Congenital Fibrosis of the Extraocular Muscles

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Main Features

Non-progressive hereditary strabismus syndrome belonging to the congenital cranial dysinnervation disorders (CCDDs), characterized by congenital restrictive ophthalmoplegia with or without ptosis.
Prevalence ~1/250,000–1/230,000
Maldevelopment of the oculomotor (CN III) and trochlear (CN IV) nuclei/nerves and their axons, with secondary changes in the innervated muscles. This leads to a secondary fibrosis.

Congenital non-progressive external ophthalmoplegia with severe limitation of vertical gaze (usually upgaze) and variable limitation of horizontal gaze.

Fixed infraduction (eyes fixed downward) in classic CFEOM1; CFEOM2 characteristically shows bilateral large-angle exotropia; CFEOM3 often unilateral/asymmetric involvement.

Ptosis (uni- or bilateral) from levator palpebrae superioris dysfunction, with compensatory chin-up head posture to see beneath the lids and better position the infraducted eyes.

Incomitant strabismus (hypotropic/exotropic positions more common), absent binocular vision/poor stereopsis, refractive errors, amblyopia, and poor visual acuity.

Aberrant eye movements (e.g., convergent movement on attempted upgaze) and, in CFEOM2, poorly reactive pupils (pupillary involvement is absent in CFEOM1).

Neuroimaging (MRI): hypoplasia of extraocular muscles and hypoplastic oculomotor nerves; trochlear, abducens, and optic nerves may also be hypoplastic.

Predominantly in CFEOM3, syndromic non-ocular features may occur: facial paralysis and dysmorphism, vocal cord paralysis, intellectual/social disability, Kallmann syndrome (hypogonadotropic hypogonadism with anosmia), progressive peripheral sensorimotor axonal polyneuropathy, congenital joint contractures, gait anomalies, cyclic vomiting, and epilepsy.

Microcephaly and intellectual disability, particularly in CFEOM3 with polymicrogyria.

Marcus Gunn jaw-winking phenomenon and other signs of aberrant dysinnervation, supporting a neurogenic etiology.

Tukel syndrome: bilateral postaxial oligodactyly/oligosyndactyly of the hands.

CFEOM has also been reported with progressive cerebellar ataxia and, via COL25A1 variants, with arthrogryposis multiplex congenita.

A congenital cranial dysinnervation disorder caused by abnormal development of ocular motor neurons and their axons, altering either motor neuron specification or nerve growth/guidance.

CFEOM1: heterozygous KIF21A mutations (chromosome 12q12; kinesin motor protein affecting axonal transport) — autosomal dominant.
CFEOM2: homozygous PHOX2A/ARIX mutations (11q13; homeodomain transcription factor required for CN III/IV development) — autosomal recessive.
CFEOM3: KIF21A or β-/α-tubulin isotype genes TUBB3 (16q24), TUBB2B (6p25), or TUBA1A — autosomal dominant, with variable expressivity.
- Tukel syndrome is CFEOM3 with ulnar hand anomalies.

Germline mosaicism is common in apparently sporadic CFEOM1 (presumed rate ~38%), which can mimic recessive inheritance and is important for genetic counseling.

Feature	CPEO	CFEOM
Nature of disorder	Mitochondrial myopathy of extraocular muscle	Congenital cranial dysinnervation disorder (neurogenic; abnormal CN III/IV/VI development with secondary muscle fibrosis)
Onset	Adult, typically 18–40 yrs; ptosis first sign	Congenital / present at birth
Course	Slowly progressive over years	Non-progressive (rare exceptions)
Symmetry / gaze	Generally symmetric, diffuse limitation of all directions; superior rectus often prominently involved	Fixed characteristic pattern — CFEOM1: eyes fixed in infraduction, absent upgaze; CFEOM2: large-angle exotropia
Ptosis	Common, may be uni- or bilateral, progressive	Congenital, typically bilateral; chin-up head posture
Diplopia	Usually absent (<30%) due to gradual symmetric onset	Absent; binocular vision typically never develops
Pupils	Spared	Spared in CFEOM1; poorly reactive in CFEOM2
Inheritance / genetics	Single large-scale mtDNA deletion (~50%, sporadic); also nuclear mtDNA-maintenance genes (POLG, RRM2B, TWNK) and mtDNA point mutations	Mendelian: CFEOM1 (AD, KIF21A); CFEOM2 (AR, PHOX2A); CFEOM3 (AD, TUBB3/TUBB2B/TUBA1A/KIF21A)
Systemic/associated features	“CPEO-plus”: retinopathy, ataxia, neuropathy, deafness, cardiac conduction block, diabetes (Kearns-Sayre)	Usually isolated; CFEOM3 may have developmental/CNS anomalies (e.g., Tukel syndrome)
Muscle biopsy	Ragged-red / COX-negative fibers; mitochondrial abnormalities	Not a mitochondrial biopsy diagnosis; muscle shows fibrosis/denervation changes
Orbital MRI	Mild EOM atrophy with fatty/spongiform T1 signal	EOM hypoplasia + hypoplastic ocular motor nerves