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Inheritance

2

Autosomal dominant inheritance HP:0000006

CFEOM1 and CFEOM3 (KIF21A, TUBB3, TUBB2B) are inherited in an autosomal dominant manner; affected individuals are heterozygous for a missense variant.

Autosomal dominant inheritance

Show evidence (2 references)

PMID:14595441 SUPPORT Human Clinical

"Congenital fibrosis of the extraocular muscles type 1 (CFEOM1; OMIM #135700) is an autosomal dominant strabismus disorder associated with defects of the oculomotor nerve."

Establishes CFEOM1, the commonest form, as an autosomal dominant disorder of the oculomotor nerve.

PMID:20074521 SUPPORT Human Clinical

"We report that eight heterozygous missense mutations in TUBB3, encoding the neuron-specific beta-tubulin isotype III, result in a spectrum of human nervous system disorders that we now call the TUBB3 syndromes."

Heterozygous TUBB3 missense variants are sufficient to cause CFEOM3, supporting autosomal dominant transmission of that subtype.

Autosomal recessive inheritance HP:0000007

CFEOM2 (PHOX2A/ARIX), CFEOM5 (COL25A1), and the Tukel syndrome variant are inherited in an autosomal recessive manner, and have been described mainly in consanguineous families.

Autosomal recessive inheritance

Show evidence (2 references)

PMID:14597037 SUPPORT Human Clinical

"Both parents and the unaffected siblings were heterozygous,and the two affected siblings were homozygous for this mutation."

Homozygous affected siblings with heterozygous unaffected parents establishes autosomal recessive transmission of CFEOM2.

PMID:25500261 SUPPORT Human Clinical

"we identified three mutations in collagen, type XXV, alpha 1 (COL25A1) in individuals with autosomal-recessive inheritance of CCDD ophthalmic phenotypes."

Establishes autosomal recessive inheritance for the COL25A1 (CFEOM5) form.

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Subtypes

7

CFEOM1 (KIF21A, classic bilateral CFEOM) MONDO:0021083

KIF21A hgnc:19349

The classic and most common form. Autosomal dominant, fully penetrant, and bilateral: both eyes are fixed in a downward (infraducted) position with severe bilateral ptosis and inability to elevate either eye above the horizontal midline. Caused by heterozygous missense variants in the kinesin KIF21A, with recurrent hotspots in the third coiled-coil stalk domain (p.R954W is by far the commonest allele, recurring across ancestries).

Show evidence (2 references)

PMID:14595441 SUPPORT Human Clinical

"We show that individuals with CFEOM1 harbor heterozygous missense mutations in a kinesin motor protein encoded by KIF21A. We identified six different mutations in 44 of 45 probands."

Establishes heterozygous KIF21A missense variants as the cause of CFEOM1 in nearly all probands tested.

PMID:16365788 SUPPORT Human Clinical

"Clinically, each patient had congenital bilateral ptosis, an infraducted primary position of each eye, and the inability to raise either eye above midline."

Defines the stereotyped bilateral CFEOM1 clinical picture in KIF21A p.R954W carriers.

CFEOM2 (PHOX2A/ARIX, autosomal recessive) MONDO:0011181

PHOX2A hgnc:691

Autosomal recessive form, described mainly in consanguineous Middle Eastern families. Affected individuals have bilateral ptosis with the eyes fixed in an exotropic (outward) rather than infraducted position and severe limitation of all extraocular movements. Caused by biallelic loss of PHOX2A/ARIX, a homeodomain transcription factor required for specification of the oculomotor and trochlear motor nuclei.

Show evidence (2 references)

PMID:11600883 SUPPORT Human Clinical

"Here, we report three mutations in ARIX (also known as PHOX2A) in four CFEOM2 pedigrees."

Identifies PHOX2A/ARIX as the CFEOM2 disease gene across four pedigrees.

PMID:14597037 SUPPORT Human Clinical

"The two affected siblings had bilateral ptosis and exotropia and severe limitation of all extraocular movements."

Documents the distinguishing exotropic primary position of CFEOM2.

CFEOM3A (TUBB3, with or without extraocular involvement) MONDO:0010912

TUBB3 hgnc:20772

Autosomal dominant, more variable and often asymmetric or unilateral form caused by heterozygous missense variants in TUBB3, the neuron-specific beta-tubulin isotype III. Unlike CFEOM1, the eyes are not always infraducted and one eye may be spared. Some TUBB3 alleles add extraocular features - intellectual and behavioural impairment, facial weakness, and a later-onset axonal sensorimotor polyneuropathy - together with commissural and corticospinal tract dysgenesis on neuroimaging. See the separate TUBB3-related Tubulinopathy entry for the wider TUBB3 syndrome spectrum.

Show evidence (1 reference)

PMID:20074521 SUPPORT Human Clinical

"Each mutation causes the ocular motility disorder CFEOM3, whereas some also result in intellectual and behavioral impairments, facial paralysis, and/or later-onset axonal sensorimotor polyneuropathy."

Defines CFEOM3 as the constant ocular phenotype of TUBB3 missense variants with variable additional neurological features.

CFEOM3B (KIF21A) MONDO:0800209

KIF21A hgnc:19349

A CFEOM3-pattern (variable, potentially unilateral or asymmetric, eyes not obligately infraducted) phenotype caused by KIF21A variants rather than TUBB3, showing that the same KIF21A allele can produce either the classic CFEOM1 pattern or a CFEOM3 pattern within and between families.

Show evidence (1 reference)

PMID:27513105 SUPPORT Human Clinical

"The results indicated that, in the patients with CFEOM1 and CFEOM3, the disease was caused by the same KIF21A gene mutation."

Demonstrates that a single recurrent KIF21A allele underlies both the CFEOM1 and CFEOM3 clinical patterns.

CFEOM3C (13q12.11-linked) MONDO:0012262

A locus-defined CFEOM3 subtype mapped by linkage in a family without a KIF21A or TUBB3 variant. It is retained here as a distinct nosological entity because the causal gene at the locus is not established, so the subtype cannot yet be folded into a gene-defined class.

CFEOM5 (COL25A1, autosomal recessive) MONDO:0014538

COL25A1 hgnc:18603

Autosomal recessive CCDD with a CFEOM ophthalmic phenotype caused by biallelic COL25A1 variants that reduce protein stability or level. COL25A1 encodes CLAC-P, a transmembrane collagen implicated in oculomotor neuron development, placing this subtype outside the cytoskeletal and transcription-factor mechanisms of the other subtypes.

Show evidence (1 reference)

PMID:25500261 SUPPORT Human Clinical

"Our data suggest that lack of COL25A1 might interfere with molecular pathways involved in oculomotor neuron development, leading to CCDD phenotypes."

Assigns the COL25A1 subtype to the same oculomotor-neuron developmental mechanism as the rest of the CFEOM spectrum.

Tukel syndrome (CFEOM with postaxial ulnar hand anomalies) MONDO:0012270

An autosomal recessive syndromic variant in which non-progressive restrictive ophthalmoplegia with blepharoptosis is accompanied by postaxial (ulnar) oligodactyly or oligosyndactyly of the hands. Described in a large consanguineous Turkish family and mapped by linkage to chromosome 21qter; the causal gene remains unidentified. The co-occurrence of a cranial dysinnervation phenotype with a posterior limb-patterning defect is the feature that distinguishes it from isolated CFEOM.

Show evidence (2 references)

PMID:15863670 SUPPORT Human Clinical

"The postaxial oligodactyly/oligosyndactyly of the hands was more severe on the right side."

Defines the ulnar hand anomaly that distinguishes Tukel syndrome from isolated CFEOM.

PMID:15863670 SUPPORT Human Clinical

"A genome-wide scan established linkage of this new autosomal recessive syndrome to a locus on chromosome 21qter."

Establishes the recessive inheritance and 21qter locus of Tukel syndrome.

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Discussions and Knowledge Gaps

3

Why do ubiquitously expressed lesions in KIF21A, TUBB3, TUBB2B, and COL25A1 produce a phenotype largely restricted to the oculomotor and trochlear nerves rather than a generalised axonopathy?

KNOWLEDGE GAP OPEN gap_cfeom_selective_oculomotor_vulnerability

Attached to

pathophysiology#KIF21A Kinesin Autoinhibition Loss pathophysiology#Beta-Tubulin Microtubule Dysfunction in Cranial Motor Neurons pathophysiology#Oculomotor Axon Stalling and Aberrant Growth Cone Guidance

KIF21A and the beta-tubulins are expressed far more widely than the ocular motor nuclei, yet CFEOM1 is a clinically isolated eye movement disorder. The mouse work names this as a selective vulnerability of the developing oculomotor nerve to cytoskeletal perturbation but does not explain what confers it, and the TUBB3 alleles that do add extraocular features show the restriction is allele-dependent rather than absolute. Without a mechanism for the selectivity, genotype-phenotype prediction across the spectrum remains descriptive.

Proposed experiments

Developmental-stage profiling of ocular motor versus spinal motor neurons

exp_cfeom_ocular_motor_neuron_specific_profiling

Compare the transcriptome, cytoskeletal composition, and kinesin cargo complement of developing oculomotor, trochlear, abducens, and spinal motor neurons at the stage at which CFEOM axons stall, in wild-type and in Kif21a and Tubb3 knockin animals, to identify features that distinguish the vulnerable from the spared pools.

Decision criterion

Identification of a factor whose loss or supplementation shifts the stalling phenotype between ocular motor and spared motor neuron populations.

Would support

pathophysiology#Oculomotor Axon Stalling and Aberrant Growth Cone Guidance

Show evidence (2 references)

PMID:24656932 SUPPORT Model Organism

"highlights a selective vulnerability of the developing oculomotor nerve to perturbations of the axon cytoskeleton"

Names the selective vulnerability that this gap asks to be explained.

PMID:34081534 SUPPORT Human Clinical

"Study of these disorders highlights the complexities of axon guidance and how each population of neurons uses a unique but overlapping set of axon guidance pathways."

Frames the population-specific guidance repertoire that a mechanism for the selectivity would have to explain.

Should CFEOM continue to be classified ontologically as a myopathy of extraocular muscle and a progressive muscular dystrophy when the evidence establishes it as a non-progressive neurogenic dysinnervation disorder?

KNOWLEDGE GAP OPEN gap_cfeom_mondo_myopathy_classification

Attached to

pathophysiology#Hypoplasia of the Oculomotor and Trochlear Nerves pathophysiology#Denervation-Driven Extraocular Muscle Maldevelopment and Fibrosis

MONDO:0007614 is currently placed under both myopathy of extraocular muscle and progressive muscular dystrophy. Human neuropathology and genotyped orbital MRI both establish that the neuronal lesion is primary and the myopathy secondary, and every characterisation of the disorder describes it as non-progressive. The ontology placement therefore asserts two things the curated mechanism contradicts. This entry records the discrepancy rather than silently reclassifying; resolving it belongs upstream in MONDO.

Show evidence (1 reference)

PMID:15671279 SUPPORT Human Clinical

"These findings suggest that neuronal disease is primary in CFEOM1, with myopathy arising secondary to abnormal innervation and minimal rectus pulley abnormality secondary to reduced EOM forces."

States the primary-neurogenic, secondary-myopathic ordering that conflicts with a myopathy or dystrophy classification.

What accounts for the majority of CFEOM and related ocular congenital cranial dysinnervation disorder probands who remain genetically unsolved after exome and genome sequencing?

KNOWLEDGE GAP OPEN gap_cfeom_genetically_unsolved_probands

Attached to

pathophysiology#Oculomotor Axon Stalling and Aberrant Growth Cone Guidance pathophysiology#Hypoplasia of the Oculomotor and Trochlear Nerves

The named CFEOM subtypes account for only part of the clinical spectrum. A large sequencing study of previously unsolved ocular CCDD pedigrees resolved fewer than one in ten probands and left most of the cohort without a pathogenic variant, so the curated gene list here is a floor rather than a complete account of the disorder. The locus-defined CFEOM3C subtype and the unmapped Tukel syndrome gene are the same gap visible from the nosological side.

Proposed experiments

Non-coding and functional replication of prioritized oCCDD candidates

exp_cfeom_noncoding_and_functional_replication

Extend sequencing of unsolved CFEOM pedigrees beyond protein-coding regions to regulatory and structural variation affecting the established axon-guidance genes, and functionally test prioritized candidate variants in ocular motor neuron models for the stalling and misrouting phenotype.

Decision criterion

Replication of a candidate gene or regulatory variant in independent pedigrees together with a reproducible ocular motor axon phenotype in a model system.

Would support

pathophysiology#Oculomotor Axon Stalling and Aberrant Growth Cone Guidance

Show evidence (2 references)

PMID:39033378 SUPPORT Human Clinical

"Analyses elucidated phenotypic subgroups, identified pathogenic/likely pathogenic variant(s) in 43 of 467 probands (9.2%), and prioritized variants of uncertain significance in 70 of 467 additional probands (15.0%)."

Quantifies how much of the previously unsolved ocular CCDD cohort remains without an established genetic cause.

PMID:39033378 SUPPORT Human Clinical

"This study suggests that unsolved oCCDDs are clinically and genetically heterogeneous disorders often overlapping other Mendelian conditions and nominates many candidates for future replication and functional studies."

States that the residual cohort is heterogeneous and overlaps other Mendelian conditions, which is why the gap is not closed by one gene.

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Pathophysiology

10

KIF21A Kinesin Autoinhibition Loss

KIF21A is an anterograde kinesin whose motor activity is normally restrained by an intramolecular autoinhibitory interaction between its third coiled-coil stalk and its motor domain. The recurrent CFEOM1 missense variants cluster in exactly these two elements and attenuate that autoinhibition, so the motor is inappropriately active. This is a gain-of-function lesion, not haploinsufficiency, which is why heterozygous missense variants are pathogenic while KIF21A null alleles are not a recognised cause of CFEOM.

oculomotor alpha motor neuron CL:0008038

KIF21A microtubule motor activity GO:0003777 ⇑ GAIN OF FUNCTION

Downstream

Oculomotor Axon Stalling and Aberrant Growth Cone Guidance A disinhibited KIF21A motor perturbs the axonal cytoskeleton of the developing oculomotor nerve, and its superior-division axons fail to advance normally.

Show evidence (2 references)

PMID:24656932 SUPPORT Model Organism

"We establish a gain-of-function mechanism and find that human motor or stalk mutations attenuate Kif21a autoinhibition, providing in vivo evidence for mammalian kinesin autoregulation."

Establishes attenuated KIF21A autoinhibition as the gain-of-function molecular lesion in CFEOM1.

PMID:14595441 SUPPORT Human Clinical

"The primary mutational hotspots are in the stalk domain, highlighting an important new role for KIF21A and its stalk in the formation of the oculomotor axis."

Localises the CFEOM1 variants to the stalk domain that mediates autoinhibition.

PHOX2A-Dependent Oculomotor and Trochlear Nucleus Specification Failure

PHOX2A (ARIX) is a homeodomain transcription factor required to specify the midbrain oculomotor (nIII) and trochlear (nIV) motor nuclei. Biallelic loss-of-function variants remove that determinant, so the motor neuron pools that should innervate the extraocular muscles are never properly formed. This is the CFEOM2 route into the shared downstream lesion, and it is upstream of axon guidance rather than a guidance defect itself.

oculomotor and trochlear alpha motor neuron CL:0008038

oculomotor nerve development GO:0021557 ↓ DECREASED trochlear nerve development GO:0021558 ↓ DECREASED

PHOX2A homeodomain transcription factor activity GO:0003700 ⇓ LOSS OF FUNCTION

Downstream

Hypoplasia of the Oculomotor and Trochlear Nerves Motor nuclei that are never specified cannot send out a normal nerve, so the nIII and nIV trunks are absent or hypoplastic.

