A novel de novo KIF21A mutation in a patient with congenital fibrosis of the extraocular muscles and möbius syndrome

Purpose: To describe the phenotypic characteristics and clinical course of a sporadic case of congenital fibrosis of the extraocular muscles (CFEOM) and Möbius syndrome with a de novo mutation in the KIF21A gene encoding a kinesin motor protein. Methods: An individual with the rare combination of CFEOM and Möbius syndrome underwent comprehensive ophthalmologic and neurological evaluations. Magnetic resonance imaging (MRI) including diffusion tensor imaging (DTI) tractigraphy at 3T field strength was used to evaluate orbital, encephalic, and intracranial nerve integrity. The proband and her healthy parents underwent screening for mutations in the KIF21A, PHOX2A, and TUBB3 genes. Results: The patient exhibited congenital, nonprogressive, bilateral external ophthalmoplegia, bilateral ptosis, bilateral facial palsy, and developmental delay. Her inability to blink resulted in severe exposure keratopathy and subsequent corneal perforation requiring a penetrating keratoplasty. MRI revealed an unremarkable configuration of the axial central nervous system and preservation of the intracranial portion of cranial nerves I, II, III, V, VI, VII, and VIII (cranial nerve IV is not normally visualized by MRI). A novel and de novo heterozygous KIF21A mutation (c.1056C>G, p.Asp352Glu) in a highly conserved region of the gene was present in the proband. Conclusions: The reported KIF21A D352E mutation and associated phenotype further expand the clinical and mutational spectrum of CFEOM and Möbius syndrome.