Background

In 2002 the new term congenital cranial dysinnervation disorder (CCDD) was proposed as a substitute for the traditional concept of congenital fibrosis of the extraocular muscles based on mounting genetic, neuropathology, and imaging evidence suggesting that many, if not all, of these disorders result from a primary neurologic maldevelopment rather than from a muscle abnormality. This report provides an update eight years after that original report.

Evidence acquisition

Review of pertinent articles published from Jan 2003 until June 2010 describing CCDD variants identified under PubMed MeSH terms congenital fibrosis of the extraocular muscles, congenital cranial dysinnervation disorders, individual phenotypes included under the term CCDD, and congenital ocular motility disorders.

Results

At present a total of seven disease genes and 10 phenotypes fall under the CCDD umbrella. A number of additional loci and phenotypes still await gene elucidation, with the anticipation that more syndromes and genes will be identified in the future. Identification of genes and their function, along with advances in neuro-imaging, have expanded our understanding of the mechanisms underlying several anomalous eye movement patterns.

Conclusions

Current evidence still supports the concept that the CCDDs are primarily due to neurogenic disturbances of brainstem or cranial nerve development. Several CCDDs are now known to have non-ophthalmologic associations involving neurologic, neuroanatomic, cerebrovascular, cardiovascular, and skeletal abnormalities.

We report nine new individuals from six families who have homozygous mutations of HOXA1 with either the Bosley-Salih-Alorainy Syndrome (BSAS) or the Athabascan Brainstem Dysgenesis Syndrome (ABDS). Congenital heart disease was present in four BSAS patients, two of whom had neither deafness nor horizontal gaze restriction. Two ABDS probands had relatively mild mental retardation. These individuals blur the clinical distinctions between the BSAS and ABDS HOXA1 variants and broaden the phenotype and genotype of the homozygous HOXA1 mutation clinical spectrum.

Objective

To determine the genetic cause of Duane’s retraction syndrome (DRS) in two families segregating DRS as an autosomal dominant trait.

Method

Members of two unrelated pedigrees were enrolled in an ongoing genetic study. Linkage analysis was performed using fluorescent microsatellite markers flanking the CHN1 locus. Probands and family members were screened for CHN1 mutations.

Results

Of the six clinically affected individuals in the two pedigrees, three have bilateral and three have unilateral DRS. Both pedigrees are consistent with linkage to the DURS2 locus, one with complete and one with incomplete penetrance. Sequence analysis revealed the pedigrees segregate novel heterozygous missense CHN1 mutations, c.422C>T and c.754C>T, predicted to result in α2-chimaerin amino acid substitutions P141L and P252S, respectively.

Conclusion

Genetic analysis of two pedigrees segregating nonsyndromic DRS reveals two novel mutations in CHN1, bringing the number of DRS pedigrees know to harbor CHN1 mutations, and the number of unique CHN1 mutations, from seven to nine. Both mutations identified in this study alter residues that participate in intramolecular interactions that stabilize the inactive, closed conformation of α2-chimerin, and thus are predicted to result in its hyper-activation. Moreover, amino acid residue P252 was altered to a different residue in a previously reported DRS pedigree; thus, this is the first report of two CHN1 mutations altering the same residue, further supporting a gain-of-function etiology.

Clinical Relevance

Members of families segregating DRS as an autosomal dominant trait should be screened for mutations in the CHN1 gene, enhancing genetic counseling and permitting earlier diagnosis.

One of the biggest challenges in neuroscience is illuminating the architecture of developmental brain disorders, which include structural malformations of the brain and nerves, intellectual disability, epilepsy, as well as some psychiatric conditions like autism and potentially schizophrenia. Ongoing gene identification reveals a great diversity of genetic causes underlying abnormal brain development, illuminating new biochemical pathways often not suspected based on genetic studies in other organisms. Our greater understanding of genetic disease also shows the complexity of “allelic diversity”, in which distinct mutations in a given gene can cause a wide range of distinct diseases or other phenotypes. These diverse alleles not only provide a platform for discovery of critical protein-protein interactions in a genetic fashion, but also illuminate the likely genetic architecture of as yet poorly characterized neurological disorders.