Show evidence (3 references)

PMID:11600883 SUPPORT Human Clinical

"ARIX encodes a homeodomain transcription factor protein previously shown to be required for nIII/nIV development in mouse and zebrafish."

Identifies the developmental role of PHOX2A/ARIX in the oculomotor and trochlear nuclei that biallelic loss removes.

PMID:11600883 SUPPORT Human Clinical

"These findings confirm the hypothesis that CFEOM2 results from the abnormal development of nIII/nIV (ref. 7) and emphasize a critical role for ARIX in the development of these midbrain motor nuclei."

Directly attributes CFEOM2 to abnormal development of the nIII/nIV motor nuclei.

PMID:34081534 SUPPORT Human Clinical

"These disorders can arise through one of two mechanisms: (a) defective motor neuron specification, usually by loss of a transcription factor necessary for brainstem patterning, or (b) axon growth and guidance abnormalities of the oculomotor, trochlear, and abducens nerves."

Places the PHOX2A lesion in the transcription-factor specification arm of the two recognised CCDD mechanisms.

Beta-Tubulin Microtubule Dysfunction in Cranial Motor Neurons

TUBB3 and TUBB2B encode neuron-enriched beta-tubulin isotypes that heterodimerise with alpha-tubulin to build the dynamic microtubules of the growing axon and its growth cone. The CFEOM3-causing missense variants impair heterodimer formation, alter microtubule dynamic instability, and in a subset also disrupt the interface through which kinesin motors engage the microtubule lattice. The convergence of this arm with the KIF21A arm on the same clinical phenotype - one lesion in the track, the other in the motor - is the strongest mechanistic argument that CFEOM is a disorder of axonal transport and guidance.

cranial motor neuron CL:0000100

tubulin heterodimer formation GO:0007021 ↓ DECREASED

beta-tubulin structural constituent of the neuronal microtubule GO:0005200 ↕ DYSREGULATED microtubule-kinesin interaction GO:0019894 ↓ DECREASED

Downstream

Oculomotor Axon Stalling and Aberrant Growth Cone Guidance Microtubules whose dynamics and kinesin engagement are perturbed cannot support normal growth-cone steering in the developing ocular motor nerves.

Commissural and Corticospinal Axon Guidance Failure The same tubulin lesion also perturbs guidance of callosal and other long-range projection axons, which is why some TUBB3 and TUBB2B alleles add central nervous system features to the ocular phenotype.

Show evidence (2 references)

PMID:20074521 SUPPORT In Vitro

"Modeling each mutation in yeast tubulin demonstrates that all alter dynamic instability whereas a subset disrupts the interaction of microtubules with kinesin motors."

Establishes altered microtubule dynamics in every allele and disrupted microtubule-kinesin interaction in a subset.

PMID:23001566 SUPPORT In Vitro

"TUBB2B-E421K αβ-heterodimers are incorporated into the microtubule network where they alter microtubule dynamics and can reduce kinesin localization."

Shows the CFEOM-causing TUBB2B allele acts through the same dynamics-and-kinesin mechanism as the TUBB3 alleles.

COL25A1 Loss in Oculomotor Neuron Development

COL25A1 encodes CLAC-P, a neuronal transmembrane collagen. Biallelic variants that reduce its stability or abundance perturb the molecular programme of oculomotor neuron development and alter the levels of axon-guidance-associated proteins including soluble APP and TUBB3 itself, connecting this recessive subtype back to the shared cytoskeletal arm.

oculomotor neuron CL:0000100

oculomotor nerve development GO:0021557 ↓ DECREASED

Downstream

Hypoplasia of the Oculomotor and Trochlear Nerves Loss of COL25A1 interferes with the developmental programme that builds the ocular motor nerves.

Show evidence (1 reference)

PMID:25500261 SUPPORT Human Clinical

"We further detected altered levels of sAPP (neuronal protein involved in axon guidance and synaptogenesis) and TUBB3 (encoded by TUBB3, which is mutated in CFEOM3) as a result of null mutations in COL25A1."

Connects COL25A1 loss to the axon-guidance machinery shared with the other CFEOM subtypes.

Oculomotor Axon Stalling and Aberrant Growth Cone Guidance

The convergent cellular lesion of the cytoskeletal CFEOM subtypes. Axons of the oculomotor nerve, and most consistently those of its superior division that supply the levator palpebrae superioris and superior rectus, stall in the proximal nerve. Their growth cones enlarge, extend excessive filopodia, and take random trajectories instead of following their stereotyped path to the orbit; axons of the inferior division reach the orbit but branch ectopically. This selective vulnerability of the developing oculomotor nerve to perturbations of the axon cytoskeleton is what makes an otherwise ubiquitously expressed motor or tubulin lesion present as an isolated eye movement disorder.

oculomotor alpha motor neuron CL:0008038

motor neuron axon guidance GO:0008045 ↕ DYSREGULATED axon extension of the oculomotor nerve GO:0048675 ↓ DECREASED

Downstream

Hypoplasia of the Oculomotor and Trochlear Nerves Axons that stall or never arrive leave a structurally thin or absent nerve trunk and, over time, loss of the corresponding motor neurons.

Aberrant Reinnervation of Extraocular Muscles Misrouted and ectopically branching oculomotor axons reach muscles they do not normally supply, most characteristically the lateral rectus.

Show evidence (3 references)

PMID:24656932 SUPPORT Model Organism

"Inferior division axons reach the orbit but branch ectopically."

Documents the divergent fate of inferior-division axons alongside the stalled superior division.

PMID:24656932 SUPPORT Model Organism

"highlights a selective vulnerability of the developing oculomotor nerve to perturbations of the axon cytoskeleton"

States the selective vulnerability that explains the restricted phenotype.

PMID:34081534 SUPPORT Human Clinical

"Abnormalities of axon growth and guidance are often limited to a single nerve or subdivision, even when the causative gene is ubiquitously expressed."

Establishes that the guidance defect is restricted to one nerve or nerve subdivision despite ubiquitous expression of the causal gene.

Hypoplasia of the Oculomotor and Trochlear Nerves

The defining structural lesion of CFEOM and the point at which every molecular route converges. Autopsy of a chromosome-12-linked (CFEOM1) family showed absence of the superior division of the oculomotor nerve together with its alpha motor neurons; high-resolution orbital MRI in genotyped KIF21A carriers shows small or absent orbital motor nerves, with the oculomotor nerve most severely hypoplastic and the abducens also affected. The lesion is therefore not confined to nIII, and its extent is wider than the classic superior-division description implies.

oculomotor alpha motor neuron CL:0008038

oculomotor nerve morphogenesis GO:0021622 ↓ DECREASED cranial nerve development GO:0021545 ↓ DECREASED

Downstream

Denervation-Driven Extraocular Muscle Maldevelopment and Fibrosis Extraocular muscles that never receive normal innervation fail to develop and become atrophic and fibrotic - the secondary event that gave the disorder its misleading name.

Show evidence (2 references)

PMID:9066352 SUPPORT Human Clinical

"There is an absence of the superior division of the oculomotor nerve and its corresponding alpha motor neurons, and abnormalities of the levator palpebrae superioris and rectus superior (the muscles innervated by the superior division of the oculomotor nerve)."

Human neuropathology establishes the missing nerve division and motor neuron pool as the primary lesion.

PMID:15671279 SUPPORT Human Clinical

"In affected subjects, MRI demonstrated atrophy of the levator palpebrae superioris and superior rectus EOMs and small or absent orbital motor nerves. The oculomotor nerve was most severely hypoplastic, but the abducens was also affected."

Genotyped in vivo imaging confirms hypoplastic ocular motor nerves and extends the lesion to the abducens.

Denervation-Driven Extraocular Muscle Maldevelopment and Fibrosis

Deprived of their motor innervation during development, the affected extraocular muscles - most consistently the levator palpebrae superioris and superior rectus - are hypoplastic and atrophic, show increased internal nuclei and central mitochondrial clumping, and are progressively replaced by fibrous connective tissue. The muscles become mechanically restrictive, which is why forced duction testing is positive and why the ophthalmoplegia is restrictive rather than simply paralytic. Because the fibrosis is a consequence of denervation rather than a primary myopathy, no myopathic therapy addresses it.

extraocular skeletal muscle fiber CL:0008002 fibroblast CL:0000057

extraocular skeletal muscle development GO:0002074 ↓ DECREASED skeletal muscle atrophy GO:0014732 ↑ INCREASED collagen fibril organization in the fibrotic muscle GO:0030199 ↑ INCREASED

Downstream

Restrictive Non-Progressive Ophthalmoplegia with Ptosis Hypoplastic, fibrotic and mechanically tethered extraocular muscles fix the globe and prevent elevation, and a denervated levator produces ptosis.

Show evidence (2 references)

PMID:9066352 SUPPORT Human Clinical

"In addition, increased numbers of internal nuclei and central mitochondrial clumping are found in other extraocular muscles, suggesting that the muscle pathology extends beyond the muscles innervated by the superior division of cranial nerve III."

Documents the secondary myopathic changes and their extent beyond the denervated superior-division muscles.

PMID:9066352 REFUTE Human Clinical

"It has been generally thought that these clinical abnormalities result from myopathic fibrosis of the extraocular muscles."

Names the primary-myopathy model that the same study's neuropathology refutes, establishing the fibrosis as secondary.

Aberrant Reinnervation of Extraocular Muscles

Denervated extraocular muscles are secondarily and inappropriately reinnervated by misrouted branches of the surviving oculomotor nerve, most characteristically the lateral rectus. Because the aberrantly supplied muscle now fires with its new parent nerve rather than with its normal partner, the eye makes paradoxical, synkinetic movements - upshoots and downshoots on attempted adduction, A-pattern deviation, and in the rarest form synergistic divergence, in which attempted adduction produces abduction of both eyes. This is the same aberrant-reinnervation logic that produces globe retraction in Duane retraction syndrome.

aberrant motor neuron axon guidance to extraocular muscle GO:0008045 ↕ DYSREGULATED neuromuscular junction development at the misinnervated muscle GO:0007528 ↕ DYSREGULATED

Downstream

Restrictive Non-Progressive Ophthalmoplegia with Ptosis Synkinetic co-firing of aberrantly innervated muscles adds the aberrant residual eye movements that accompany the restriction.

Show evidence (2 references)

PMID:15671279 SUPPORT Human Clinical

"Orbital imaging in CFEOM1 due to various amino acid substitutions in the kinesin KIF21A demonstrates consistent abnormalities of motor and sensory innervation in the orbit."

Establishes consistent aberrant orbital innervation in genotyped CFEOM1.

PMID:34081534 SUPPORT Human Clinical

"Additionally, when one nerve is absent, its normal target muscles attract other motor neurons."

States the mechanism by which denervated extraocular muscles recruit aberrant innervation from a surviving nerve.

Commissural and Corticospinal Axon Guidance Failure

In the TUBB3 and TUBB2B subtypes the tubulin lesion is not confined to the ocular motor nerves. Long-range projection axons are also misrouted, producing dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts, and, for the TUBB2B E421K allele, polymicrogyria alongside the CFEOM. This arm is what converts an isolated eye movement disorder into a syndromic tubulinopathy, and it is the reason CFEOM3 carries the extraocular features that CFEOM1 does not.

callosal projection neuron CL:0000540

axon guidance of commissural and corticospinal projections GO:0007411 ↕ DYSREGULATED

Show evidence (2 references)

PMID:20074521 SUPPORT Human Clinical

"Neuroimaging reveals a spectrum of abnormalities including hypoplasia of oculomotor nerves and dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts."

Documents the commissural and corticospinal dysgenesis that accompanies the ocular lesion in TUBB3 disease.

PMID:23001566 SUPPORT Human Clinical

"Diffusion tensor imaging of brains of affected family members reveals aberrations in the trajectories of commissural projection neurons, implying a paucity of homotopic connections."

Human diffusion imaging shows the commissural misrouting in the TUBB2B CFEOM family.

Restrictive Non-Progressive Ophthalmoplegia with Ptosis

The clinical endpoint of the cascade. The eyes are held in a fixed, usually infraducted position and cannot be raised above the horizontal midline, ocular ductions are severely restricted in all directions, and there is bilateral blepharoptosis with poor levator function. The deficit is present from birth and does not progress, which distinguishes it from the acquired and progressive external ophthalmoplegias. Because both eyes are effectively immobile, patients adopt a compensatory chin-up head posture to see through the small residual field of gaze, and are at risk of amblyopia and exposure keratopathy.

Show evidence (2 references)

PMID:31313749 SUPPORT Human Clinical

"Congenital fibrosis of the extraocular muscles (CFEOM) is caused by abnormal development of the innervation of extraocular muscles."

A contemporary review states the neurogenic causal direction that this chain encodes.

PMID:16365788 SUPPORT Human Clinical

"Clinically, each patient had congenital bilateral ptosis, an infraducted primary position of each eye, and the inability to raise either eye above midline."

Describes the stereotyped clinical endpoint in genotyped patients.

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Pathograph

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Phenotypes

19

Eye 3

Bilateral Congenital Ptosis HP:0000508

Show evidence (1 reference)

PMID:15671279 SUPPORT Human Clinical

"Subjects with CFEOM1 had severe bilateral blepharoptosis, limited supraduction, and variable ophthalmoplegia."

Documents severe bilateral ptosis in a genotyped CFEOM1 cohort.

Restrictive External Ophthalmoplegia HP:0000544

Course: STABLE

Show evidence (2 references)

PMID:16365788 SUPPORT Human Clinical

"Clinically, each patient had congenital bilateral ptosis, an infraducted primary position of each eye, and the inability to raise either eye above midline."

Documents the restricted ductions and fixed infraducted position in genotyped CFEOM1 patients.

PMID:14597037 SUPPORT Human Clinical

"The two affected siblings had bilateral ptosis and exotropia and severe limitation of all extraocular movements."

Confirms the same severe restriction of all ductions in the recessive CFEOM2 subtype.

Strabismus HP:0000486

Show evidence (1 reference)

PMID:9066352 SUPPORT Human Clinical

"restrictive external ophthalmoplegia with the eyes partially or completely fixed in an infraducted (downward) and strabismic position"

Documents the fixed strabismic position of the eyes.

Head and Neck 1

Facial Palsy HP:0010628

Show evidence (1 reference)

PMID:20074521 SUPPORT Human Clinical

"Each mutation causes the ocular motility disorder CFEOM3, whereas some also result in intellectual and behavioral impairments, facial paralysis, and/or later-onset axonal sensorimotor polyneuropathy."

Lists facial paralysis among the allele-dependent extraocular features of TUBB3 disease.

Limbs 1

Syndactyly HP:0001159

Show evidence (1 reference)

PMID:15863670 SUPPORT Human Clinical

"The postaxial oligodactyly/oligosyndactyly of the hands was more severe on the right side."

Records the oligosyndactyly component of the Tukel hand anomaly.

Nervous System 3

Abnormal Corpus Callosum Morphology HP:0001273

Show evidence (1 reference)

PMID:20074521 SUPPORT Human Clinical

"Neuroimaging reveals a spectrum of abnormalities including hypoplasia of oculomotor nerves and dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts."

Reports corpus callosum dysgenesis on neuroimaging in TUBB3 disease.

Polymicrogyria HP:0002126

Show evidence (1 reference)

PMID:23001566 SUPPORT Human Clinical

"We have identified a novel inherited heterozygous missense mutation in TUBB2B that results in an E421K amino acid substitution in a family who segregates congenital fibrosis of the extraocular muscles (CFEOM) with polymicrogyria."

