic/202501/16/Markusgunjawwinkwoman3312.jpg")
Marcus Gunn phenomenon, also known as Marcus Gunn jaw-winking or trigemino-oculomotor synkinesis, is an autosomal dominant condition with incomplete penetrance, in which nursing infants will have rhythmic upward jerking of their upper eyelid. This condition is characterized as a synkinesis: when two or more muscles that are independently innervated have either simultaneous or coordinated movements.