A spectrum of neurological disorders characterized by abnormal neuronal migration, differentiation, and axon guidance and maintenance have recently been attributed to missense mutations in the genes that encode α– and β-tubulin isotypes TUBA1A, TUBA8, TUBB2B, and TUBB3, all of which putatively co-assemble into neuronal microtubules. The resulting nervous system malformations can include different types of cortical malformations, defects in commissural fiber tracts, and degeneration of motor and sensory axons. Many clinical phenotypes and brain malformations are shared among the various mutations regardless of structural location and/or isotype, while others segregate with distinct amino acids or functional domains within tubulin. Collectively, these disorders provide novel paradigms for understanding the biological functions of microtubules and their core components in normal health and disease.

Synopsis

The many functions of the microtubule cytoskeleton are essential for shaping the development and maintaining the operation of the nervous system. With the recent discovery of congenital neurological disorders that result from mutations in genes that encode different α and β-tubulin isotypes (TUBA1A, TUBB2B, TUBA8, and TUBB3), scientists have a novel paradigm to assess how select perturbations in microtubule function affect a range of cellular processes in humans. Moreover, important phenotypic distinctions found among the syndromes suggest that different tubulin isotypes can be utilized for distinct cellular functions during nervous system development. In the present paper, we review: (i) the spectrum of congenital nervous system diseases that result from mutations in tubulin and microtubule associated proteins (MAPs); (ii) the known or putative roles of these proteins during nervous system development; (iii) how the findings collectively support the “multi-tubulin” hypothesis, which postulates that different tubulin isotypes may be required for specialized microtubule functions.

Hyperactivating mutations in the CHN1 gene can cause supraduction deficits in the absence of Duane retraction syndrome.

Purpose.

Hyperactivating CHN1 mutations have been described in individuals with Duane retraction syndrome with or without vertical gaze abnormalities. This was a study of five family members with distinctive ocular dysmotility patterns that co-segregated with a novel hyperactivating CHN1 mutation.

Methods.

Participating members of a family segregating pleomorphic incomitant strabismus underwent ophthalmic examinations, and several underwent high-resolution magnetic resonance imaging (MRI) of the orbits and brain stem. Participant DNA was extracted and amplified for haplotype analysis encompassing the CHN1 region on chromosome 2q31.1, and mutation analysis of the CHN1 gene, which encodes the Rac-GAP signaling protein α2-chimaerin. In vitro functional studies of the co-inherited mutation were performed, including a Rac-GTP activation assay, quantification of α2-chimaerin translocation, and co-immunoprecipitation.

Results.

All five clinically affected family members exhibited monocular or binocular supraduction deficits, three in the absence of Duane retraction syndrome. MRI in four affected individuals demonstrated small or absent abducens nerves in all four, small oculomotor nerve in one, and small optic nerves in three. Superior oblique muscle volume was also decreased in three of the individuals, supporting trochlear nerve hypoplasia. Strabismus segregated with the CHN1 locus and affected individuals harbored a c.443A>T CHN1 mutation (p.Y148F). In vitro, this novel mutation behaved similarly to previously reported CHN1 mutations underlying familial Duane syndrome, hyperactivating α2-chimaerin by enhancing its dimerization and membrane association and lowering total intracellular Rac-GTP.

Conclusions.

Analysis of the current pedigree expands the phenotypic spectrum of hyperactivating CHN1 mutations to include vertical strabismus and supraduction deficits in the absence of Duane retraction syndrome.