Documents co-segregation of polymicrogyria with CFEOM in the TUBB2B family.

Intellectual Disability HP:0001249

Show evidence (1 reference)

PMID:20074521 SUPPORT Human Clinical

"Each mutation causes the ocular motility disorder CFEOM3, whereas some also result in intellectual and behavioral impairments, facial paralysis, and/or later-onset axonal sensorimotor polyneuropathy."

Reports intellectual and behavioural impairment as an allele-dependent feature of TUBB3 disease.

Other 11

Congenital Fibrosis of the Extraocular Muscles Congenital fibrosis of extraocular muscles HP:0001491

Temporal: CHRONIC

Show evidence (1 reference)

PMID:9066352 SUPPORT Human Clinical

"Congenital fibrosis of the extraocular muscles is an autosomal dominant congenital disorder characterized by bilateral ptosis, restrictive external ophthalmoplegia with the eyes partially or completely fixed in an infraducted (downward) and strabismic position, and markedly limited and aberrant..."

States the defining clinical syndrome of congenital restrictive ophthalmoplegia with ptosis.

Exotropia HP:0000577

Show evidence (1 reference)

PMID:14597037 SUPPORT Human Clinical

"The two affected siblings had bilateral ptosis and exotropia and severe limitation of all extraocular movements."

Documents exotropia in molecularly confirmed CFEOM2 siblings.

Third Cranial Nerve Hypoplasia HP:6000597

Show evidence (2 references)

PMID:15671279 SUPPORT Human Clinical

"The oculomotor nerve was most severely hypoplastic, but the abducens was also affected."

Directly reports oculomotor nerve hypoplasia on orbital MRI in genotyped CFEOM1.

PMID:20074521 SUPPORT Human Clinical

"Neuroimaging reveals a spectrum of abnormalities including hypoplasia of oculomotor nerves and dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts."

Confirms oculomotor nerve hypoplasia in the TUBB3 (CFEOM3) subtype.

Sixth Cranial Nerve Hypoplasia HP:6000596

Show evidence (1 reference)

PMID:15671279 SUPPORT Human Clinical

"The oculomotor nerve was most severely hypoplastic, but the abducens was also affected."

Reports abducens involvement alongside the oculomotor nerve in genotyped CFEOM1.

Compensatory Chin-Up Head Posture Compensatory head posture HP:0031705

Show evidence (1 reference)

PMID:31848785 SUPPORT Human Clinical

"All the cases showed bilateral ptosis and a chin-up abnormal head posture (AHP)."

Documents the chin-up compensatory head posture in a paediatric CFEOM surgical series.

Refractive Error Abnormality of refraction HP:0000539

Show evidence (1 reference)

PMID:7724178 SUPPORT Human Clinical

"Refractive error and amblyopia also were variable"

Documents refractive error in the reported CFEOM cohort. No frequency band is asserted: "variable" describes spread, not a proportion, and per the frequency SOP that does not support a FrequencyEnum value.

Amblyopia HP:0000646

Show evidence (1 reference)

PMID:7724178 SUPPORT Human Clinical

"Refractive error and amblyopia also were variable."

Reports amblyopia, of variable degree, in a dominantly inherited congenital ocular fibrosis pedigree.

Corneal Scarring from Exposure Keratopathy HP:0000559

Show evidence (1 reference)

PMID:7724178 SUPPORT Human Clinical

"All affected members showed superficial keratopathy, many with corneal scarring."

Documents superficial keratopathy in all affected members and corneal scarring in many.

Optic Nerve Hypoplasia HP:0000609

Show evidence (1 reference)

PMID:15671279 SUPPORT Human Clinical

"Subjects with CFEOM1 exhibited subclinical but highly significant reduction from normal in mean optic nerve size (P < 0.001)."

Quantifies the reduction in optic nerve size that this phenotype records.

Peripheral Axonal Neuropathy HP:0003477

Show evidence (1 reference)

PMID:20074521 SUPPORT Human Clinical

"Each mutation causes the ocular motility disorder CFEOM3, whereas some also result in intellectual and behavioral impairments, facial paralysis, and/or later-onset axonal sensorimotor polyneuropathy."

Documents the later-onset axonal sensorimotor polyneuropathy of some TUBB3 alleles.

Postaxial Oligodactyly HP:0006210

Show evidence (1 reference)

PMID:15863670 SUPPORT Human Clinical

"The postaxial oligodactyly/oligosyndactyly of the hands was more severe on the right side."

Documents postaxial oligodactyly of the hands in the Tukel syndrome pedigree.

🧬

Genetic Associations

5

KIF21A (Causative)

Gene: KIF21A (anterograde kinesin motor) hgnc:19349 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (2 references)

PMID:14595441 SUPPORT Human Clinical

"We show that individuals with CFEOM1 harbor heterozygous missense mutations in a kinesin motor protein encoded by KIF21A. We identified six different mutations in 44 of 45 probands."

Establishes KIF21A as the CFEOM1 gene in 44 of 45 probands.

PMID:16365788 SUPPORT Human Clinical

"All affected members had a heterozygous mutation of the KIF21A gene in exon 21 (R954W)."

Documents the recurrent exon 21 p.R954W allele shared across unrelated families.

Variants (1)

KIF21A c.2860C>T (p.Arg954Trp)

Gene: KIF21A hgnc:19349 missense variant

The recurrent CFEOM1 allele, in exon 21 of the third coiled-coil stalk domain, found heterozygously across unrelated families of many ancestries. It acts by attenuating KIF21A autoinhibition, a gain of function, rather than by reducing protein activity.

Show evidence (1 reference)

PMID:16365788 SUPPORT Human Clinical

"All affected members had a heterozygous mutation of the KIF21A gene in exon 21 (R954W)."

Documents the recurrent heterozygous exon 21 p.R954W allele.

PHOX2A (Causative)

Gene: PHOX2A (ARIX; nIII/nIV homeodomain transcription factor) hgnc:691 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (2 references)

PMID:11600883 SUPPORT Human Clinical

"Two of the mutations are predicted to disrupt splicing, whereas the third alters an amino acid within the conserved brachyury-like domain."

Characterises the loss-of-function nature of the CFEOM2 PHOX2A alleles.

PMID:14597037 SUPPORT Human Clinical

"It confirms PHOX2A as the autosomal recessive CFEOM2 disease gene and provides evidence that the phenotypic differences between PHOX2A mutations in man and mouse do not result from hypomorphic PHOX2A alleles in humans."

Confirms PHOX2A as the recessive CFEOM2 gene through a nonsense allele.

Variants (1)

PHOX2A c.439C>T (p.Gln90Ter)

Gene: PHOX2A hgnc:691 nonsense variant

Homozygous nonsense allele truncating PHOX2A at the start of the homeodomain, reported in an Iranian CFEOM2 family. It joins the splice-disrupting and brachyury-like-domain missense alleles of the original CFEOM2 pedigrees as a loss-of-function change.

Show evidence (1 reference)

PMID:14597037 SUPPORT Human Clinical

"The 439C-->T mutation in this family changes a glutamine to a stop codon (Q90X) at the beginning of the PHOX2A homeodomain region."

Specifies the nonsense allele and its position at the homeodomain.

TUBB3 (Causative)

Gene: TUBB3 (neuron-specific beta-tubulin isotype III) hgnc:20772 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:20074521 SUPPORT Human Clinical

"We report that eight heterozygous missense mutations in TUBB3, encoding the neuron-specific beta-tubulin isotype III, result in a spectrum of human nervous system disorders that we now call the TUBB3 syndromes."

Establishes heterozygous TUBB3 missense variants as the cause of CFEOM3 and the wider TUBB3 syndromes.

TUBB2B (Causative)

Gene: TUBB2B (neuronal beta-tubulin isotype IIb) hgnc:30829 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:23001566 SUPPORT Human Clinical

"We have identified a novel inherited heterozygous missense mutation in TUBB2B that results in an E421K amino acid substitution in a family who segregates congenital fibrosis of the extraocular muscles (CFEOM) with polymicrogyria."

Identifies the single TUBB2B allele that causes CFEOM rather than isolated polymicrogyria.

Variants (1)

TUBB2B p.Glu421Lys

Gene: TUBB2B hgnc:30829 missense variant

An inherited heterozygous substitution altering a kinesin-binding site. It behaves differently from the other TUBB2B alleles, which cause polymicrogyria without primary axon dysinnervation.

Show evidence (1 reference)

PMID:23001566 SUPPORT In Vitro

"Interestingly, by incorporating into microtubules and altering their dynamic properties, the E421K substitution behaves differently than previously identified TUBB2B substitutions, providing mechanistic insight into the divergence between resulting phenotypes."

Distinguishes the CFEOM-causing E421K allele from other TUBB2B substitutions.

COL25A1 (Causative)

Gene: COL25A1 (CLAC-P neuronal transmembrane collagen) hgnc:18603 relationship_type: CAUSATIVE variant_origin: GERMLINE

Show evidence (1 reference)

PMID:25500261 SUPPORT Human Clinical

"By using linkage analysis, candidate gene screening, and exome sequencing, we identified three mutations in collagen, type XXV, alpha 1 (COL25A1) in individuals with autosomal-recessive inheritance of CCDD ophthalmic phenotypes."

Establishes biallelic COL25A1 variants as a cause of recessive CCDD with a CFEOM phenotype.

💊

Medical Actions

4

Inferior Rectus Recession (Strabismus Surgery)

Action: strabismus surgery Ontology label: Ophthalmologic Surgical Procedure NCIT:C15331

Bilateral recession of the tight, fibrotic inferior recti to raise the eyes towards the horizontal midline and relieve the compensatory chin-up head posture. Surgery rebalances the globes mechanically; it does not restore innervation or ocular motility. A secondary exotropia, often A-pattern, emerges after inferior rectus recession because adduction is further weakened, so horizontal surgery is deliberately staged until the vertical result has declared itself.

Mechanism Target:

MODULATES Denervation-Driven Extraocular Muscle Maldevelopment and Fibrosis — Recession lengthens the restrictive fibrotic muscle and so relieves the mechanical tether, without addressing the upstream dysinnervation.

Show evidence (1 reference)

PMID:31848785 SUPPORT Human Clinical

"Bilateral IR recession in pediatric patients with CFEOM was effective in improving AHP, but postoperative exotropia appeared to be inevitable owing to the diminished adducted function caused by IR recession."

Documents both the benefit on head posture and the mechanical trade-off of recessing the fibrotic muscle.

Show evidence (2 references)

PMID:31848785 SUPPORT Human Clinical

"Thus, horizontal strabismus surgery should be planned after the results of IR recession become evident."

Supports the staged surgical strategy recorded in this treatment entry.

PMID:31313749 SUPPORT Human Clinical

"Surgical management of patients with CFEOM continues to be challenging."

A contemporary review qualifies the expected benefit of strabismus surgery in CFEOM.

Frontalis Suspension for Ptosis

Action: frontalis suspension ptosis surgery Ontology label: Ophthalmologic Surgical Procedure NCIT:C15331

Suspension of the eyelid to the frontalis muscle, typically with a silicone sling, to lift the ptotic lid when levator function is too poor for levator surgery. Lid elevation must be judged against the risk of exposure keratopathy, since the immobile, infraducted globe and absent Bell phenomenon leave the cornea vulnerable once the lid is raised.

Mechanism Target:

BYPASSES Bilateral Congenital Ptosis — The sling substitutes frontalis action for the denervated levator palpebrae superioris, mechanically bypassing rather than correcting the dysinnervation.

Show evidence (1 reference)

PMID:37364855 SUPPORT Human Clinical

"Complex cases included blepharophimosis epicanthus inversus syndrome (n = 35), Marcus Gunn jaw-winking syndrome (n = 12), oculomotor palsy (n = 8), congenital fibrosis of extraocular muscles (n = 3), chronic progressive external ophthalmoplegia (n = 3), and others."

Places CFEOM among the complex ptosis indications treated by silicone sling frontalis suspension in this cohort.

Show evidence (1 reference)

PMID:37364855 SUPPORT Human Clinical

"Silicone sling FS has a favourable outcome in 70% of pediatric patients."

Quantifies the expected outcome of the procedure in the paediatric population that includes CFEOM.

Amblyopia and Refractive Management

Action: refractive correction and amblyopia therapy Ontology label: Supportive Care NCIT:C15747

Spectacle correction of refractive error together with occlusion or penalization of the better-seeing eye. Because the motility deficit is static and surgically irreversible, protecting visual development is the part of management with the greatest effect on final acuity.

Mechanism Target:

MODULATES Amblyopia — Correcting refractive error and forcing use of the amblyopic eye addresses the deprivational and refractive contributions to visual loss, which are independent of the dysinnervation itself.

Show evidence (1 reference)

PMID:7724178 SUPPORT Human Clinical

"Refractive error and amblyopia also were variable."

Establishes refractive error and amblyopia as variable, and therefore individually assessable and treatable, features.

Genetic Counseling

Action: genetic counseling Ontology label: Genetic Counseling NCIT:C15240

Molecular testing distinguishes the autosomal dominant KIF21A, TUBB3, and TUBB2B subtypes from the autosomal recessive PHOX2A and COL25A1 subtypes, which carry very different recurrence risks, and identifies the TUBB3 and TUBB2B genotypes that warrant surveillance for the extraocular neurological features.

Show evidence (1 reference)

PMID:20074521 SUPPORT Human Clinical

"Each mutation causes the ocular motility disorder CFEOM3, whereas some also result in intellectual and behavioral impairments, facial paralysis, and/or later-onset axonal sensorimotor polyneuropathy."

Allele-dependent extraocular features are the reason genotype changes counselling and surveillance in CFEOM.

🔬

Diagnosis

3

High-resolution orbital MRI

Thin-section orbital MRI demonstrates hypoplasia of the affected extraocular muscles together with hypoplasia and misdirection of the motor nerves that supply them. This is the modality that established the neurogenic basis of CFEOM, and so is the imaging counterpart of the causal direction this entry models: the nerve lesion is visible alongside the muscle lesion it causes.

magnetic resonance imaging NCIT:C16809

Show evidence (1 reference)

PMID:34081534 SUPPORT Human Clinical

"MRI of fourteen individuals with CFEOM1 and KIF21A mutations from six families demonstrated profound hypoplasia of the SR and LPS muscles, and hypoplasia and misdirection of all the motor nerves in the orbit"

Establishes orbital MRI as the investigation that shows both the muscle hypoplasia and the nerve hypoplasia and misdirection underlying it.

Brain MRI for associated central malformations

Brain imaging identifies the central nervous system malformations that accompany the tubulinopathy forms, and so contributes to distinguishing CFEOM3 from the more restricted CFEOM1 phenotype.

magnetic resonance imaging NCIT:C16809

Show evidence (1 reference)

PMID:20074521 SUPPORT Human Clinical

"Neuroimaging reveals a spectrum of abnormalities including hypoplasia of oculomotor nerves and dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts"

Names the central malformations neuroimaging detects in the TUBB3 forms, which is what makes brain imaging diagnostically informative here.

Exome or genome sequencing

Molecular diagnosis rests on sequencing the known CFEOM genes; broader exome or genome sequencing is used for the substantial fraction of ocular congenital cranial dysinnervation disorders that remain genetically unsolved after targeted testing.

genetic testing NCIT:C15709

Show evidence (1 reference)

PMID:39033378 SUPPORT Human Clinical

"We coupled phenotyping with exome or genome sequencing of 467 probands"

Documents exome or genome sequencing as the strategy applied to genetically unsolved ocular CCDD probands, the group CFEOM sits within.

