KIF21A

Fibrosis of Extraocular Muscles, CFEOM1

Clinical Characteristics
Ocular Features: 

Hereditary CFEOM is a congenital, nonprogressive condition.  The eyes are usually fixed in the infraducted position about 20-30 degrees below the primary position.  Horizontal movement is absent or severely restricted.  Blepharoptosis is almost always present and patients exhibit a marked chin-up position of gaze.  Binocularity is usually absent.  Some patients have large amounts of astigmatism.  Amblyopia has been reported to occur on a refractive or strabismic basis.  However, careful examination of the optic nerve may reveal anomalies such as increased cupping, asymmetric cupping and hypoplasia and could be responsible for the reduced vision in some patients.

Neuropathologic studies in rare patients have shown defects in brainstem neural development including in one case absence of the superior division of the oculomotor nerve.  Fibrosis of extraocular muscles and Tenon's capsule as well as adhesions to the globe and between muscles have been described.   Anomalous insertions of EOMs may also occur.  An MRI can reveal atrophy of the levator palpebrae and the superior rectus muscles as well as absence or hypoplasia of the oculomotor and sometimes abducens nerves.  It is now considered that CFEOM disorders result from primary neuronal disease resulting in secondary myopathy. 

Systemic Features: 

Late onset gait abnormalities associated with MRI documented vermis atrophy have been reported in a single autosomal dominant pedigree.  The diagnosis of CFEOM1 was confirmed with molecular studies but only two older individuals aged 79 and 53 years had the cerebellar atrophy while a 33 year old in the same family had only CFEOM with no gait difficulties and no neuroimaging abnormalities.

Genetics

CFEOM1 is an autosomal dominant disorder caused by mutations in the KIF21A gene located at 12q12.  This is considered the classic form of congenital, restrictive strabismus but other types such as CFEOM2 (602078) and CFEOM3 (600638, 609384) have also been reported.  CFEOM3 is a clinically heterogeneous autosomal dominant condition and the label is usually applied to individuals who do not meet the criteria for the other two types.  A rare subtype (CFEOM3B) is also due to mutations in the KIF21A gene.  CFEOM3A (600638) is caused by mutations in the TUBB3 gene (16q24) while CFEOM3C (609384) maps to 13q.

The CFEOM2 (602078) phenotype is due to mutations in the PHOX2A (ARIX) gene and inherited in an autosomal recessive pattern.

Other nonsyndromal forms of congenital fibrosis of extraocular muscles include: CFEOM3C (609384), CFEOM5 (616219), and CFEOM with synergistic divergence (609612).  See also Tukel CFEOM syndrome (609428).

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

Normal ocular movements cannot be restored but large recessions of the inferior recti followed by frontalis suspension of the upper eyelids can improve severe ptosis and the compensatory chin-up gaze. Corneal lubrication must be maintained.  Refractive errors and amblyopia should be corrected.  

References
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