Mutations producing single amino acid substitutions in neuron-specific β-tubulin isotype III cause congenital fibrosis of the extraocular muscles type 3 (CFEOM3), a variable and frequently asymmetrical congenital cranial dysinnervation disorder with ophthalmic findings that include blepharoptosis and strabismus. Magnetic resonance imaging demonstrates oculomotor and abducens nerve hypoplasia with misinnervation and secondary hypoplasia of multiple extraocular muscles and hypoplasia of the optic nerve.

Purpose.

Orbital magnetic resonance imaging (MRI) was used to investigate the structural basis of motility abnormalities in congenital fibrosis of the extraocular muscles type 3 (CFEOM3), a disorder resulting from missense mutations in TUBB3, which encodes neuron-specific β-tubulin isotype III.

Methods.

Ophthalmic examinations in 13 volunteers from four CFEOM3 pedigrees and normal control subjects, were correlated with TUBB3 mutation and MRI findings that demonstrated extraocular muscle (EOM) size, location, contractility, and innervation.

Results.

Volunteers included clinically affected and clinically unaffected carriers of R262C and D417N TUBB3 amino acid substitutions and one unaffected, mutation-negative family member. Subjects with CFEOM3 frequently had asymmetrical blepharoptosis, limited vertical duction, variable ophthalmoplegia, exotropia, and paradoxical abduction in infraduction. MRI demonstrated variable, asymmetrical levator palpebrae superioris and superior rectus EOM atrophy that correlated with blepharoptosis, deficient supraduction, and small orbital motor nerves. Additional EOMs exhibited variable hypoplasia that correlated with duction deficit, but the superior oblique muscle was spared. Ophthalmoplegia occurred only when the subarachnoid width of CN3 was <1.9 mm. A-pattern exotropia was frequent, correlating with apparent lateral rectus (LR) muscle misinnervation by CN3. Optic nerve (ON) cross sections were subnormal, but rectus pulley locations were normal.

Conclusions.

CFEOM3 caused by TUBB3 R262C and D417N amino acid substitutions features abnormalities of EOM innervation and function that correlate with subarachnoid CN3 hypoplasia, occasional abducens nerve hypoplasia, and subclinical ON hypoplasia that can resemble CFEOM1. Clinical and MRI findings in CFEOM3 are more variable than those in CFEOM1 and are often asymmetrical. Apparent LR innervation by the inferior rectus motor nerve is an overlapping feature of Duane retraction syndrome and CFEOM1. These findings suggest that CFEOM3 is an asymmetrical, variably penetrant, congenital cranial dysinnervation disorder leading to secondary EOM atrophy.

Purpose

To describe phenotypic characteristics of two pedigrees manifesting early onset crystalline cataract with mutations in the γD-crystallin gene (CRYGD).

Methods

A detailed medical history was obtained from two Caucasian pedigrees manifesting autosomal dominant congenital cataracts. Genomic DNA was extracted from saliva (DNA Genotek). Single Nucleotide Polymorphism (SNP) based genome analysis of the larger pedigree revealed linkage to an 8.2 MB region on chromosome 2q33-q35 which encompassed the crystallin-gamma gene cluster (CRYG). Exons and flanking introns of CRYGA, CRYGB, CRYGC and CRYGD were amplified and sequenced to identify disease-causing mutations.

Results

A morphologically unique cataract with extensive refractile “crystals” scattered throughout the nucleus and perinuclear cortex was found in the probands from both pedigrees. A heterozygous C→A mutation was identified at position 109 of the coding sequence (R36S of the processed protein) in exon 2 of CRYGD and this missense mutation was found to cosegregate with the disease in the larger family; this mutation was then identified in affected individuals of pedigree 2 as well.

Conclusions

The heterozygous 109C→A CRYGD missense mutation is associated with a distinct crystalline cataract in two US Caucasian pedigrees. This confirms crystalline cataract formation with this mutation, as previously reported in sporadic childhood case from the Czech Republic and in members of a Chinese family.