{ }

Source YAML

click to show

name: Congenital Fibrosis of the Extraocular Muscles
creation_date: "2026-08-20T00:00:00Z"
category: Mendelian
disease_term:
  preferred_term: congenital fibrosis of extraocular muscles
  term:
    id: MONDO:0007614
    label: congenital fibrosis of extraocular muscles
description: >-
  Congenital fibrosis of the extraocular muscles (CFEOM) is a congenital,
  non-progressive restrictive ophthalmoplegia with blepharoptosis, in which the
  eyes are held in a fixed, usually infraducted position and cannot be elevated
  above the horizontal midline. Despite the name, CFEOM is not a primary
  myopathy: it is a congenital cranial dysinnervation disorder (CCDD). The
  primary lesion lies in the developing oculomotor (cranial nerve III) and
  trochlear (cranial nerve IV) nuclei and their axons; neuropathology and
  high-resolution orbital MRI show absent or hypoplastic ocular motor nerves and
  loss of the corresponding alpha motor neurons, with the extraocular muscle
  atrophy and "fibrosis" that gives the disorder its name arising secondarily
  from denervation. Aberrant reinnervation of denervated muscles by misrouted
  branches of the surviving oculomotor nerve produces the synkinetic and
  paradoxical residual eye movements that are characteristic of the disorder.
  Four principal molecular routes converge on this lesion: gain-of-function
  missense variants in the anterograde kinesin KIF21A that attenuate its
  autoinhibition and stall superior-division oculomotor axons (CFEOM1, and the
  dominant CFEOM3B); recessive loss of the homeodomain transcription factor
  PHOX2A/ARIX, which is required to specify the nIII/nIV motor nuclei (CFEOM2);
  heterozygous missense variants in the neuron-specific beta-tubulins TUBB3 and
  TUBB2B that alter microtubule dynamics and microtubule-kinesin interaction
  (CFEOM3, with variable CNS involvement); and recessive loss of COL25A1
  (CFEOM5). CFEOM sits in the CCDD family alongside Duane retraction syndrome,
  Moebius syndrome, and horizontal gaze palsy with progressive scoliosis, all of
  which arise from maldevelopment or miswiring of ocular motor cranial nerves
  rather than from a primary muscle defect. Management is supportive and
  surgical - inferior rectus recession to correct the chin-up head posture,
  ptosis suspension surgery, refractive correction, and amblyopia therapy - and
  does not restore normal ocular motility.
parents:
- ocular motility disease
- congenital nervous system disorder
- hereditary neurological disease
- disorder of development or morphogenesis
inheritance:
- name: Autosomal dominant inheritance
  description: >-
    CFEOM1 and CFEOM3 (KIF21A, TUBB3, TUBB2B) are inherited in an autosomal
    dominant manner; affected individuals are heterozygous for a missense
    variant.
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  evidence:
  - reference: PMID:14595441
    reference_title: "Heterozygous mutations of the kinesin KIF21A in congenital fibrosis of the extraocular muscles type 1 (CFEOM1)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Congenital fibrosis of the extraocular muscles type 1 (CFEOM1; OMIM
      #135700) is an autosomal dominant strabismus disorder associated with
      defects of the oculomotor nerve.
    explanation: >-
      Establishes CFEOM1, the commonest form, as an autosomal dominant disorder
      of the oculomotor nerve.
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report that eight heterozygous missense mutations in TUBB3, encoding
      the neuron-specific beta-tubulin isotype III, result in a spectrum of
      human nervous system disorders that we now call the TUBB3 syndromes.
    explanation: >-
      Heterozygous TUBB3 missense variants are sufficient to cause CFEOM3,
      supporting autosomal dominant transmission of that subtype.
- name: Autosomal recessive inheritance
  description: >-
    CFEOM2 (PHOX2A/ARIX), CFEOM5 (COL25A1), and the Tukel syndrome variant are
    inherited in an autosomal recessive manner, and have been described mainly in
    consanguineous families.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:14597037
    reference_title: "A novel PHOX2A/ARIX mutation in an Iranian family with congenital fibrosis of extraocular muscles type 2 (CFEOM2)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Both parents and the unaffected siblings were heterozygous,and the two
      affected siblings were homozygous for this mutation.
    explanation: >-
      Homozygous affected siblings with heterozygous unaffected parents
      establishes autosomal recessive transmission of CFEOM2.
  - reference: PMID:25500261
    reference_title: "Recessive mutations in COL25A1 are a cause of congenital cranial dysinnervation disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we identified three mutations in collagen, type XXV, alpha 1 (COL25A1) in
      individuals with autosomal-recessive inheritance of CCDD ophthalmic
      phenotypes.
    explanation: >-
      Establishes autosomal recessive inheritance for the COL25A1 (CFEOM5) form.
references:
- reference: PMID:20301522
  title: "Congenital Fibrosis of the Extraocular Muscles Overview."
  tags:
  - GeneReviews
- reference: PMID:9066352
  title: "Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles."
- reference: PMID:15671279
  title: "Magnetic resonance imaging evidence for widespread orbital dysinnervation in congenital fibrosis of extraocular muscles due to mutations in KIF21A."
- reference: PMID:14595441
  title: "Heterozygous mutations of the kinesin KIF21A in congenital fibrosis of the extraocular muscles type 1 (CFEOM1)."
- reference: PMID:24656932
  title: "Human CFEOM1 mutations attenuate KIF21A autoinhibition and cause oculomotor axon stalling."
- reference: PMID:11600883
  title: "Homozygous mutations in ARIX(PHOX2A) result in congenital fibrosis of the extraocular muscles type 2."
- reference: PMID:20074521
  title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
- reference: PMID:23001566
  title: "An inherited TUBB2B mutation alters a kinesin-binding site and causes polymicrogyria, CFEOM and axon dysinnervation."
- reference: PMID:25500261
  title: "Recessive mutations in COL25A1 are a cause of congenital cranial dysinnervation disorder."
- reference: PMID:15863670
  title: "A new syndrome, congenital extraocular muscle fibrosis with ulnar hand anomalies, maps to chromosome 21qter."
- reference: PMID:31313749
  title: "Congenital fibrosis of the extraocular muscles: review of recent literature."
- reference: PMID:31848785
  title: "Surgical management of pediatric patients with congenital fibrosis of the extraocular muscles."
- reference: PMID:34081534
  title: "Axonal Growth Abnormalities Underlying Ocular Cranial Nerve Disorders."
- reference: PMID:39033378
  title: "Expanding the genetics and phenotypes of ocular congenital cranial dysinnervation disorders."
has_subtypes:
- name: CFEOM1
  display_name: CFEOM1 (KIF21A, classic bilateral CFEOM)
  classification: genetic
  subtype_term:
    preferred_term: congenital fibrosis of extraocular muscles type 1
    term:
      id: MONDO:0021083
      label: congenital fibrosis of extraocular muscles type 1
  genes:
  - preferred_term: KIF21A
    term:
      id: hgnc:19349
      label: KIF21A
  description: >-
    The classic and most common form. Autosomal dominant, fully penetrant, and
    bilateral: both eyes are fixed in a downward (infraducted) position with
    severe bilateral ptosis and inability to elevate either eye above the
    horizontal midline. Caused by heterozygous missense variants in the kinesin
    KIF21A, with recurrent hotspots in the third coiled-coil stalk domain
    (p.R954W is by far the commonest allele, recurring across ancestries).
  evidence:
  - reference: PMID:14595441
    reference_title: "Heterozygous mutations of the kinesin KIF21A in congenital fibrosis of the extraocular muscles type 1 (CFEOM1)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We show that individuals with CFEOM1 harbor heterozygous missense
      mutations in a kinesin motor protein encoded by KIF21A. We identified six
      different mutations in 44 of 45 probands.
    explanation: >-
      Establishes heterozygous KIF21A missense variants as the cause of CFEOM1
      in nearly all probands tested.
  - reference: PMID:16365788
    reference_title: "Recurrent mutation of the KIF21A gene in Japanese patients with congenital fibrosis of the extraocular muscles."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Clinically, each patient had congenital bilateral ptosis, an infraducted
      primary position of each eye, and the inability to raise either eye above
      midline.
    explanation: >-
      Defines the stereotyped bilateral CFEOM1 clinical picture in KIF21A
      p.R954W carriers.
- name: CFEOM2
  display_name: CFEOM2 (PHOX2A/ARIX, autosomal recessive)
  classification: genetic
  subtype_term:
    preferred_term: fibrosis of extraocular muscles, congenital, 2
    term:
      id: MONDO:0011181
      label: fibrosis of extraocular muscles, congenital, 2
  genes:
  - preferred_term: PHOX2A
    term:
      id: hgnc:691
      label: PHOX2A
  description: >-
    Autosomal recessive form, described mainly in consanguineous Middle Eastern
    families. Affected individuals have bilateral ptosis with the eyes fixed in
    an exotropic (outward) rather than infraducted position and severe
    limitation of all extraocular movements. Caused by biallelic loss of
    PHOX2A/ARIX, a homeodomain transcription factor required for specification of
    the oculomotor and trochlear motor nuclei.
  evidence:
  - reference: PMID:11600883
    reference_title: "Homozygous mutations in ARIX(PHOX2A) result in congenital fibrosis of the extraocular muscles type 2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we report three mutations in ARIX (also known as PHOX2A) in four
      CFEOM2 pedigrees.
    explanation: >-
      Identifies PHOX2A/ARIX as the CFEOM2 disease gene across four pedigrees.
  - reference: PMID:14597037
    reference_title: "A novel PHOX2A/ARIX mutation in an Iranian family with congenital fibrosis of extraocular muscles type 2 (CFEOM2)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The two affected siblings had bilateral ptosis and exotropia and severe
      limitation of all extraocular movements.
    explanation: >-
      Documents the distinguishing exotropic primary position of CFEOM2.
- name: CFEOM3A
  display_name: CFEOM3A (TUBB3, with or without extraocular involvement)
  classification: genetic
  subtype_term:
    preferred_term: fibrosis of extraocular muscles, congenital, 3A, with or without extraocular involvement
    term:
      id: MONDO:0010912
      label: fibrosis of extraocular muscles, congenital, 3A, with or without extraocular involvement
  genes:
  - preferred_term: TUBB3
    term:
      id: hgnc:20772
      label: TUBB3
  description: >-
    Autosomal dominant, more variable and often asymmetric or unilateral form
    caused by heterozygous missense variants in TUBB3, the neuron-specific
    beta-tubulin isotype III. Unlike CFEOM1, the eyes are not always infraducted
    and one eye may be spared. Some TUBB3 alleles add extraocular features -
    intellectual and behavioural impairment, facial weakness, and a later-onset
    axonal sensorimotor polyneuropathy - together with commissural and
    corticospinal tract dysgenesis on neuroimaging. See the separate
    TUBB3-related Tubulinopathy entry for the wider TUBB3 syndrome spectrum.
  evidence:
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Each mutation causes the ocular motility disorder CFEOM3, whereas some
      also result in intellectual and behavioral impairments, facial paralysis,
      and/or later-onset axonal sensorimotor polyneuropathy.
    explanation: >-
      Defines CFEOM3 as the constant ocular phenotype of TUBB3 missense variants
      with variable additional neurological features.
- name: CFEOM3B
  display_name: CFEOM3B (KIF21A)
  classification: genetic
  subtype_term:
    preferred_term: fibrosis of extraocular muscles, congenital, 3b
    term:
      id: MONDO:0800209
      label: fibrosis of extraocular muscles, congenital, 3b
  genes:
  - preferred_term: KIF21A
    term:
      id: hgnc:19349
      label: KIF21A
  description: >-
    A CFEOM3-pattern (variable, potentially unilateral or asymmetric, eyes not
    obligately infraducted) phenotype caused by KIF21A variants rather than
    TUBB3, showing that the same KIF21A allele can produce either the classic
    CFEOM1 pattern or a CFEOM3 pattern within and between families.
  evidence:
  - reference: PMID:27513105
    reference_title: "KIF21A mutation in two Chinese families with congenital fibrosis of the extraocular muscles type 1 and 3."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The results indicated that, in the patients with CFEOM1 and CFEOM3, the
      disease was caused by the same KIF21A gene mutation.
    explanation: >-
      Demonstrates that a single recurrent KIF21A allele underlies both the
      CFEOM1 and CFEOM3 clinical patterns.
- name: CFEOM3C
  display_name: CFEOM3C (13q12.11-linked)
  classification: genetic
  subtype_term:
    preferred_term: fibrosis of extraocular muscles, congenital, 3c
    term:
      id: MONDO:0012262
      label: fibrosis of extraocular muscles, congenital, 3c
  description: >-
    A locus-defined CFEOM3 subtype mapped by linkage in a family without a
    KIF21A or TUBB3 variant. It is retained here as a distinct nosological
    entity because the causal gene at the locus is not established, so the
    subtype cannot yet be folded into a gene-defined class.
- name: CFEOM5
  display_name: CFEOM5 (COL25A1, autosomal recessive)
  classification: genetic
  subtype_term:
    preferred_term: fibrosis of extraocular muscles, congenital, 5
    term:
      id: MONDO:0014538
      label: fibrosis of extraocular muscles, congenital, 5
  genes:
  - preferred_term: COL25A1
    term:
      id: hgnc:18603
      label: COL25A1
  description: >-
    Autosomal recessive CCDD with a CFEOM ophthalmic phenotype caused by
    biallelic COL25A1 variants that reduce protein stability or level. COL25A1
    encodes CLAC-P, a transmembrane collagen implicated in oculomotor neuron
    development, placing this subtype outside the cytoskeletal and
    transcription-factor mechanisms of the other subtypes.
  evidence:
  - reference: PMID:25500261
    reference_title: "Recessive mutations in COL25A1 are a cause of congenital cranial dysinnervation disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our data suggest that lack of COL25A1 might interfere with molecular
      pathways involved in oculomotor neuron development, leading to CCDD
      phenotypes.
    explanation: >-
      Assigns the COL25A1 subtype to the same oculomotor-neuron developmental
      mechanism as the rest of the CFEOM spectrum.
- name: Tukel syndrome
  display_name: Tukel syndrome (CFEOM with postaxial ulnar hand anomalies)
  classification: genetic
  subtype_term:
    preferred_term: Tukel syndrome
    term:
      id: MONDO:0012270
      label: Tukel syndrome
  description: >-
    An autosomal recessive syndromic variant in which non-progressive
    restrictive ophthalmoplegia with blepharoptosis is accompanied by postaxial
    (ulnar) oligodactyly or oligosyndactyly of the hands. Described in a large
    consanguineous Turkish family and mapped by linkage to chromosome 21qter;
    the causal gene remains unidentified. The co-occurrence of a cranial
    dysinnervation phenotype with a posterior limb-patterning defect is the
    feature that distinguishes it from isolated CFEOM.
  evidence:
  - reference: PMID:15863670
    reference_title: "A new syndrome, congenital extraocular muscle fibrosis with ulnar hand anomalies, maps to chromosome 21qter."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The postaxial oligodactyly/oligosyndactyly of the hands was more severe on
      the right side.
    explanation: >-
      Defines the ulnar hand anomaly that distinguishes Tukel syndrome from
      isolated CFEOM.
  - reference: PMID:15863670
    reference_title: "A new syndrome, congenital extraocular muscle fibrosis with ulnar hand anomalies, maps to chromosome 21qter."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A genome-wide scan established linkage of this new autosomal recessive
      syndrome to a locus on chromosome 21qter.
    explanation: >-
      Establishes the recessive inheritance and 21qter locus of Tukel syndrome.
pathophysiology:
- name: KIF21A Kinesin Autoinhibition Loss
  biological_scale: MOLECULAR
  description: >-
    KIF21A is an anterograde kinesin whose motor activity is normally restrained
    by an intramolecular autoinhibitory interaction between its third coiled-coil
    stalk and its motor domain. The recurrent CFEOM1 missense variants cluster in
    exactly these two elements and attenuate that autoinhibition, so the motor is
    inappropriately active. This is a gain-of-function lesion, not haploinsufficiency,
    which is why heterozygous missense variants are pathogenic while KIF21A null
    alleles are not a recognised cause of CFEOM.
  molecular_functions:
  - preferred_term: KIF21A microtubule motor activity
    term:
      id: GO:0003777
      label: microtubule motor activity
    modifier: GAIN_OF_FUNCTION
  cell_types:
  - preferred_term: oculomotor alpha motor neuron
    term:
      id: CL:0008038
      label: alpha motor neuron
  evidence:
  - reference: PMID:24656932
    reference_title: "Human CFEOM1 mutations attenuate KIF21A autoinhibition and cause oculomotor axon stalling."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      We establish a gain-of-function mechanism and find that human motor or
      stalk mutations attenuate Kif21a autoinhibition, providing in vivo
      evidence for mammalian kinesin autoregulation.
    explanation: >-
      Establishes attenuated KIF21A autoinhibition as the gain-of-function
      molecular lesion in CFEOM1.
  - reference: PMID:14595441
    reference_title: "Heterozygous mutations of the kinesin KIF21A in congenital fibrosis of the extraocular muscles type 1 (CFEOM1)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The primary mutational hotspots are in the stalk domain, highlighting an
      important new role for KIF21A and its stalk in the formation of the
      oculomotor axis.
    explanation: >-
      Localises the CFEOM1 variants to the stalk domain that mediates
      autoinhibition.
  downstream:
  - target: Oculomotor Axon Stalling and Aberrant Growth Cone Guidance
    causal_link_type: DIRECT
