Congenital fibrosis of the extraocular muscles

Challenges in management of congenital enophthalmos due to anomalous accessory orbital extraocular muscle bands

INTRODUCTION

Congenital enophthalmos is a rare condition characterized by posterior displacement of the globe, often associated with bony orbital anomalies or whole globe development defects. The purpose of this report is to present two unrelated cases of congenital enophthalmos secondary to anomalous accessory orbital bands and to describe characteristics of orbital imaging that differentiate this condition from the other causes.

METHODS

The case records of two patients who presented with congenital enophthalmos and were discovered to have anomalous accessory orbital extraocular muscle bands were reviewed. The clinical features, initial diagnosis, high resolution magnetic resonance imaging (MRI) findings, and surgical outcomes were noted. A 3-dimensional reconstruction model was used to understand the approach and surgical management in one of the cases.

RESULTS

Both patients presented with unilateral severe enophthalmos, globe retraction, and restricted ocular motility in all directions since birth. High-resolution MRI of the orbits revealed a short anomalous band, isointense to the muscle, arising from a rectus muscle belly and attaching to the posteroinferior part of the globe adjacent to the optic nerve. The caliber of the extraocular muscles and ocular motor nerves was normal. In one patient, surgery was not pursued due to the extreme posterior location of the band with proximity to the optic nerve. In the other patient, the deviation did not improve, despite successfully severing the accessory band, due to extensive scarring.

CONCLUSION

Anomalous accessory orbital extraocular muscle bands are a rare and often overlooked cause of congenital enophthalmos when associated with limited ocular motility. Imaging the orbit can aid in diagnosis and help differentiate it from other causes. Safe surgical approaches to address the problem are limited, and available approaches may not be effective. These two cases highlight that the management of accessory extraocular muscle bands causing enophthalmos can be extremely challenging and difficult to improve even with intensive surgical intervention.

Congenital cranial dysinnervation disorder with homozygous KIF26A variant

Congenital fibrosis of the extraocular muscles (CFEOM) type 1 is associated with heterozygous missense variants in KIF21A, which encodes a kinesin-like motor protein. Individuals with CFEOM1 have severe paralysis of upgaze and ptosis, resulting in a pronounced chin-up head posture. There can also be limitations of horizontal eye movements. Loss of function of KIF26A, an unconventional kinesin motor protein that lacks ATP-dependent motor activity, has been recently reported to cause a spectrum of congenital brain malformations associated with defects in migration, localization, and growth of excitatory neurons. It has also been associated with megacolon resembling Hirschsprung's disease. We report the case of a boy with homozygous loss of function of KIF26A with restricted eye movements, specifically restricted upgaze and downgaze with variable nystagmus and dissociated vertical eye movements. This case represents a congenital cranial dysinnervation disorder, most similar to CFEOM, and is the first report of a congenital cranial dysinnervation disorder caused by a kinesin other than KIF21A.

Eye Muscle MRI in Myasthenia Gravis and Other Neuromuscular Disorders

INTRODUCTION

MRI of extra-ocular muscles (EOM) in patients with myasthenia gravis (MG) could aid in diagnosis and provide insights in therapy-resistant ophthalmoplegia. We used quantitative MRI to study the EOM in MG, healthy and disease controls, including Graves' ophthalmopathy (GO), oculopharyngeal muscular dystrophy (OPMD) and chronic progressive external ophthalmoplegia (CPEO).

METHODS

Twenty recently diagnosed MG (59±19yrs), nineteen chronic MG (51±16yrs), fourteen seronegative MG (57±9yrs) and sixteen healthy controls (54±13yrs) were included. Six CPEO (49±14yrs), OPMD (62±10yrs) and GO patients (44±12yrs) served as disease controls. We quantified muscle fat fraction (FF), T2water and volume. Eye ductions and gaze deviations were assessed by synoptophore and Hess-charting.

RESULTS

Chronic, but not recent onset, MG patients showed volume increases (e.g. superior rectus and levator palpebrae [SR+LPS] 985±155 mm3 compared to 884±269 mm3 for healthy controls, p < 0.05). As expected, in CPEO volume was decreased (e.g. SR+LPS 602±193 mm3, p < 0.0001), and in GO volume was increased (e.g. SR+LPS 1419±457 mm3, p < 0.0001). FF was increased in chronic MG (e.g. medial rectus increased 0.017, p < 0.05). In CPEO and OPMD the FF was more severely increased. The severity of ophthalmoplegia did not correlate with EOM volume in MG, but did in CPEO and OPMD. No differences in T2water were found.

INTERPRETATION

We observed small increases in EOM volume and FF in chronic MG compared to healthy controls. Surprisingly, we found no atrophy in MG, even in patients with long-term ophthalmoplegia. This implies that even long-term ophthalmoplegia in MG does not lead to secondary structural myopathic changes precluding functional recovery.