The HOXA1-related syndromes result from autosomal recessive truncating mutations in the homeobox transcription factor, HOXA1. Limited horizontal gaze and sensorineural deafness are the most common features; affected individuals can also have facial weakness, mental retardation, autism, motor disabilities, central hypoventilation, carotid artery and/or conotruncal heart defects. Möbius syndrome is also phenotypically heterogeneous, with minimal diagnostic criteria of nonprogressive facial weakness and impaired ocular abduction; mental retardation, autism, motor disabilities, additional eye movements restrictions, hearing loss, hypoventilation, and craniofacial, lingual, and limb abnormalities also occur. We asked, given the phenotypic overlap between these syndromes and the variable expressivity of both disorders, whether individuals with Möbius syndrome might harbor mutations in HOXA1. Our results suggest that HOXA1 mutations are not a common cause of sporadic Möbius syndrome in the general population.

Purpose

We describe the clinical phenotype of a Mexican family segregating Duane syndrome as an autosomal dominant trait linked to chromosome 2q31 (DURS2) and previously reported to harbor a heterozygous α2-chimaerinmissense mutation.

Methods

A five-generation Mexican family was analyzed. Ten affected subjects were available for clinical examination. Participating subjects were tested for visual acuity, ocular alignment by prism cover testing, ocular ductions and versions, and globe retraction. In children, alignment was measured with the Krimsky test in cardinal positions of gaze.

Results

Ten cases were included, 6 females and 4 males. Five cases presented with bilateral and 5 with unilateral Duane syndrome. Right side was the most commonly affected side on unilateral cases. Five cases exhibited exotropia, 4 esotropia, and 1 hypotropia. Seven patients had important limitation of abduction; two, moderate limitation. Four patients had mild adduction limitation and 4 had moderate limitation. No additional anomalies such as fourth (trochlear) nerve palsy, blepharoptosis, or dense amblyopia, reported in previous Duane syndrome families, were observed. All 3 cases that exhibited vertical dysfunction had upgaze limitation. One instance of nonpenetrance was recorded.

Conclusions

Considerable intrafamilial clinical variability was observed in this Duane syndrome pedigree carrying a α2-chimaerin mutation. The presence of bilateral involvement and associated vertical movements, commonly observed in this and others DURS2 families, could suggest the occurrence of CHN1 mutations as the source of the disease in isolated or familial DURS cases.

This article reviews symptoms and signs of aberrant axon connectivity in humans, and summarizes major human genetic disorders that result, or have been proposed to result, from defective axon guidance. These include corpus callosum agenesis, L1 syndrome, Joubert syndrome and related disorders, horizontal gaze palsy with progressive scoliosis, Kallmann syndrome, albinism, congenital fibrosis of the extraocular muscles type 1, Duane retraction syndrome, and pontine tegmental cap dysplasia. Genes mutated in these disorders can encode axon growth cone ligands and receptors, downstream signaling molecules, and axon transport motors, as well as proteins without currently recognized roles in axon guidance. Advances in neuroimaging and genetic techniques have the potential to rapidly expand this field, and it is feasible that axon guidance disorders will soon be recognized as a new and significant category of human neurodevelopmental disorders.

Mutations in axon guidance receptors, their ligands, and downstream signaling molecules lead to Duane syndrome and various other disorders characterized by errors in muscle innervation.

PURPOSE

To determine the molecular etiologies of Duane’s retraction syndrome (DRS), we are investigating its genetic bases. We have previously identified the transcription factors SALL4 and HOXA1 as the genes mutated in DRS with radial anomalies, and in DRS with deafness, vascular anomalies, and cognitive deficits, respectively. We know less, however, about the genetic etiology of DRS when it occurs in isolation, and only one genetic locus for isolated DRS, the DURS2 locus on chromosome 2, has been mapped to date. Toward the goal of identifying the DURS2 gene, we have ascertained and studied two pedigrees that segregate DRS as a dominant trait.

METHODS

We enrolled members of two large dominant DRS pedigrees into our ongoing study of the genetic basis of the congenital cranial dysinnervation disorders, and conducted linkage analysis to determine if their DRS phenotype maps to the DURS2 locus.

