Marcus Gunn phenomenon is an

autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

condition with

incomplete penetrance Penetrance in genetics is the proportion of individuals carrying a particular variant (or allele) of a gene (the genotype) that also express an associated trait (the phenotype). In medical genetics, the penetrance of a disease-causing mutation is t ...

, in which nursing infants will have rhythmic upward jerking of their upper eyelid. This condition is characterized as a

synkinesis Synkinesis is a neurological symptom in which a voluntary muscle movement causes the simultaneous involuntary contraction of other muscles. An example might be smiling inducing an involuntary contraction of the eye muscles, causing a person to squ ...

: when two or more muscles that are independently innervated have either simultaneous or coordinated movements. Common physiologic examples of synkineses occur during sucking, chewing, or conjugate eye movements. There are also several abnormal

cranial nerve Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and ...

synkineses, both acquired and congenital. Marcus Gunn jaw-winking is an example of a pathologic congenital synkinesis. First described by the ophthalmologist

Marcus Gunn Robert Marcus Gunn (1850, Dunnet – 29 November 1909, Hindhead) was a Scottish ophthalmologist remembered for Gunn's sign and the Marcus Gunn pupil. Early life and education Gunn went to school in Golspie, then studied medicine at th ...

in 1883,Gunn RM. Congenital ptosis with peculiar associated movements of the affected lid. Trans Ophthal Soc UK. 1883;3:283-7. this condition presents in approximately 5% of neonates with congenital ptosis. This condition has been associated with

amblyopia Amblyopia, also called lazy eye, is a disorder of sight in which the brain fails to fully process input from one eye and over time favors the other eye. It results in decreased vision in an eye that typically appears normal in other aspects. Amb ...

(in 54% of cases),

anisometropia Anisometropia refers to a condition when two eyes have unequal refractive power. Generally, a difference in power of one diopter (1D) or more is the accepted threshold to label the condition anisometropia. Patients can tolerate 3 D of anisometro ...

(26%), and

strabismus Strabismus is a vision disorder in which the eyes do not properly align with each other when looking at an object. The eye that is focused on an object can alternate. The condition may be present occasionally or constantly. If present during a ...

(56%).

Presentation

Behavioral and social implications

Although treatment may be unnecessary, there may be social implications, especially in young children when venturing from a supportive home environment to a public environment (e.g., starting school). Continued support, including monitoring behavior and educating the child about his or her appearance as seen by others, is encouraged. Gradual or sudden withdrawal from interaction with others is a sign that may or may not be related to such behavior. Studies are being conducted to elucidate these implications.

Pathophysiology

It has been postulated that the synkinesis is due to damage to cranial nerve nuclei, caused by peripheral nerve injury and the nuclear lesion releases evolutionarily older

eural Eural may refer to: * Eural Trans Gas, a Hungarian energy company * Eural, a Belgian bank, subsidiary of Dexia Dexia N.V./S.A., or the Dexia Group, is a Franco-Belgian financial institution formed in 1996. At its peak in 2010, it had about 35, ...

mechanisms with their tendency toward associated movements, and so primitive reflexes are not inhibited. Marcus Gunn jaw-winking is an exaggeration of a very weak physiologic co-contraction that has been disinhibited secondary to a congenital brain stem lesion. The stimulation of the trigeminal nerve by contraction of the pterygoid muscles of jaw results in the excitation of the branch of the oculomotor nerve that innervates the levator palpebrae superioris ipsilaterally (on the same side of the face), so the patient will have rhythmic upward jerking of their upper eyelid. There are two major groups of trigemino-oculomotor synkineses:
1) External pterygoid-levator synkinesis is when the eyelid raises upon: * Jaw thrust to opposite side (homolateral external pterygoid) * Jaw is projected forward (bilateral external pterygoid) * Mouth is opened widely 2) Internal pterygoid-levator synkinesis is when the eyelid raises upon teeth clenching External pterygoid-levator synkinesis is the more common group.

Treatment

Treatment is usually unnecessary. In severe cases, surgery with a bilateral levator excision and frontalis brow suspension may be used.

Inverse Marcus Gunn phenomenon

Inverse Marcus Gunn phenomenon is a rare condition that causes the eyelid to fall upon opening of the mouth. In this case, trigeminal innervation to the pterygoid muscles of the jaw is associated with an inhibition of the branch of the oculomotor nerve to the levator palpebrae superioris, as opposed to stimulation in Marcus Gunn jaw-winking.

References

External links

{{DEFAULTSORT:Marcus Gunn Phenomenon Congenital disorders of eyes Congenital disorders of nervous system