    description: >-
      A disinhibited KIF21A motor perturbs the axonal cytoskeleton of the
      developing oculomotor nerve, and its superior-division axons fail to
      advance normally.
    evidence:
    - reference: PMID:24656932
      reference_title: "Human CFEOM1 mutations attenuate KIF21A autoinhibition and cause oculomotor axon stalling."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        We demonstrate that Kif21a knockin mice harboring the most common human
        mutation develop CFEOM. The developing axons of the oculomotor nerve's
        superior division stall in the proximal nerve; the growth cones enlarge,
        extend excessive filopodia, and assume random trajectories.
      explanation: >-
        A knockin mouse carrying the common human allele shows the stalling and
        growth-cone disorganisation this edge asserts.
- name: PHOX2A-Dependent Oculomotor and Trochlear Nucleus Specification Failure
  biological_scale: CELLULAR
  description: >-
    PHOX2A (ARIX) is a homeodomain transcription factor required to specify the
    midbrain oculomotor (nIII) and trochlear (nIV) motor nuclei. Biallelic
    loss-of-function variants remove that determinant, so the motor neuron pools
    that should innervate the extraocular muscles are never properly formed. This
    is the CFEOM2 route into the shared downstream lesion, and it is upstream of
    axon guidance rather than a guidance defect itself.
  molecular_functions:
  - preferred_term: PHOX2A homeodomain transcription factor activity
    term:
      id: GO:0003700
      label: DNA-binding transcription factor activity
    modifier: LOSS_OF_FUNCTION
  biological_processes:
  - preferred_term: oculomotor nerve development
    term:
      id: GO:0021557
      label: oculomotor nerve development
    modifier: DECREASED
  - preferred_term: trochlear nerve development
    term:
      id: GO:0021558
      label: trochlear nerve development
    modifier: DECREASED
  cell_types:
  - preferred_term: oculomotor and trochlear alpha motor neuron
    term:
      id: CL:0008038
      label: alpha motor neuron
  evidence:
  - reference: PMID:11600883
    reference_title: "Homozygous mutations in ARIX(PHOX2A) result in congenital fibrosis of the extraocular muscles type 2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      ARIX encodes a homeodomain transcription factor protein previously shown
      to be required for nIII/nIV development in mouse and zebrafish.
    explanation: >-
      Identifies the developmental role of PHOX2A/ARIX in the oculomotor and
      trochlear nuclei that biallelic loss removes.
  - reference: PMID:11600883
    reference_title: "Homozygous mutations in ARIX(PHOX2A) result in congenital fibrosis of the extraocular muscles type 2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These findings confirm the hypothesis that CFEOM2 results from the
      abnormal development of nIII/nIV (ref. 7) and emphasize a critical role
      for ARIX in the development of these midbrain motor nuclei.
    explanation: >-
      Directly attributes CFEOM2 to abnormal development of the nIII/nIV motor
      nuclei.
  - reference: PMID:34081534
    reference_title: "Axonal Growth Abnormalities Underlying Ocular Cranial Nerve Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These disorders can arise through one of two mechanisms: (a) defective
      motor neuron specification, usually by loss of a transcription factor
      necessary for brainstem patterning, or (b) axon growth and guidance
      abnormalities of the oculomotor, trochlear, and abducens nerves.
    explanation: >-
      Places the PHOX2A lesion in the transcription-factor specification arm of
      the two recognised CCDD mechanisms.
  downstream:
  - target: Hypoplasia of the Oculomotor and Trochlear Nerves
    causal_link_type: DIRECT
    description: >-
      Motor nuclei that are never specified cannot send out a normal nerve, so
      the nIII and nIV trunks are absent or hypoplastic.
    evidence:
    - reference: PMID:11600883
      reference_title: "Homozygous mutations in ARIX(PHOX2A) result in congenital fibrosis of the extraocular muscles type 2."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Neuropathologic studies indicate that these disorders may result from
        the maldevelopment of the oculomotor (nIII), trochlear (nIV) and
        abducens (nVI) cranial nerve nuclei.
      explanation: >-
        Links nuclear maldevelopment to the cranial nerve lesion that defines
        the congenital fibrosis syndromes.
- name: Beta-Tubulin Microtubule Dysfunction in Cranial Motor Neurons
  biological_scale: MOLECULAR
  description: >-
    TUBB3 and TUBB2B encode neuron-enriched beta-tubulin isotypes that
    heterodimerise with alpha-tubulin to build the dynamic microtubules of the
    growing axon and its growth cone. The CFEOM3-causing missense variants
    impair heterodimer formation, alter microtubule dynamic instability, and in a
    subset also disrupt the interface through which kinesin motors engage the
    microtubule lattice. The convergence of this arm with the KIF21A arm on the
    same clinical phenotype - one lesion in the track, the other in the motor -
    is the strongest mechanistic argument that CFEOM is a disorder of axonal
    transport and guidance.
  molecular_functions:
  - preferred_term: beta-tubulin structural constituent of the neuronal microtubule
    term:
      id: GO:0005200
      label: structural constituent of cytoskeleton
    modifier: DYSREGULATED
  - preferred_term: microtubule-kinesin interaction
    term:
      id: GO:0019894
      label: kinesin binding
    modifier: DECREASED
  biological_processes:
  - preferred_term: tubulin heterodimer formation
    term:
      id: GO:0007021
      label: tubulin complex assembly
    modifier: DECREASED
  cell_types:
  - preferred_term: cranial motor neuron
    term:
      id: CL:0000100
      label: motor neuron
  evidence:
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Modeling each mutation in yeast tubulin demonstrates that all alter
      dynamic instability whereas a subset disrupts the interaction of
      microtubules with kinesin motors.
    explanation: >-
      Establishes altered microtubule dynamics in every allele and disrupted
      microtubule-kinesin interaction in a subset.
  - reference: PMID:23001566
    reference_title: "An inherited TUBB2B mutation alters a kinesin-binding site and causes polymicrogyria, CFEOM and axon dysinnervation."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      TUBB2B-E421K αβ-heterodimers are incorporated into the microtubule
      network where they alter microtubule dynamics and can reduce kinesin
      localization.
    explanation: >-
      Shows the CFEOM-causing TUBB2B allele acts through the same
      dynamics-and-kinesin mechanism as the TUBB3 alleles.
  downstream:
  - target: Oculomotor Axon Stalling and Aberrant Growth Cone Guidance
    causal_link_type: DIRECT
    description: >-
      Microtubules whose dynamics and kinesin engagement are perturbed cannot
      support normal growth-cone steering in the developing ocular motor nerves.
    evidence:
    - reference: PMID:20074521
      reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        A knock-in disease mouse model reveals axon guidance defects without
        evidence of cortical cell migration abnormalities.
      explanation: >-
        The knock-in model isolates axon guidance, not neuronal migration, as
        the consequence of the TUBB3 lesion.
  - target: Commissural and Corticospinal Axon Guidance Failure
    causal_link_type: DIRECT
    description: >-
      The same tubulin lesion also perturbs guidance of callosal and other
      long-range projection axons, which is why some TUBB3 and TUBB2B alleles
      add central nervous system features to the ocular phenotype.
    evidence:
    - reference: PMID:23001566
      reference_title: "An inherited TUBB2B mutation alters a kinesin-binding site and causes polymicrogyria, CFEOM and axon dysinnervation."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Expression of exogenous Tubb2b-E421K in developing callosal projection
        neurons is sufficient to perturb homotopic connectivity, without
        affecting neuronal production or migration.
      explanation: >-
        Shows the tubulin lesion is sufficient to disrupt callosal connectivity
        independently of migration.
- name: COL25A1 Loss in Oculomotor Neuron Development
  biological_scale: MOLECULAR
  description: >-
    COL25A1 encodes CLAC-P, a neuronal transmembrane collagen. Biallelic
    variants that reduce its stability or abundance perturb the molecular
    programme of oculomotor neuron development and alter the levels of
    axon-guidance-associated proteins including soluble APP and TUBB3 itself,
    connecting this recessive subtype back to the shared cytoskeletal arm.
  cell_types:
  - preferred_term: oculomotor neuron
    term:
      id: CL:0000100
      label: motor neuron
  biological_processes:
  - preferred_term: oculomotor nerve development
    term:
      id: GO:0021557
      label: oculomotor nerve development
    modifier: DECREASED
  evidence:
  - reference: PMID:25500261
    reference_title: "Recessive mutations in COL25A1 are a cause of congenital cranial dysinnervation disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We further detected altered levels of sAPP (neuronal protein involved in
      axon guidance and synaptogenesis) and TUBB3 (encoded by TUBB3, which is
      mutated in CFEOM3) as a result of null mutations in COL25A1.
    explanation: >-
      Connects COL25A1 loss to the axon-guidance machinery shared with the other
      CFEOM subtypes.
  downstream:
  - target: Hypoplasia of the Oculomotor and Trochlear Nerves
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - Disturbed oculomotor neuron development
    - Altered levels of axon-guidance-associated proteins including sAPP and TUBB3
    description: >-
      Loss of COL25A1 interferes with the developmental programme that builds
      the ocular motor nerves.
    evidence:
    - reference: PMID:25500261
      reference_title: "Recessive mutations in COL25A1 are a cause of congenital cranial dysinnervation disorder."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Our data suggest that lack of COL25A1 might interfere with molecular
        pathways involved in oculomotor neuron development, leading to CCDD
        phenotypes.
      explanation: >-
        States the inferred causal route from COL25A1 loss to a cranial
        dysinnervation phenotype.
- name: Oculomotor Axon Stalling and Aberrant Growth Cone Guidance
  biological_scale: CELLULAR
  description: >-
    The convergent cellular lesion of the cytoskeletal CFEOM subtypes. Axons of
    the oculomotor nerve, and most consistently those of its superior division
    that supply the levator palpebrae superioris and superior rectus, stall in
    the proximal nerve. Their growth cones enlarge, extend excessive filopodia,
    and take random trajectories instead of following their stereotyped path to
    the orbit; axons of the inferior division reach the orbit but branch
    ectopically. This selective vulnerability of the developing oculomotor nerve
    to perturbations of the axon cytoskeleton is what makes an otherwise
    ubiquitously expressed motor or tubulin lesion present as an isolated eye
    movement disorder.
  biological_processes:
  - preferred_term: motor neuron axon guidance
    term:
      id: GO:0008045
      label: motor neuron axon guidance
    modifier: DYSREGULATED
  - preferred_term: axon extension of the oculomotor nerve
    term:
      id: GO:0048675
      label: axon extension
    modifier: DECREASED
  cell_types:
  - preferred_term: oculomotor alpha motor neuron
    term:
      id: CL:0008038
      label: alpha motor neuron
  evidence:
  - reference: PMID:24656932
    reference_title: "Human CFEOM1 mutations attenuate KIF21A autoinhibition and cause oculomotor axon stalling."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Inferior division axons reach the orbit but branch ectopically.
    explanation: >-
      Documents the divergent fate of inferior-division axons alongside the
      stalled superior division.
  - reference: PMID:24656932
    reference_title: "Human CFEOM1 mutations attenuate KIF21A autoinhibition and cause oculomotor axon stalling."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      highlights a selective vulnerability of the developing oculomotor nerve to
      perturbations of the axon cytoskeleton
    explanation: >-
      States the selective vulnerability that explains the restricted phenotype.
  - reference: PMID:34081534
    reference_title: "Axonal Growth Abnormalities Underlying Ocular Cranial Nerve Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Abnormalities of axon growth and guidance are often limited to a single
      nerve or subdivision, even when the causative gene is ubiquitously
      expressed.
    explanation: >-
      Establishes that the guidance defect is restricted to one nerve or nerve
      subdivision despite ubiquitous expression of the causal gene.
  downstream:
  - target: Hypoplasia of the Oculomotor and Trochlear Nerves
    causal_link_type: DIRECT
    description: >-
      Axons that stall or never arrive leave a structurally thin or absent nerve
      trunk and, over time, loss of the corresponding motor neurons.
    evidence:
    - reference: PMID:20074521
      reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Neuroimaging reveals a spectrum of abnormalities including hypoplasia of
        oculomotor nerves and dysgenesis of the corpus callosum, anterior
        commissure, and corticospinal tracts.
      explanation: >-
        Human neuroimaging confirms oculomotor nerve hypoplasia as the
        structural consequence of the guidance defect.
  - target: Aberrant Reinnervation of Extraocular Muscles
    causal_link_type: DIRECT
    description: >-
      Misrouted and ectopically branching oculomotor axons reach muscles they do
      not normally supply, most characteristically the lateral rectus.
    evidence:
    - reference: PMID:15671279
      reference_title: "Magnetic resonance imaging evidence for widespread orbital dysinnervation in congenital fibrosis of extraocular muscles due to mutations in KIF21A."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Subjects with the R954W and R954Q substitutions frequently exhibited
        A-pattern strabismus, with misinnervation of the lateral rectus muscle
        by an oculomotor nerve branch.
      explanation: >-
        Orbital MRI directly demonstrates oculomotor misinnervation of the
        lateral rectus in CFEOM1.
- name: Hypoplasia of the Oculomotor and Trochlear Nerves
  biological_scale: TISSUE
  description: >-
    The defining structural lesion of CFEOM and the point at which every
    molecular route converges. Autopsy of a chromosome-12-linked (CFEOM1) family
    showed absence of the superior division of the oculomotor nerve together with
    its alpha motor neurons; high-resolution orbital MRI in genotyped KIF21A
    carriers shows small or absent orbital motor nerves, with the oculomotor
    nerve most severely hypoplastic and the abducens also affected. The lesion is
    therefore not confined to nIII, and its extent is wider than the classic
    superior-division description implies.
  biological_processes:
  - preferred_term: oculomotor nerve morphogenesis
    term:
      id: GO:0021622
      label: oculomotor nerve morphogenesis
    modifier: DECREASED
  - preferred_term: cranial nerve development
    term:
      id: GO:0021545
      label: cranial nerve development
    modifier: DECREASED
  cell_types:
  - preferred_term: oculomotor alpha motor neuron
    term:
      id: CL:0008038
      label: alpha motor neuron
  evidence:
  - reference: PMID:9066352
    reference_title: "Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      There is an absence of the superior division of the oculomotor nerve and
      its corresponding alpha motor neurons, and abnormalities of the levator
      palpebrae superioris and rectus superior (the muscles innervated by the
      superior division of the oculomotor nerve).
    explanation: >-
      Human neuropathology establishes the missing nerve division and motor
      neuron pool as the primary lesion.
  - reference: PMID:15671279
    reference_title: "Magnetic resonance imaging evidence for widespread orbital dysinnervation in congenital fibrosis of extraocular muscles due to mutations in KIF21A."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In affected subjects, MRI demonstrated atrophy of the levator palpebrae
      superioris and superior rectus EOMs and small or absent orbital motor
      nerves. The oculomotor nerve was most severely hypoplastic, but the
      abducens was also affected.
    explanation: >-
      Genotyped in vivo imaging confirms hypoplastic ocular motor nerves and
      extends the lesion to the abducens.
  downstream:
  - target: Denervation-Driven Extraocular Muscle Maldevelopment and Fibrosis
    causal_link_type: DIRECT
    description: >-
      Extraocular muscles that never receive normal innervation fail to develop
      and become atrophic and fibrotic - the secondary event that gave the
      disorder its misleading name.
    evidence:
    - reference: PMID:15671279
      reference_title: "Magnetic resonance imaging evidence for widespread orbital dysinnervation in congenital fibrosis of extraocular muscles due to mutations in KIF21A."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        These findings suggest that neuronal disease is primary in CFEOM1, with
        myopathy arising secondary to abnormal innervation and minimal rectus
        pulley abnormality secondary to reduced EOM forces.
      explanation: >-
        States the causal direction this edge encodes: neurogenic primary
        lesion, myopathy secondary.
- name: Denervation-Driven Extraocular Muscle Maldevelopment and Fibrosis
  biological_scale: TISSUE
  description: >-
    Deprived of their motor innervation during development, the affected
    extraocular muscles - most consistently the levator palpebrae superioris and
    superior rectus - are hypoplastic and atrophic, show increased internal
    nuclei and central mitochondrial clumping, and are progressively replaced by
    fibrous connective tissue. The muscles become mechanically restrictive, which
    is why forced duction testing is positive and why the ophthalmoplegia is