RESULTS

By haplotype analysis, the DRS phenotype in each family co-segregates with markers spanning the DURS2 region, and linkage analysis reveals maximum lod scores of >2, establishing that the DRS phenotype in these two pedigrees maps to the DURS2 locus.

CONCLUSIONS

These two pedigrees double the published pedigrees known to map to the DURS2 locus, and can thus contribute toward the search for the DURS2 gene. The affected members represent a genetically defined population of DURS2-linked DRS individuals, and hence studies of their clinical and structural features can enhance our understanding of the DURS2 phenotype, as described in the companion paper.

Purpose

Two Chinese families (XT and YT) with congenital fibrosis of the extraocular muscles (CFEOM) were identified. The purpose of this study was to determine if previously described Homo sapiens kinesin family member 21A (KIF21A) mutations were responsible for CFEOM in these two Chinese pedigrees.

Methods

Clinical characterization and genetic studies were performed. Microsatellite genotyping for linkage to the CFEOM1 and CFEOM3 loci was performed. The probands were screened for KIF21A mutations by bidirectional direct sequencing. Once a mutation was detected in the proband, all other participating family members and 100 unrelated control normal individuals were screened for the mutation.

Results

All affected individuals in family XT shared the common manifestations of CFEOM1. Family YT had two affected individuals, a mother and a daughter. The daughter had CFEOM1, while her mother never had congential ptosis but did have limited extraocular movements status post strabismus surgery. Haplotype analysis revealed that pedigree XT was linked to the 12q CFEOM1 locus and the affected memberes harbored the second most common missense mutation in KIF21A (2,861G>A, R954Q). Family YT harbored the most common missense de novo mutation in KIF21A (2,860C>T, R954W). Both of these mutations have been previously described.

Conclusions

The observation of these two KIF21A mutations in a Chinese pedigree underscores the homogeneity of these mutations as a cause of CFEOM1 and CFEOM3 across ethnic divisions.

Purpose

To summarize the clinical, neuroradiologic, and genetic observations in a group of patients with unilateral synergistic divergence (SD).

Methods

Five unrelated patients with unilateral SD underwent ophthalmologic and orthoptic examinations; three of them also had magnetic resonance imaging of the brain and orbits. Three patients underwent genetic evaluation of genes known to affect ocular motility (KIF21A, PHOX2A, HOXA1, and ROBO3).

Results

Patients did not meet clinical criteria for CFEOM types 1, 2, or 3. Each patient had severe adduction weakness on the affected side and a large angle exotropia in primary gaze that increased on attempted contralateral gaze because of anomalous abduction. Magnetic resonance imaging revealed a much smaller medial rectus muscle in the involved SD orbit. Oculomotor cranial nerves were present in the one patient imaged appropriately. Genetic sequencing in three patients revealed no mutations in KIF21A, PHOX2A, HOXA1, or ROBO3.

Conclusions

SD should be classified as a distinct congenital ocular motility pattern within congenital cranial dysinnervation disorders. It is possibly caused by denervation of the medial rectus with dysinnervation of the ipsilateral lateral rectus by the oculomotor nerve precipitated by genetic abnormalities (some currently identified) or by local environmental, teratogenic, or epigenetic disturbances.

Purpose

We employed magnetic resonance imaging (MRI) to study extraocular muscles (EOMs) and nerves in Duane-radial ray (Okihiro) syndrome (DRRS) due to mutations in the transcription factor SALL4.

Methods

We examined four male and two female affected members of a pedigree previously reported to co-segregate DRRS and a heterozygous SALL4 mutation. Coronal T1 weighted MRI of the orbits and heavily T2 weighted images in the plane of the cranial nerves were obtained in four subjects. MRI findings were correlated with motility examinations, and published norms obtained using identical technique.

