APR 25, 2019
This paper examines the pathogenesis of congenital oculonasal synkinesis in a pediatric patient and discusses the implications of disparate craniofacial findings.
This case study describes a 4-year-old girl with maxillary hypoplasia, intermittent exotropia and high myopia who displayed congenital oculonasal synkinesis.
The authors propose that the findings might stem from a variation in the expression of protein-coding genes and signal proteins needed to guide axon development and scleral and bone growth. Specifically, aberrations in neurogenesis could account for the finding of congenital oculonasal synkinesis in association with high myopia, maxillary hypoplasia and intermittent exotropia.
Congenital oculonasal synkinesis is a rare condition that is often asymptomatic. The authors explain that the condition may result from misdirection of cranial nerve axon growth in utero or from acquired compression/trauma, leading to a common innervation by the facial nerve to the orbicularis oculi and the compressor narium minor. The orbicularis oculi is a broad flat muscle arranged in concentric bands around the upper and lower eyelids, and is innervated by the temporal and zygomatic branches of the facial nerve. The compressor narium minor muscle is a small, pyramidal muscle oriented across the domes of the lower lateral cartilages, innervated by the superior buccal branches of the facial nerve. The musculus dilator naris anterior (apices nasi) and the musculus compressor narium minor are in close apposition to the lower lateral cartilages and play an important role in compressing the alae.
Case series are inherently limited by the availability of patients with rare conditions.
The authors examine the implications for the pathogenesis of these disparate craniofacial findings. Misdirection of facial nerve growth may be explained by a lack of function of NRP1 and semaphorins. A decreased expression of these proteins could lead to a decrease in the levels of vascular endothelial growth factor, resulting in delayed formation of bone and increased avascular zones within the sclera, and resulting in high myopia and maxillary hypoplasia seen in the patient. Additional studies are needed to confirm this association.