Clinical and imaging clues to the diagnosis and follow-up of ptosis and ophthalmoparesis

Ophthalmoparesis and ptosis can be caused by a wide range of rare or more prevalent diseases, several of which can be successfully treated. In this review, we provide clues to aid in the diagnosis of these diseases, based on the clinical symptoms, the involvement pattern and imaging features of extra-ocular muscles (EOM). Dysfunction of EOM including the levator palpebrae can be due to muscle weakness, anatomical restrictions or pathology affecting the innervation. A comprehensive literature review was performed to find clinical and imaging clues for the diagnosis and follow-up of ptosis and ophthalmoparesis. We used five patterns as a framework for differential diagnostic reasoning and for pattern recognition in symptomatology, EOM involvement and imaging results of individual patients. The five patterns were characterized by the presence of combination of ptosis, ophthalmoparesis, diplopia, pain, proptosis, nystagmus, extra-orbital symptoms, symmetry or fluctuations in symptoms. Each pattern was linked to anatomical locations and either hereditary or acquired diseases. Hereditary muscle diseases often lead to ophthalmoparesis without diplopia as a predominant feature, while in acquired eye muscle diseases ophthalmoparesis is often asymmetrical and can be accompanied by proptosis and pain. Fluctuation is a hallmark of an acquired synaptic disease like myasthenia gravis. Nystagmus is indicative of a central nervous system lesion. Second, specific EOM involvement patterns can also provide valuable diagnostic clues. In hereditary muscle diseases like chronic progressive external ophthalmoplegia (CPEO) and oculo-pharyngeal muscular dystrophy (OPMD) the superior rectus is often involved. In neuropathic disease, the pattern of involvement of the EOM can be linked to specific cranial nerves. In myasthenia gravis this pattern is variable within patients over time. Lastly, orbital imaging can aid in the diagnosis. Fat replacement of the EOM is commonly observed in hereditary myopathic diseases, such as CPEO. In contrast, inflammation and volume increases are often observed in acquired muscle diseases such as Graves' orbitopathy. In diseases with ophthalmoparesis and ptosis specific patterns of clinical symptoms, the EOM involvement pattern and orbital imaging provide valuable information for diagnosis and could prove valuable in the follow-up of disease progression and the understanding of disease pathophysiology.

Congenital Fibrosis of the Extraocular Muscles: An Overview from Genetics to Management

Congenital fibrosis of the extraocular muscles (CFEOM) is a genetic disorder belonging to the congenital cranial dysinnervation disorders and is characterized by nonprogressive restrictive ophthalmoplegia. It is phenotypically and genotypically heterogeneous. At least seven causative genes and one locus are responsible for the five subtypes, named CFEOM-1 to CFEOM-5. This review summarizes the currently available molecular genetic findings and genotype–phenotype correlations, as well as the advances in the management of CFEOM. We propose that the classification of the disorder could be optimized to provide better guidance for clinical interventions. Finally, we discuss the future of genetic-diagnosis-directed studies to better understand such axon guidance disorders.

A Novel De Novo TUBB3 Variant Causing Developmental Delay, Epilepsy and Mild Ophthalmological Symptoms in a Chinese Child

Heterozygous missense mutations in TUBB3 have been implicated in various neurological disorders encompassing either isolated congenital fibrosis of the extraocular muscles type 3 (CFEOM3) or complex cortical dysplasia with other brain malformations 1 (CDCBM1). The description of seizures in patients with TUBB3 mutations is rare. Here, we reported a patient who had febrile seizures before and focal seizure this time, which was diagnosed as epilepsy in combination with an abnormal EEG. MRI showed hypoplastic corpus callosum. Mutation analysis showed a novel de novo heterozygous variant of the TUBB3 gene (NM_006086), c.763G > A (p.V255I). The patient had global developmental delay, photophobia and elliptic pupils, but lacking extraocular muscle involvement and malformations of cortical development, which might be a less severe phenotype of TUBB3 mutations. This is the first report of elliptic pupils in a patient with TUBB3 mutations and expands the spectrum of TUBB3 phenotypes. It indicates that the phenotypic range of TUBB3 mutations might exist on more of a continuum than as a discrete entity, with severity ranging from mild to severe. Further studies are needed to elucidate the complete spectrum of TUBB3-related phenotypes.

Anomalous superior oblique muscles and tendons in congenital fibrosis of the extraocular muscles

PURPOSE

To evaluate the finding of anomalous superior oblique muscles in congenital fibrosis of the extraocular muscles (CFEOM), a feature not previously emphasized in this condition.

METHODS

The medical records of all patients clinically or genetically diagnosed with CFEOM at Boston Children's Hospital between 2010 and 2018 were reviewed retrospectively. Those who underwent strabismus surgery during the study period were included in the analysis. Baseline patient characteristics, type of CFEOM, results of genetic testing, and intraoperative features of the superior oblique muscle or tendon were recorded.

RESULTS

Of 24 patients identified (age range, 1 month to 62 years), 10 (42%) had genetically confirmed CFEOM, and 22 underwent strabismus surgery, 14 (64%) involving the superior oblique muscle. Of these, 7 (50%) had anomalously inserted tendons (most commonly attached nasal to the superior rectus muscle), whereas 7 (50%) had increased superior oblique muscle tension.