Results

Five of the six subjects with DRRS had radial ray abnormalities including thumb, radial artery, radial bone, and pectoral muscle hypoplasia. Three had bi- and three unilateral ocular involvement. Seven eyes had limitation of both ab- and adduction, while two had limitation only of abduction. Most affected eyes had lid fissure narrowing and retraction in adduction. Intraorbital and intracranial abducens nerves (CN6) were small to absent, particularly ipsilateral to abduction deficiency. All cases undergoing MRI had normal intracranial oculomotor nerves (CN3). Optic nerve (ON) cross section was similar to normal. EOMs and pulleys were structurally normal in most cases. In some affected orbits, a branch of CN3 closely approximated and presumably innervated the LR.

Conclusions

DRRS has a Duane syndrome phenotype, with a variable and asymmetric endophenotype including marked CN6 hypoplasia and probable innervation or co-innervation of the LR by CN3. This endophenotype is more limited than reported in DURS2-linked Duane syndrome and CFEOM1, which are clinically similar congenital cranial dysinnervation disorders that feature, in addition, CN3 hypoplasia and more widespread EOM abnormalities.

Introduction

Möbius’ syndrome typically presents as a sporadic trait with congenital facial palsy and abduction impairment. We used high resolution magnetic resonance imaging (MRI) and genetic analysis to examine a family with features of Möbius’ syndrome.

Methods

We examined three related family members having congenital complete opthalmoplegia with ptosis and facial diplegia. Orbits were imaged in quasi-coronal and sagittal planes 2 mm thick. Subarachnoid cranial nerves were imaged in planes 1 mm thick. Linkage and mutation analysis were performed to determine if the pedigree harbored mutations in four candidate genes.

Results

In affected subjects, MRI showed marked hypoplasia of extraocular muscles and intraorbital motor nerves. In the anterior orbit, rectus extraocular muscles were less hypoplastic but markedly curved toward insertion. Oblique extraocular muscles were hypoplastic and abnormally inserted. Posterior bony orbits were hypoplastic. Optic nerves were markedly straightened. Brainstems and cranial nerves III, VI, VII, and VIII were normal bilaterally. No pathogenic mutations were detected in affected individuals.

Conclusions

Previous MRI studies have demonstrated brainstem hypoplasia and cranial nerve aplasia in Möbius’ syndrome. The current family had normal brainstems and subarachnoid portions of motor cranial nerves innervating the orbit, but marked extraocular muscle hypoplasia. These clinical and MRI findings are atypical for Möbius’ syndrome and other congenital cranial dysinnervation disorders (CCDDs). Congenital facial weakness and complete ophthalmoplegia may occur despite MRI evidence of normal brainstem anatomy. The endophenotype appears to result from a genetic defect distinct from the CCDDs defined thus far, rather than a global brainstem insult.

Purpose

To describe the ocular features and genetic mutation of a 6 month old male with congenital fibrosis of the extraocular muscles Type 1 (CFEOM1) with distinctive conjunctival changes and small intrapapillary disc colobomata.

Materials & Methods

Clinical examination of the proband, his parents and sister, with DNA mutational analysis of the proband and parents.

Results

In addition to CFEOM1, the patient had the unusual clinical findings of bilateral optic disc colobomata. Ophthalmic examination of his parents and sibling were normal. The patient but neither of his parents harbored the most common CFEOM1 mutation, 2860 C>T, in KIF21A, resulting in the R954W substitution.

Conclusion

This is the first report of bilateral optic disc colobomata in a patient with a confirmed mutation of the CFEOM1 gene.

Purpose

High-resolution magnetic resonance imaging (MRI) can now directly demonstrate innervation to extraocular muscles and quantify optic nerve size. A quantitative MRI technique was developed to study the oculomotor nerve (CN3) and applied to congenital fibrosis of extraocular muscles (CFEOM) and congenital oculomotor palsy.