    restrictive rather than simply paralytic. Because the fibrosis is a
    consequence of denervation rather than a primary myopathy, no myopathic
    therapy addresses it.
  biological_processes:
  - preferred_term: extraocular skeletal muscle development
    term:
      id: GO:0002074
      label: extraocular skeletal muscle development
    modifier: DECREASED
  - preferred_term: skeletal muscle atrophy
    term:
      id: GO:0014732
      label: skeletal muscle atrophy
    modifier: INCREASED
  - preferred_term: collagen fibril organization in the fibrotic muscle
    term:
      id: GO:0030199
      label: collagen fibril organization
    modifier: INCREASED
  cell_types:
  - preferred_term: extraocular skeletal muscle fiber
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  - preferred_term: fibroblast
    term:
      id: CL:0000057
      label: fibroblast
  evidence:
  - reference: PMID:9066352
    reference_title: "Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In addition, increased numbers of internal nuclei and central
      mitochondrial clumping are found in other extraocular muscles, suggesting
      that the muscle pathology extends beyond the muscles innervated by the
      superior division of cranial nerve III.
    explanation: >-
      Documents the secondary myopathic changes and their extent beyond the
      denervated superior-division muscles.
  - reference: PMID:9066352
    reference_title: "Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It has been generally thought that these clinical abnormalities result
      from myopathic fibrosis of the extraocular muscles.
    explanation: >-
      Names the primary-myopathy model that the same study's neuropathology
      refutes, establishing the fibrosis as secondary.
  downstream:
  - target: Restrictive Non-Progressive Ophthalmoplegia with Ptosis
    causal_link_type: DIRECT
    description: >-
      Hypoplastic, fibrotic and mechanically tethered extraocular muscles fix
      the globe and prevent elevation, and a denervated levator produces ptosis.
    evidence:
    - reference: PMID:9066352
      reference_title: "Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Congenital fibrosis of the extraocular muscles is an autosomal dominant
        congenital disorder characterized by bilateral ptosis, restrictive
        external ophthalmoplegia with the eyes partially or completely fixed in
        an infraducted (downward) and strabismic position, and markedly limited
        and aberrant residual eye movements.
      explanation: >-
        Ties the muscle lesion to the defining restrictive ophthalmoplegia and
        ptosis.
- name: Aberrant Reinnervation of Extraocular Muscles
  biological_scale: TISSUE
  description: >-
    Denervated extraocular muscles are secondarily and inappropriately
    reinnervated by misrouted branches of the surviving oculomotor nerve, most
    characteristically the lateral rectus. Because the aberrantly supplied muscle
    now fires with its new parent nerve rather than with its normal partner, the
    eye makes paradoxical, synkinetic movements - upshoots and downshoots on
    attempted adduction, A-pattern deviation, and in the rarest form synergistic
    divergence, in which attempted adduction produces abduction of both eyes.
    This is the same aberrant-reinnervation logic that produces globe retraction
    in Duane retraction syndrome.
  biological_processes:
  - preferred_term: aberrant motor neuron axon guidance to extraocular muscle
    term:
      id: GO:0008045
      label: motor neuron axon guidance
    modifier: DYSREGULATED
  - preferred_term: neuromuscular junction development at the misinnervated muscle
    term:
      id: GO:0007528
      label: neuromuscular junction development
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:15671279
    reference_title: "Magnetic resonance imaging evidence for widespread orbital dysinnervation in congenital fibrosis of extraocular muscles due to mutations in KIF21A."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Orbital imaging in CFEOM1 due to various amino acid substitutions in the
      kinesin KIF21A demonstrates consistent abnormalities of motor and sensory
      innervation in the orbit.
    explanation: >-
      Establishes consistent aberrant orbital innervation in genotyped CFEOM1.
  - reference: PMID:34081534
    reference_title: "Axonal Growth Abnormalities Underlying Ocular Cranial Nerve Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Additionally, when one nerve is absent, its normal target muscles attract
      other motor neurons.
    explanation: >-
      States the mechanism by which denervated extraocular muscles recruit
      aberrant innervation from a surviving nerve.
  downstream:
  - target: Restrictive Non-Progressive Ophthalmoplegia with Ptosis
    causal_link_type: DIRECT
    description: >-
      Synkinetic co-firing of aberrantly innervated muscles adds the aberrant
      residual eye movements that accompany the restriction.
    evidence:
    - reference: PMID:9066352
      reference_title: "Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        markedly limited and aberrant residual eye movements
      explanation: >-
        Names the aberrant residual movements attributable to misinnervation.
- name: Commissural and Corticospinal Axon Guidance Failure
  biological_scale: TISSUE
  description: >-
    In the TUBB3 and TUBB2B subtypes the tubulin lesion is not confined to the
    ocular motor nerves. Long-range projection axons are also misrouted,
    producing dysgenesis of the corpus callosum, anterior commissure, and
    corticospinal tracts, and, for the TUBB2B E421K allele, polymicrogyria
    alongside the CFEOM. This arm is what converts an isolated eye movement
    disorder into a syndromic tubulinopathy, and it is the reason CFEOM3 carries
    the extraocular features that CFEOM1 does not.
  biological_processes:
  - preferred_term: axon guidance of commissural and corticospinal projections
    term:
      id: GO:0007411
      label: axon guidance
    modifier: DYSREGULATED
  cell_types:
  - preferred_term: callosal projection neuron
    term:
      id: CL:0000540
      label: neuron
  evidence:
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neuroimaging reveals a spectrum of abnormalities including hypoplasia of
      oculomotor nerves and dysgenesis of the corpus callosum, anterior
      commissure, and corticospinal tracts.
    explanation: >-
      Documents the commissural and corticospinal dysgenesis that accompanies
      the ocular lesion in TUBB3 disease.
  - reference: PMID:23001566
    reference_title: "An inherited TUBB2B mutation alters a kinesin-binding site and causes polymicrogyria, CFEOM and axon dysinnervation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Diffusion tensor imaging of brains of affected family members reveals
      aberrations in the trajectories of commissural projection neurons,
      implying a paucity of homotopic connections.
    explanation: >-
      Human diffusion imaging shows the commissural misrouting in the TUBB2B
      CFEOM family.
- name: Restrictive Non-Progressive Ophthalmoplegia with Ptosis
  biological_scale: ORGANISM
  description: >-
    The clinical endpoint of the cascade. The eyes are held in a fixed, usually
    infraducted position and cannot be raised above the horizontal midline,
    ocular ductions are severely restricted in all directions, and there is
    bilateral blepharoptosis with poor levator function. The deficit is present
    from birth and does not progress, which distinguishes it from the acquired
    and progressive external ophthalmoplegias. Because both eyes are effectively
    immobile, patients adopt a compensatory chin-up head posture to see through
    the small residual field of gaze, and are at risk of amblyopia and exposure
    keratopathy.
  evidence:
  - reference: PMID:31313749
    reference_title: "Congenital fibrosis of the extraocular muscles: review of recent literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Congenital fibrosis of the extraocular muscles (CFEOM) is caused by
      abnormal development of the innervation of extraocular muscles.
    explanation: >-
      A contemporary review states the neurogenic causal direction that this
      chain encodes.
  - reference: PMID:16365788
    reference_title: "Recurrent mutation of the KIF21A gene in Japanese patients with congenital fibrosis of the extraocular muscles."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Clinically, each patient had congenital bilateral ptosis, an infraducted
      primary position of each eye, and the inability to raise either eye above
      midline.
    explanation: >-
      Describes the stereotyped clinical endpoint in genotyped patients.
phenotypes:
- name: Congenital Fibrosis of the Extraocular Muscles
  description: >-
    The defining clinical entity: congenital, non-progressive ophthalmoplegia
    with multiple extraocular muscle restrictions, ptosis, and variable
    restriction of horizontal and vertical eye movements.
  phenotype_term:
    preferred_term: Congenital fibrosis of extraocular muscles
    term:
      id: HP:0001491
      label: Congenital fibrosis of extraocular muscles
    temporality: CHRONIC
  evidence:
  - reference: PMID:9066352
    reference_title: "Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Congenital fibrosis of the extraocular muscles is an autosomal dominant
      congenital disorder characterized by bilateral ptosis, restrictive
      external ophthalmoplegia with the eyes partially or completely fixed in an
      infraducted (downward) and strabismic position, and markedly limited and
      aberrant residual eye movements.
    explanation: >-
      States the defining clinical syndrome of congenital restrictive
      ophthalmoplegia with ptosis.
- name: Bilateral Congenital Ptosis
  description: >-
    Severe bilateral blepharoptosis with poor levator function, present from
    birth. It reflects denervation and hypoplasia of the levator palpebrae
    superioris supplied by the superior division of the oculomotor nerve, and it
    compounds the visual deficit produced by the immobile eyes.
  phenotype_term:
    preferred_term: Ptosis
    term:
      id: HP:0000508
      label: Ptosis
  evidence:
  - reference: PMID:15671279
    reference_title: "Magnetic resonance imaging evidence for widespread orbital dysinnervation in congenital fibrosis of extraocular muscles due to mutations in KIF21A."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Subjects with CFEOM1 had severe bilateral blepharoptosis, limited
      supraduction, and variable ophthalmoplegia.
    explanation: >-
      Documents severe bilateral ptosis in a genotyped CFEOM1 cohort.
- name: Restrictive External Ophthalmoplegia
  description: >-
    Severe limitation of ocular ductions in all directions, classically with
    inability to elevate either eye above the horizontal midline. Forced duction
    testing is positive because the denervated muscles are mechanically
    restrictive, distinguishing this from a purely paralytic ophthalmoplegia.
  phenotype_term:
    preferred_term: External ophthalmoplegia
    term:
      id: HP:0000544
      label: External ophthalmoplegia
    clinical_course: STABLE
  evidence:
  - reference: PMID:16365788
    reference_title: "Recurrent mutation of the KIF21A gene in Japanese patients with congenital fibrosis of the extraocular muscles."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Clinically, each patient had congenital bilateral ptosis, an infraducted
      primary position of each eye, and the inability to raise either eye above
      midline.
    explanation: >-
      Documents the restricted ductions and fixed infraducted position in
      genotyped CFEOM1 patients.
  - reference: PMID:14597037
    reference_title: "A novel PHOX2A/ARIX mutation in an Iranian family with congenital fibrosis of extraocular muscles type 2 (CFEOM2)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The two affected siblings had bilateral ptosis and exotropia and severe
      limitation of all extraocular movements.
    explanation: >-
      Confirms the same severe restriction of all ductions in the recessive
      CFEOM2 subtype.
- name: Strabismus
  description: >-
    Ocular misalignment is universal, but its direction is subtype-dependent: the
    eyes are typically fixed in an infraducted and strabismic position in
    CFEOM1, whereas an exotropic primary position is characteristic of CFEOM2.
  phenotype_term:
    preferred_term: Strabismus
    term:
      id: HP:0000486
      label: Strabismus
  evidence:
  - reference: PMID:9066352
    reference_title: "Oculomotor nerve and muscle abnormalities in congenital fibrosis of the extraocular muscles."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      restrictive external ophthalmoplegia with the eyes partially or completely
      fixed in an infraducted (downward) and strabismic position
    explanation: >-
      Documents the fixed strabismic position of the eyes.
- name: Exotropia
  subtype: CFEOM2
  description: >-
    Divergent ocular deviation. An exotropic rather than infraducted primary
    position is the clinical marker that separates CFEOM2 from CFEOM1, and
    A-pattern exotropia also emerges after inferior rectus recession in CFEOM1.
  phenotype_term:
    preferred_term: Exotropia
    term:
      id: HP:0000577
      label: Exotropia
  evidence:
  - reference: PMID:14597037
    reference_title: "A novel PHOX2A/ARIX mutation in an Iranian family with congenital fibrosis of extraocular muscles type 2 (CFEOM2)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The two affected siblings had bilateral ptosis and exotropia and severe
      limitation of all extraocular movements.
    explanation: >-
      Documents exotropia in molecularly confirmed CFEOM2 siblings.
- name: Third Cranial Nerve Hypoplasia
  description: >-
    Hypoplasia or absence of the oculomotor nerve, the structural correlate of
    the disorder. Demonstrated at autopsy as absence of the superior division and
    its motor neurons, and in vivo by high-resolution orbital MRI and by
    neuroimaging in TUBB3 disease.
  phenotype_term:
    preferred_term: Third cranial nerve hypoplasia
    term:
      id: HP:6000597
      label: Third cranial nerve hypoplasia
  evidence:
  - reference: PMID:15671279
    reference_title: "Magnetic resonance imaging evidence for widespread orbital dysinnervation in congenital fibrosis of extraocular muscles due to mutations in KIF21A."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The oculomotor nerve was most severely hypoplastic, but the abducens was
      also affected.
    explanation: >-
      Directly reports oculomotor nerve hypoplasia on orbital MRI in genotyped
      CFEOM1.
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neuroimaging reveals a spectrum of abnormalities including hypoplasia of
      oculomotor nerves and dysgenesis of the corpus callosum, anterior
      commissure, and corticospinal tracts.
    explanation: >-
      Confirms oculomotor nerve hypoplasia in the TUBB3 (CFEOM3) subtype.
- name: Sixth Cranial Nerve Hypoplasia
  description: >-
    The abducens nerve is also small or absent on orbital MRI in CFEOM1, showing
    that the dysinnervation is not restricted to the oculomotor nerve and
    accounting for the horizontal as well as vertical duction deficits.
  phenotype_term:
    preferred_term: Sixth cranial nerve hypoplasia
    term:
      id: HP:6000596
      label: Sixth cranial nerve hypoplasia
  evidence:
  - reference: PMID:15671279
    reference_title: "Magnetic resonance imaging evidence for widespread orbital dysinnervation in congenital fibrosis of extraocular muscles due to mutations in KIF21A."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The oculomotor nerve was most severely hypoplastic, but the abducens was
      also affected.
    explanation: >-
      Reports abducens involvement alongside the oculomotor nerve in genotyped
      CFEOM1.
- name: Compensatory Chin-Up Head Posture
  description: >-
    Because the eyes are fixed below the horizontal midline, the head is
    extended (chin elevated) to bring the target into the small usable field of
    gaze. Relief of this posture, rather than restoration of motility, is the
    principal goal of inferior rectus recession.
  phenotype_term:
    preferred_term: Compensatory head posture
    term:
      id: HP:0031705
      label: Compensatory head posture
  evidence:
  - reference: PMID:31848785
    reference_title: "Surgical management of pediatric patients with congenital fibrosis of the extraocular muscles."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All the cases showed bilateral ptosis and a chin-up abnormal head posture
      (AHP).
    explanation: >-
      Documents the chin-up compensatory head posture in a paediatric CFEOM
      surgical series.
- name: Refractive Error
  category: Ophthalmologic
  description: >-
    Refractive error occurs in CFEOM and is reported as variable in severity
    across affected individuals. It is curated because it is one of the two
    amblyogenic factors this entry already treats, and because the anomalous
    globe position and chronic head posture that follow the dysinnervation
    plausibly contribute to it -- though no source curated here demonstrates
    that causal step, so no downstream edge is asserted.
  phenotype_term:
    preferred_term: Refractive error
    term:
      id: HP:0000539
      label: Abnormality of refraction
  evidence:
  - reference: PMID:7724178
    reference_title: "Congenital fibrosis of the vertically acting extraocular muscles. A new group of dominantly inherited ocular fibrosis with radiologic findings."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Refractive error and amblyopia also were variable"
    explanation: >-
      Documents refractive error in the reported CFEOM cohort. No frequency band
      is asserted: "variable" describes spread, not a proportion, and per the
      frequency SOP that does not support a FrequencyEnum value.
- name: Amblyopia
  description: >-
    Amblyopia is a recognised and variable complication, driven by the
    combination of ptotic lid occlusion, ocular misalignment, and associated
    refractive error, and is a target of occlusion or penalization therapy.
  phenotype_term:
    preferred_term: Amblyopia
    term:
      id: HP:0000646
      label: Amblyopia
  evidence:
  - reference: PMID:7724178
