A rare case of congenital fibrosis of extraocular muscle type 1A due to KIF21A mutation with Marcus Gunn jaw-winking phenomenon

• Congenital fibrosis of the extraocular muscles (CFEOM) is a rare syndrome characterized by congenital restrictive ophthalmoplegia.
• We describe the clinical and genetic findings in a pediatric patient with CFEOM and Marcus Gunn jaw-winking phenomenon (MG).
• Mutations in KIF21A have been shown to cause CFEOM1, and several authors have reported the coexistence of CFEOM1 and MG.
• The aberrant innervation between developing cranial nerves suggests a role for KIF21A in axonal development.

BackgroundCongenital fibrosis of the extraocular muscles (CFEOM1) is classically a congenital, non-progressive, restrictive strabismus syndrome characterized by bilateral ptosis and ophthalmoplegia with an infraducted position of the globes. This autosomal dominant syndrome is caused by mutations in the KIF21A gene.Methods and resultsIn this report we describe a 5-year-old boy, and his mother, both of whom have a mutation in the KIF21A gene, who possesses typical features of CFEOM1 syndrome. Besides displaying typical features of CFEOM1, he demonstrated Marcus Gunn jaw-winking phenomenon. The patient additionally had a positive family history of such features.ConclusionThis is first report of the coexistence of CFEOM and Marcus Gunn jaw-winking phenomenon in a patient with a KIF21A mutation from Turkey. We explain the phenotypic findings associated with mutations in KIF21A including CFEOM1A and Marcus Gunn jaw-winking phenomenon.