Methods

The subarachnoid portions of the CN3s were imaged with a 1.5-T MRI scanner and conventional head coils, acquiring heavily T2-weighted oblique axial planes 1-mm thick and parallel to the optic chiasm. Thirteen normal subjects, 14 with CFEOM, and 3 with congenital CN3 palsy were included. Digital image analysis was used to measure CN3 diameter, which was correlated with motility findings.

Results

In CFEOM, CN3 diameter was bilaterally subnormal in eight subjects, unilaterally subnormal in three subjects, and normal in three subjects. Mean ± SD CN3 diameter in CFEOM was 1.14 ± 0.61 mm, significantly smaller than the diameter in normal subjects, which measured 2.01 ± 0.36 mm (P < 0.001). CN3 diameter variably correlated with clinical function. One subject with congenital CN3 palsy showed bilateral CN3 hypoplasia, but CN3 diameter was normal in two other subjects with congenital CN3 palsy.

Conclusions

Unilateral or bilateral hypoplasia of CN3 is quantitatively demonstrable using MRI in many cases of CFEOM and occasionally in congenital CN3 palsy. Variations in CN3 diameter in CFEOM and congenital CN3 palsy suggest mechanistic heterogeneity of these disorders that may be clarified by further imaging and genetic studies.

Purpose

High-resolution, multipositional magnetic resonance imaging (MRI) was used to demonstrate extraocular muscles (EOMs) and associated motor nerves in Duane retraction syndrome (DRS) linked to the DURS2 locus on chromosome 2.

Methods

Five male and three female affected members of two autosomal dominant DURS2 pedigrees were enrolled in the study. Coronal T1-weighted MRI of the orbits was obtained in multiple gaze positions, as well as with heavy T2 weighting in the plane of the cranial nerves. MRI findings were correlated with motility.

Results

All subjects had unilateral or bilateral limitation of abduction, or of both abduction and adduction, with palpebral fissure narrowing and globe retraction in adduction. Orbital motor nerves were typically small, with the abducens nerve (cranial nerve [CN]6) often nondetectable. Lateral rectus (LR) muscles were structurally abnormal in seven subjects, with structural and motility evidence of oculomotor nerve (CN3) innervation from vertical rectus EOMs leading to A or V patterns of strabismus in three cases. Four cases had superior oblique, two cases superior rectus, and one case levator EOM hypoplasia. Only the medial and inferior rectus and inferior oblique EOMs were spared. Two cases had small CN3s.

Conclusions

DRS linked to the DURS2 locus is associated with bilateral abnormalities of many orbital motor nerves, and structural abnormalities of all EOMs except those innervated by the inferior division of CN3. The LR may be coinnervated by CN3 branches normally destined for any other rectus EOMs. Therefore, DURS2-linked DRS is a diffuse congenital cranial dysinnervation disorder involving but not limited to CN6.

Introduction

Although the ocular motility examination has been used traditionally in the diagnosis of strabismus that is a result of cranial nerve (CN) abnormalities, magnetic resonance imaging (MRI) now permits the direct imaging of lesions in CN palsies.

Methods

Prospectively, nerves to extraocular muscles (EOMs) were imaged with T1 weighting in orbits of 83 orthotropic volunteers and 96 strabismic patients in quasicoronal planes using surface coils. Intraorbital resolution was 234–312 microns within 1.5- to 2.0-mm thick planes. CNs were imaged at the brainstem using head coils and T2 weighting, yielding 195 micron resolution in planes 1.0-mm thick in 6 normal volunteers and 22 patients who had oculomotor (CN3), trochlear (CN4), or abducens (CN6) palsies and Duane syndrome.