    reference_title: "Congenital fibrosis of the vertically acting extraocular muscles. A new group of dominantly inherited ocular fibrosis with radiologic findings."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Refractive error and amblyopia also were variable.
    explanation: >-
      Reports amblyopia, of variable degree, in a dominantly inherited
      congenital ocular fibrosis pedigree.
- name: Corneal Scarring from Exposure Keratopathy
  description: >-
    An immobile, infraducted globe with an absent Bell phenomenon and poor lid
    closure leaves the cornea chronically exposed, producing superficial
    keratopathy and, in many patients, corneal scarring. This is a preventable
    cause of visual loss that is independent of the motility deficit itself.
  phenotype_term:
    preferred_term: Corneal scarring
    term:
      id: HP:0000559
      label: Corneal scarring
  evidence:
  - reference: PMID:7724178
    reference_title: "Congenital fibrosis of the vertically acting extraocular muscles. A new group of dominantly inherited ocular fibrosis with radiologic findings."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All affected members showed superficial keratopathy, many with corneal
      scarring.
    explanation: >-
      Documents superficial keratopathy in all affected members and corneal
      scarring in many.
- name: Optic Nerve Hypoplasia
  description: >-
    Subclinical but statistically robust reduction in optic nerve size on orbital
    MRI in CFEOM1, indicating that the dysinnervation extends to the sensory as
    well as the motor apparatus of the orbit.
  phenotype_term:
    preferred_term: Optic nerve hypoplasia
    term:
      id: HP:0000609
      label: Optic nerve hypoplasia
  evidence:
  - reference: PMID:15671279
    reference_title: "Magnetic resonance imaging evidence for widespread orbital dysinnervation in congenital fibrosis of extraocular muscles due to mutations in KIF21A."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Subjects with CFEOM1 exhibited subclinical but highly significant
      reduction from normal in mean optic nerve size (P < 0.001).
    explanation: >-
      Quantifies the reduction in optic nerve size that this phenotype records.
- name: Abnormal Corpus Callosum Morphology
  subtype: CFEOM3A
  description: >-
    Dysgenesis of the corpus callosum, together with the anterior commissure and
    corticospinal tracts, on neuroimaging in the TUBB3 subtype. The finding is
    dysgenesis rather than frank agenesis, and reflects misrouting of commissural
    projection axons by the same tubulin lesion that misroutes the ocular motor
    axons.
  phenotype_term:
    preferred_term: Abnormal corpus callosum morphology
    term:
      id: HP:0001273
      label: Abnormal corpus callosum morphology
  evidence:
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Neuroimaging reveals a spectrum of abnormalities including hypoplasia of
      oculomotor nerves and dysgenesis of the corpus callosum, anterior
      commissure, and corticospinal tracts.
    explanation: >-
      Reports corpus callosum dysgenesis on neuroimaging in TUBB3 disease.
- name: Polymicrogyria
  description: >-
    Cortical malformation seen with the TUBB2B E421K allele, which segregates
    with CFEOM in the same family. It marks the boundary between the pure
    dysinnervation phenotype and the wider tubulinopathy spectrum.
  phenotype_term:
    preferred_term: Polymicrogyria
    term:
      id: HP:0002126
      label: Polymicrogyria
  evidence:
  - reference: PMID:23001566
    reference_title: "An inherited TUBB2B mutation alters a kinesin-binding site and causes polymicrogyria, CFEOM and axon dysinnervation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We have identified a novel inherited heterozygous missense mutation in
      TUBB2B that results in an E421K amino acid substitution in a family who
      segregates congenital fibrosis of the extraocular muscles (CFEOM) with
      polymicrogyria.
    explanation: >-
      Documents co-segregation of polymicrogyria with CFEOM in the TUBB2B
      family.
- name: Facial Palsy
  subtype: CFEOM3A
  description: >-
    Facial weakness accompanies the ocular phenotype in a subset of TUBB3
    alleles, extending the cranial dysinnervation beyond the ocular motor nerves.
  phenotype_term:
    preferred_term: Facial palsy
    term:
      id: HP:0010628
      label: Facial palsy
  evidence:
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Each mutation causes the ocular motility disorder CFEOM3, whereas some
      also result in intellectual and behavioral impairments, facial paralysis,
      and/or later-onset axonal sensorimotor polyneuropathy.
    explanation: >-
      Lists facial paralysis among the allele-dependent extraocular features of
      TUBB3 disease.
- name: Peripheral Axonal Neuropathy
  subtype: CFEOM3A
  description: >-
    A later-onset axonal sensorimotor polyneuropathy occurs with a subset of
    TUBB3 alleles. It is the one feature of the CFEOM spectrum that is
    progressive, in contrast to the static ocular phenotype.
  phenotype_term:
    preferred_term: Peripheral axonal neuropathy
    term:
      id: HP:0003477
      label: Peripheral axonal neuropathy
  evidence:
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Each mutation causes the ocular motility disorder CFEOM3, whereas some
      also result in intellectual and behavioral impairments, facial paralysis,
      and/or later-onset axonal sensorimotor polyneuropathy.
    explanation: >-
      Documents the later-onset axonal sensorimotor polyneuropathy of some TUBB3
      alleles.
- name: Intellectual Disability
  subtype: CFEOM3A
  description: >-
    Intellectual and behavioural impairment occurs with some, but not all, TUBB3
    alleles; it is absent from CFEOM1 and is one of the features that separates
    the syndromic from the isolated forms.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Each mutation causes the ocular motility disorder CFEOM3, whereas some
      also result in intellectual and behavioral impairments, facial paralysis,
      and/or later-onset axonal sensorimotor polyneuropathy.
    explanation: >-
      Reports intellectual and behavioural impairment as an allele-dependent
      feature of TUBB3 disease.
- name: Postaxial Oligodactyly
  subtype: Tukel syndrome
  description: >-
    Postaxial (ulnar) oligodactyly of the hands, asymmetric and more severe on
    the right in the original pedigree. Its co-occurrence with restrictive
    ophthalmoplegia defines the Tukel syndrome variant.
  phenotype_term:
    preferred_term: Postaxial oligodactyly
    term:
      id: HP:0006210
      label: Postaxial oligodactyly
  evidence:
  - reference: PMID:15863670
    reference_title: "A new syndrome, congenital extraocular muscle fibrosis with ulnar hand anomalies, maps to chromosome 21qter."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The postaxial oligodactyly/oligosyndactyly of the hands was more severe on
      the right side.
    explanation: >-
      Documents postaxial oligodactyly of the hands in the Tukel syndrome
      pedigree.
- name: Syndactyly
  subtype: Tukel syndrome
  description: >-
    Oligosyndactyly of the hands accompanies the postaxial digit reduction in the
    Tukel syndrome variant.
  phenotype_term:
    preferred_term: Syndactyly
    term:
      id: HP:0001159
      label: Syndactyly
  evidence:
  - reference: PMID:15863670
    reference_title: "A new syndrome, congenital extraocular muscle fibrosis with ulnar hand anomalies, maps to chromosome 21qter."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The postaxial oligodactyly/oligosyndactyly of the hands was more severe on
      the right side.
    explanation: >-
      Records the oligosyndactyly component of the Tukel hand anomaly.
genetic:
- name: KIF21A
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: CFEOM1
  gene_term:
    preferred_term: KIF21A (anterograde kinesin motor)
    term:
      id: hgnc:19349
      label: KIF21A
  variants:
  - name: KIF21A c.2860C>T (p.Arg954Trp)
    gene:
      preferred_term: KIF21A
      term:
        id: hgnc:19349
        label: KIF21A
    type: missense variant
    description: >-
      The recurrent CFEOM1 allele, in exon 21 of the third coiled-coil stalk
      domain, found heterozygously across unrelated families of many ancestries.
      It acts by attenuating KIF21A autoinhibition, a gain of function, rather
      than by reducing protein activity.
    evidence:
    - reference: PMID:16365788
      reference_title: "Recurrent mutation of the KIF21A gene in Japanese patients with congenital fibrosis of the extraocular muscles."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        All affected members had a heterozygous mutation of the KIF21A gene in
        exon 21 (R954W).
      explanation: >-
        Documents the recurrent heterozygous exon 21 p.R954W allele.
  evidence:
  - reference: PMID:14595441
    reference_title: "Heterozygous mutations of the kinesin KIF21A in congenital fibrosis of the extraocular muscles type 1 (CFEOM1)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We show that individuals with CFEOM1 harbor heterozygous missense
      mutations in a kinesin motor protein encoded by KIF21A. We identified six
      different mutations in 44 of 45 probands.
    explanation: >-
      Establishes KIF21A as the CFEOM1 gene in 44 of 45 probands.
  - reference: PMID:16365788
    reference_title: "Recurrent mutation of the KIF21A gene in Japanese patients with congenital fibrosis of the extraocular muscles."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      All affected members had a heterozygous mutation of the KIF21A gene in
      exon 21 (R954W).
    explanation: >-
      Documents the recurrent exon 21 p.R954W allele shared across unrelated
      families.
  notes: >-
    The same KIF21A alleles also cause the CFEOM3B pattern, so KIF21A genotype
    does not map one-to-one onto the CFEOM1/CFEOM3 clinical classification.
- name: PHOX2A
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: CFEOM2
  gene_term:
    preferred_term: PHOX2A (ARIX; nIII/nIV homeodomain transcription factor)
    term:
      id: hgnc:691
      label: PHOX2A
  variants:
  - name: PHOX2A c.439C>T (p.Gln90Ter)
    gene:
      preferred_term: PHOX2A
      term:
        id: hgnc:691
        label: PHOX2A
    type: nonsense variant
    description: >-
      Homozygous nonsense allele truncating PHOX2A at the start of the
      homeodomain, reported in an Iranian CFEOM2 family. It joins the
      splice-disrupting and brachyury-like-domain missense alleles of the
      original CFEOM2 pedigrees as a loss-of-function change.
    evidence:
    - reference: PMID:14597037
      reference_title: "A novel PHOX2A/ARIX mutation in an Iranian family with congenital fibrosis of extraocular muscles type 2 (CFEOM2)."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The 439C-->T mutation in this family changes a glutamine to a stop codon
        (Q90X) at the beginning of the PHOX2A homeodomain region.
      explanation: >-
        Specifies the nonsense allele and its position at the homeodomain.
  evidence:
  - reference: PMID:11600883
    reference_title: "Homozygous mutations in ARIX(PHOX2A) result in congenital fibrosis of the extraocular muscles type 2."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two of the mutations are predicted to disrupt splicing, whereas the third
      alters an amino acid within the conserved brachyury-like domain.
    explanation: >-
      Characterises the loss-of-function nature of the CFEOM2 PHOX2A alleles.
  - reference: PMID:14597037
    reference_title: "A novel PHOX2A/ARIX mutation in an Iranian family with congenital fibrosis of extraocular muscles type 2 (CFEOM2)."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It confirms PHOX2A as the autosomal recessive CFEOM2 disease gene and
      provides evidence that the phenotypic differences between PHOX2A mutations
      in man and mouse do not result from hypomorphic PHOX2A alleles in humans.
    explanation: >-
      Confirms PHOX2A as the recessive CFEOM2 gene through a nonsense allele.
- name: TUBB3
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: CFEOM3A
  gene_term:
    preferred_term: TUBB3 (neuron-specific beta-tubulin isotype III)
    term:
      id: hgnc:20772
      label: TUBB3
  evidence:
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We report that eight heterozygous missense mutations in TUBB3, encoding
      the neuron-specific beta-tubulin isotype III, result in a spectrum of
      human nervous system disorders that we now call the TUBB3 syndromes.
    explanation: >-
      Establishes heterozygous TUBB3 missense variants as the cause of CFEOM3
      and the wider TUBB3 syndromes.
  notes: >-
    Heterozygous missense variants are distributed across the tubulin fold. All
    reported alleles alter microtubule dynamic instability, and a subset
    additionally disrupts the microtubule-kinesin interface; that subset
    distinction tracks with whether extraocular neurological features accompany
    the CFEOM3. The broader TUBB3 syndrome spectrum, including the cortical
    malformation arm that is not part of CFEOM, is curated separately in the
    TUBB3-related Tubulinopathy entry.
- name: TUBB2B
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: TUBB2B (neuronal beta-tubulin isotype IIb)
    term:
      id: hgnc:30829
      label: TUBB2B
  variants:
  - name: TUBB2B p.Glu421Lys
    gene:
      preferred_term: TUBB2B
      term:
        id: hgnc:30829
        label: TUBB2B
    type: missense variant
    description: >-
      An inherited heterozygous substitution altering a kinesin-binding site. It
      behaves differently from the other TUBB2B alleles, which cause
      polymicrogyria without primary axon dysinnervation.
    evidence:
    - reference: PMID:23001566
      reference_title: "An inherited TUBB2B mutation alters a kinesin-binding site and causes polymicrogyria, CFEOM and axon dysinnervation."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Interestingly, by incorporating into microtubules and altering their
        dynamic properties, the E421K substitution behaves differently than
        previously identified TUBB2B substitutions, providing mechanistic
        insight into the divergence between resulting phenotypes.
      explanation: >-
        Distinguishes the CFEOM-causing E421K allele from other TUBB2B
        substitutions.
  evidence:
  - reference: PMID:23001566
    reference_title: "An inherited TUBB2B mutation alters a kinesin-binding site and causes polymicrogyria, CFEOM and axon dysinnervation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We have identified a novel inherited heterozygous missense mutation in
      TUBB2B that results in an E421K amino acid substitution in a family who
      segregates congenital fibrosis of the extraocular muscles (CFEOM) with
      polymicrogyria.
    explanation: >-
      Identifies the single TUBB2B allele that causes CFEOM rather than isolated
      polymicrogyria.
- name: COL25A1
  association: Causative
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  subtype: CFEOM5
  gene_term:
    preferred_term: COL25A1 (CLAC-P neuronal transmembrane collagen)
    term:
      id: hgnc:18603
      label: COL25A1
  evidence:
  - reference: PMID:25500261
    reference_title: "Recessive mutations in COL25A1 are a cause of congenital cranial dysinnervation disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      By using linkage analysis, candidate gene screening, and exome
      sequencing, we identified three mutations in collagen, type XXV, alpha 1
      (COL25A1) in individuals with autosomal-recessive inheritance of CCDD
      ophthalmic phenotypes.
    explanation: >-
      Establishes biallelic COL25A1 variants as a cause of recessive CCDD with a
      CFEOM phenotype.
  notes: >-
    The reported biallelic alleles reduce either the stability or the level of
    the COL25A1 protein.
diagnosis:
- name: High-resolution orbital MRI
  description: >-
    Thin-section orbital MRI demonstrates hypoplasia of the affected extraocular
    muscles together with hypoplasia and misdirection of the motor nerves that
    supply them. This is the modality that established the neurogenic basis of
    CFEOM, and so is the imaging counterpart of the causal direction this entry
    models: the nerve lesion is visible alongside the muscle lesion it causes.
  diagnosis_term:
    preferred_term: magnetic resonance imaging
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  evidence:
  - reference: PMID:34081534
    reference_title: "Axonal Growth Abnormalities Underlying Ocular Cranial Nerve Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MRI of fourteen individuals with CFEOM1 and KIF21A mutations from six families demonstrated profound hypoplasia of the SR and LPS muscles, and hypoplasia and misdirection of all the motor nerves in the orbit"
    explanation: >-
      Establishes orbital MRI as the investigation that shows both the muscle
      hypoplasia and the nerve hypoplasia and misdirection underlying it.
- name: Brain MRI for associated central malformations
  description: >-
    Brain imaging identifies the central nervous system malformations that
    accompany the tubulinopathy forms, and so contributes to distinguishing
    CFEOM3 from the more restricted CFEOM1 phenotype.
  diagnosis_term:
    preferred_term: magnetic resonance imaging
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  evidence:
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neuroimaging reveals a spectrum of abnormalities including hypoplasia of oculomotor nerves and dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts"
    explanation: >-
      Names the central malformations neuroimaging detects in the TUBB3 forms,
      which is what makes brain imaging diagnostically informative here.
- name: Exome or genome sequencing
  description: >-
    Molecular diagnosis rests on sequencing the known CFEOM genes; broader exome
    or genome sequencing is used for the substantial fraction of ocular
    congenital cranial dysinnervation disorders that remain genetically
    unsolved after targeted testing.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  evidence:
  - reference: PMID:39033378
    reference_title: "Expanding the genetics and phenotypes of ocular congenital cranial dysinnervation disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We coupled phenotyping with exome or genome sequencing of 467 probands"
    explanation: >-
      Documents exome or genome sequencing as the strategy applied to
      genetically unsolved ocular CCDD probands, the group CFEOM sits within.

treatments:
- name: Inferior Rectus Recession (Strabismus Surgery)
  description: >-
    Bilateral recession of the tight, fibrotic inferior recti to raise the eyes
    towards the horizontal midline and relieve the compensatory chin-up head
    posture. Surgery rebalances the globes mechanically; it does not restore
    innervation or ocular motility. A secondary exotropia, often A-pattern,
    emerges after inferior rectus recession because adduction is further
    weakened, so horizontal surgery is deliberately staged until the vertical
    result has declared itself.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: strabismus surgery
    term:
      id: NCIT:C15331
      label: Ophthalmologic Surgical Procedure
  target_mechanisms:
  - target: Denervation-Driven Extraocular Muscle Maldevelopment and Fibrosis
    treatment_effect: MODULATES
    description: >-
      Recession lengthens the restrictive fibrotic muscle and so relieves the
      mechanical tether, without addressing the upstream dysinnervation.
    evidence:
    - reference: PMID:31848785
      reference_title: "Surgical management of pediatric patients with congenital fibrosis of the extraocular muscles."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Bilateral IR recession in pediatric patients with CFEOM was effective in
        improving AHP, but postoperative exotropia appeared to be inevitable
        owing to the diminished adducted function caused by IR recession.
      explanation: >-
        Documents both the benefit on head posture and the mechanical trade-off
        of recessing the fibrotic muscle.
  evidence:
  - reference: PMID:31848785
    reference_title: "Surgical management of pediatric patients with congenital fibrosis of the extraocular muscles."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thus, horizontal strabismus surgery should be planned after the results of
      IR recession become evident.
    explanation: >-
      Supports the staged surgical strategy recorded in this treatment entry.
  - reference: PMID:31313749
    reference_title: "Congenital fibrosis of the extraocular muscles: review of recent literature."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Surgical management of patients with CFEOM continues to be challenging.
    explanation: >-
      A contemporary review qualifies the expected benefit of strabismus surgery
      in CFEOM.
- name: Frontalis Suspension for Ptosis
  description: >-
    Suspension of the eyelid to the frontalis muscle, typically with a silicone
    sling, to lift the ptotic lid when levator function is too poor for levator
    surgery. Lid elevation must be judged against the risk of exposure
    keratopathy, since the immobile, infraducted globe and absent Bell phenomenon
    leave the cornea vulnerable once the lid is raised.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: frontalis suspension ptosis surgery
    term:
      id: NCIT:C15331
      label: Ophthalmologic Surgical Procedure
  target_mechanisms:
  - target: Bilateral Congenital Ptosis
    treatment_effect: BYPASSES
    description: >-
      The sling substitutes frontalis action for the denervated levator
      palpebrae superioris, mechanically bypassing rather than correcting the
      dysinnervation.
    evidence:
    - reference: PMID:37364855
      reference_title: "Outcome of silicone sling frontalis suspension in children with simple congenital and complex ptosis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Complex cases included blepharophimosis epicanthus inversus syndrome (n
        = 35), Marcus Gunn jaw-winking syndrome (n = 12), oculomotor palsy (n =
        8), congenital fibrosis of extraocular muscles (n = 3), chronic
        progressive external ophthalmoplegia (n = 3), and others.
      explanation: >-
        Places CFEOM among the complex ptosis indications treated by silicone
        sling frontalis suspension in this cohort.
  evidence:
  - reference: PMID:37364855
    reference_title: "Outcome of silicone sling frontalis suspension in children with simple congenital and complex ptosis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Silicone sling FS has a favourable outcome in 70% of pediatric patients.
    explanation: >-
      Quantifies the expected outcome of the procedure in the paediatric
      population that includes CFEOM.
- name: Amblyopia and Refractive Management
  description: >-
    Spectacle correction of refractive error together with occlusion or
    penalization of the better-seeing eye. Because the motility deficit is
    static and surgically irreversible, protecting visual development is the
    part of management with the greatest effect on final acuity.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: refractive correction and amblyopia therapy
    term:
      id: NCIT:C15747
      label: Supportive Care
  target_mechanisms:
  - target: Amblyopia
    treatment_effect: MODULATES
    description: >-
      Correcting refractive error and forcing use of the amblyopic eye addresses
      the deprivational and refractive contributions to visual loss, which are
      independent of the dysinnervation itself.
    evidence:
    - reference: PMID:7724178
      reference_title: "Congenital fibrosis of the vertically acting extraocular muscles. A new group of dominantly inherited ocular fibrosis with radiologic findings."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Refractive error and amblyopia also were variable.
      explanation: >-
        Establishes refractive error and amblyopia as variable, and therefore
        individually assessable and treatable, features.
- name: Genetic Counseling
  description: >-
    Molecular testing distinguishes the autosomal dominant KIF21A, TUBB3, and
    TUBB2B subtypes from the autosomal recessive PHOX2A and COL25A1 subtypes,
    which carry very different recurrence risks, and identifies the TUBB3 and
    TUBB2B genotypes that warrant surveillance for the extraocular neurological
    features.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: genetic counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20074521
    reference_title: "Human TUBB3 mutations perturb microtubule dynamics, kinesin interactions, and axon guidance."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Each mutation causes the ocular motility disorder CFEOM3, whereas some
      also result in intellectual and behavioral impairments, facial paralysis,
      and/or later-onset axonal sensorimotor polyneuropathy.
    explanation: >-
      Allele-dependent extraocular features are the reason genotype changes
      counselling and surveillance in CFEOM.
discussions:
- discussion_id: gap_cfeom_selective_oculomotor_vulnerability
  prompt: >-
    Why do ubiquitously expressed lesions in KIF21A, TUBB3, TUBB2B, and COL25A1
    produce a phenotype largely restricted to the oculomotor and trochlear
    nerves rather than a generalised axonopathy?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#KIF21A Kinesin Autoinhibition Loss
  - pathophysiology#Beta-Tubulin Microtubule Dysfunction in Cranial Motor Neurons
  - pathophysiology#Oculomotor Axon Stalling and Aberrant Growth Cone Guidance
  rationale: >-
    KIF21A and the beta-tubulins are expressed far more widely than the ocular
    motor nuclei, yet CFEOM1 is a clinically isolated eye movement disorder. The
    mouse work names this as a selective vulnerability of the developing
    oculomotor nerve to cytoskeletal perturbation but does not explain what
    confers it, and the TUBB3 alleles that do add extraocular features show the
    restriction is allele-dependent rather than absolute. Without a mechanism
    for the selectivity, genotype-phenotype prediction across the spectrum
    remains descriptive.
  evidence:
  - reference: PMID:24656932
    reference_title: "Human CFEOM1 mutations attenuate KIF21A autoinhibition and cause oculomotor axon stalling."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      highlights a selective vulnerability of the developing oculomotor nerve to
      perturbations of the axon cytoskeleton
    explanation: >-
      Names the selective vulnerability that this gap asks to be explained.
  - reference: PMID:34081534
    reference_title: "Axonal Growth Abnormalities Underlying Ocular Cranial Nerve Disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Study of these disorders highlights the complexities of axon guidance and
      how each population of neurons uses a unique but overlapping set of axon
      guidance pathways.
    explanation: >-
      Frames the population-specific guidance repertoire that a mechanism for
      the selectivity would have to explain.
  proposed_experiments:
  - experiment_id: exp_cfeom_ocular_motor_neuron_specific_profiling
    name: Developmental-stage profiling of ocular motor versus spinal motor neurons
    description: >-
      Compare the transcriptome, cytoskeletal composition, and kinesin cargo
      complement of developing oculomotor, trochlear, abducens, and spinal motor
      neurons at the stage at which CFEOM axons stall, in wild-type and in
      Kif21a and Tubb3 knockin animals, to identify features that distinguish
      the vulnerable from the spared pools.
    decision_criterion: >-
      Identification of a factor whose loss or supplementation shifts the
      stalling phenotype between ocular motor and spared motor neuron
      populations.
    would_support:
    - pathophysiology#Oculomotor Axon Stalling and Aberrant Growth Cone Guidance
- discussion_id: gap_cfeom_mondo_myopathy_classification
  prompt: >-
    Should CFEOM continue to be classified ontologically as a myopathy of
    extraocular muscle and a progressive muscular dystrophy when the evidence
    establishes it as a non-progressive neurogenic dysinnervation disorder?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Hypoplasia of the Oculomotor and Trochlear Nerves
  - pathophysiology#Denervation-Driven Extraocular Muscle Maldevelopment and Fibrosis
  rationale: >-
    MONDO:0007614 is currently placed under both myopathy of extraocular muscle
    and progressive muscular dystrophy. Human neuropathology and genotyped
    orbital MRI both establish that the neuronal lesion is primary and the
    myopathy secondary, and every characterisation of the disorder describes it
    as non-progressive. The ontology placement therefore asserts two things the
    curated mechanism contradicts. This entry records the discrepancy rather
    than silently reclassifying; resolving it belongs upstream in MONDO.
  evidence:
  - reference: PMID:15671279
    reference_title: "Magnetic resonance imaging evidence for widespread orbital dysinnervation in congenital fibrosis of extraocular muscles due to mutations in KIF21A."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      These findings suggest that neuronal disease is primary in CFEOM1, with
      myopathy arising secondary to abnormal innervation and minimal rectus
      pulley abnormality secondary to reduced EOM forces.
    explanation: >-
      States the primary-neurogenic, secondary-myopathic ordering that conflicts
      with a myopathy or dystrophy classification.
- discussion_id: gap_cfeom_genetically_unsolved_probands
  prompt: >-
    What accounts for the majority of CFEOM and related ocular congenital
    cranial dysinnervation disorder probands who remain genetically unsolved
    after exome and genome sequencing?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Oculomotor Axon Stalling and Aberrant Growth Cone Guidance
  - pathophysiology#Hypoplasia of the Oculomotor and Trochlear Nerves
  rationale: >-
    The named CFEOM subtypes account for only part of the clinical spectrum.
    A large sequencing study of previously unsolved ocular CCDD pedigrees
    resolved fewer than one in ten probands and left most of the cohort without
    a pathogenic variant, so the curated gene list here is a floor rather than a
    complete account of the disorder. The locus-defined CFEOM3C subtype and the
    unmapped Tukel syndrome gene are the same gap visible from the nosological
    side.
  evidence:
  - reference: PMID:39033378
    reference_title: "Expanding the genetics and phenotypes of ocular congenital cranial dysinnervation disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Analyses elucidated phenotypic subgroups, identified pathogenic/likely
      pathogenic variant(s) in 43 of 467 probands (9.2%), and prioritized
      variants of uncertain significance in 70 of 467 additional probands
      (15.0%).
    explanation: >-
      Quantifies how much of the previously unsolved ocular CCDD cohort remains
      without an established genetic cause.
  - reference: PMID:39033378
    reference_title: "Expanding the genetics and phenotypes of ocular congenital cranial dysinnervation disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This study suggests that unsolved oCCDDs are clinically and genetically
      heterogeneous disorders often overlapping other Mendelian conditions and
      nominates many candidates for future replication and functional studies.
    explanation: >-
      States that the residual cohort is heterogeneous and overlaps other
      Mendelian conditions, which is why the gap is not closed by one gene.
  proposed_experiments:
  - experiment_id: exp_cfeom_noncoding_and_functional_replication
    name: Non-coding and functional replication of prioritized oCCDD candidates
    description: >-
      Extend sequencing of unsolved CFEOM pedigrees beyond protein-coding
      regions to regulatory and structural variation affecting the established
      axon-guidance genes, and functionally test prioritized candidate variants
      in ocular motor neuron models for the stalling and misrouting phenotype.
    decision_criterion: >-
      Replication of a candidate gene or regulatory variant in independent
      pedigrees together with a reproducible ocular motor axon phenotype in a
      model system.
    would_support:
    - pathophysiology#Oculomotor Axon Stalling and Aberrant Growth Cone Guidance
datasets: []

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References & Deep Research