Results

Oculomotor (CN3) and abducens (CN6) but not trochlear (CN4) nerves were demonstrable in the orbit and skull base in all normal subjects. Patients with congenital CN3 palsies had hypoplastic CN3s both in orbit and skull base, with hypoplasia of involved EOMs. Patients with chronic CN6 and CN4 palsies exhibited atrophy of involved EOMs. Patients with Duane syndrome exhibited absence or hypoplasia of CN6 in both orbit and brainstem regions, often with mild hypoplasia and apparent misdirection of CN3 to the lateral rectus muscle. Unlike CN6 palsy, patients with Duane syndrome exhibited no EOM hypoplasia. Patients with congenital fibrosis exhibited severe hypoplasia of CN3, moderate hypoplasia of CN6, and EOM hypoplasia, particularly severe for the superior rectus and levator muscles.

Conclusion

High-resolution MRI can directly demonstrate pathology of CN3 and CN6 and affected EOM atrophy in strabismus caused by CN palsies. Direct imaging of CNs and EOMs by MRI is feasible and useful in differential diagnosis of complex strabismus.

Background

To learn about the molecular etiology of strabismus, we are studying the genetic basis of 'congenital fibrosis of the extraocular muscles' (CFEOM). These syndromes are characterized by congenital restrictive ophthalmoplegia affecting muscles in the oculomotor and trochlear nerve distribution. Individuals with the classic form of CFEOM are born with bilateral ptosis and infraducted globes. When all affected members of a family have classic CFEOM, we classify the family as a CFEOM1 pedigree. We have previously determined that a CFEOM1 gene maps to the FEOM1 locus on chromosome 12cen. We now identify additional pedigrees with CFEOM1 to determine if the disorder is genetically heterogeneous and, if so, if any affected members of CFEOM1 pedigrees or sporadic cases of classic CFEOM harbor mutations in ARIX, the CFEOM2 disease gene.

Results

Eleven new CFEOM1 pedigrees were identified. All demonstrated autosomal dominant inheritance, and nine were consistent with linkage to FEOM1. Two small CFEOM1 families were not linked to FEOM1, and both were consistent with linkage to FEOM3. We screened two CFEOM1 families consistent with linkage to FEOM2 and 5 sporadic individuals with classic CFEOM and did not detect ARIX mutations.

Conclusions

The phenotype of two small CFEOM1 families does not map to FEOM1, establishing genetic heterogeneity for this disorder. These two families may harbor mutations in the FEOM3 gene, as their phenotype is consistent with linkage to this locus. Thus far, we have not identified ARIX mutations in any affected members of CFEOM1 pedigrees or in any sporadic cases of classic CFEOM.

Background

Congenital fibrosis of the extraocular muscles type 1 (CFEOM1) is an autosomal dominant eye movement disorder linked to the pericentromere of chromosome 12 (12p11.2 - q12). Sarcospan is a member of the dystrophin associated protein complex in skeletal and extraocular muscle and maps to human chromosome 12p11.2. Mutations in the genes encoding each of the other components of the skeletal muscle sarcospan-sarcoglycan complex (α - δ sarcoglycan) have been shown to cause limb girdle muscular dystrophy (LGMD2C-F). To determine whether mutations in the sarcospan gene are responsible for CFEOM1 we: (1) attempted to map sarcospan to the CFEOM1 critical region; (2) developed a genomic primer set to directly sequence the sarcospan gene in CFEOM1 patients; and (3) generated an anti-sarcospan antibody to examine extraocular muscle biopsies from CFEOM1 patients.

Results

When tested by polymerase chain reaction, sarcospan sequence was not detected on yeast or bacterial artificial chromosomes from the CFEOM1 critical region. Sequencing of the sarcospan gene in CFEOM1 patients from 6 families revealed no mutations. Immunohistochemical studies of CFEOM1 extraocular muscles showed normal levels of sarcospan at the membrane. Finally, sarcospan was electronically mapped to bacterial artificial chromosomes that are considered to be outside of the CFEOM1 critical region.

Conclusions

In this report we evaluate sarcospan as a candidate gene for CFEOM1. We have found that it is highly unlikely that sarcospan is involved in the pathogenesis of this disease. As of yet no sarcospan gene mutations have been found to cause muscular abnormalities.