CONCLUSIONS

Half of CFEOM patients who underwent superior oblique surgery had abnormally inserted superior oblique tendons, and 50% had tight muscles or abnormally thin tendons, findings that have not been well-characterized in this condition. The findings suggest that abnormal insertion of the superior oblique muscles and tendons are additional features of the disease process in CFEOM that have not been described previously. These features may contribute to the severe upgaze limitation in CFEOM and highlight the importance of superior oblique tenotomy in surgical management.

Efa6 protects axons and regulates their growth and branching by inhibiting microtubule polymerisation at the cortex

Cortical collapse factors affect microtubule (MT) dynamics at the plasma membrane. They play important roles in neurons, as suggested by inhibition of axon growth and regeneration through the ARF activator Efa6 in C. elegans, and by neurodevelopmental disorders linked to the mammalian kinesin Kif21A. How cortical collapse factors influence axon growth is little understood. Here we studied them, focussing on the function of Drosophila Efa6 in experimentally and genetically amenable fly neurons. First, we show that Drosophila Efa6 can inhibit MTs directly without interacting molecules via an N-terminal 18 amino acid motif (MT elimination domain/MTED) that binds tubulin and inhibits microtubule growth in vitro and cells. If N-terminal MTED-containing fragments are in the cytoplasm they abolish entire microtubule networks of mouse fibroblasts and whole axons of fly neurons. Full-length Efa6 is membrane-attached, hence primarily blocks MTs in the periphery of fibroblasts, and explorative MTs that have left axonal bundles in neurons. Accordingly, loss of Efa6 causes an increase of explorative MTs: in growth cones they enhance axon growth, in axon shafts they cause excessive branching, as well as atrophy through perturbations of MT bundles. Efa6 over-expression causes the opposite phenotypes. Taken together, our work conceptually links molecular and sub-cellular functions of cortical collapse factors to axon growth regulation and reveals new roles in axon branching and in the prevention of axonal atrophy. Furthermore, the MTED delivers a promising tool that can be used to inhibit MTs in a compartmentalised fashion when fusing it to specifically localising protein domains.

Outcomes of strabismus surgery in genetically confirmed congenital fibrosis of the extraocular muscles

PURPOSE

To detail surgical strategy and strabismus outcomes in a genetically defined cohort of patients with congenital fibrosis of the extraocular muscles (CFEOM).

METHODS

A total of 13 patients with genetically confirmed CFEOM (via genetic testing for mutations in KIF21A, PHOX2A, and TUBB3) were retrospectively identified after undergoing strabismus surgery at Boston Children's Hospital and surgical outcomes were compared.

RESULTS

Age at first surgery ranged from 11 months to 63 years, with an average of 3 strabismus procedures per patient. Ten patients had CFEOM1, of whom 9 had the KIF21A R954W amino acid substitution and 1 had the M947T amino acid substitution. Of the 3 with CFEOM3, 2 had the TUBB3 E410K amino acid substitution, and 1 had a previously unreported E410V amino acid substitution. CFEOM1 patients all underwent at least 1 procedure to address chin-up posture. Chin-up posture improved from 24° ± 8° before surgery to 10.0° ± 8° postoperatively (P < 0.001). Three CFEOM1 patients developed exotropia after vertical muscle surgery alone; all had the R954W amino acid substitution. Postoperatively, 1 CFEOM1 patient developed a corneal ulcer. All CFEOM3 patients appeared to have underlying exposure keratopathy, successfully treated with prosthetic replacement of the ocular surface ecosystem (PROSE) lens in 2 patients.

CONCLUSIONS

CFEOM is a complex strabismus disorder for which surgical management is difficult. Despite an aggressive surgical approach, multiple procedures may be necessary to achieve a desirable surgical effect. Knowledge of the underlying genetic diagnosis may help to inform surgical management.

The emerging role of cranial nerves in shaping craniofacial development

Organs and structures of the vertebrate head perform a plethora of tasks including visualization, digestion, vocalization/communication, auditory functions, and respiration in response to neuronal input. This input is primarily derived from afferent and efferent fibers of the cranial nerves (sensory and motor respectively) and efferent fibers of the cervical sympathetic trunk. Despite their essential contribution to the function and integration of processes necessary for survival, how organ innervation is established remains poorly understood. Furthermore, while it has been appreciated for some time that innervation of organs by cranial nerves is regulated in part by secreted factors and cell surface ligands expressed by those organs, whether nerves also regulate the development of facial organs is only beginning to be elucidated. This review will provide an overview of cranial nerve development in relation to the organs they innervate, and outline their known contributions to craniofacial development, thereby providing insight into how nerves may shape the organs they innervate during development. Throughout, the interaction between different cell and tissue types will be highlighted.

Ptosis in childhood: A clinical sign of several disorders: Case series reports and literature review

Blepharoptosis (ptosis) is a common but often overlooked sign that may serve as a sign/manifestation of other conditions, ranging from a mild and purely cosmetic presentation to a severe and occasionally progressive disorder. Ptosis may show an acute onset or may manifest as a chronic disorder. Its presentation may vary: unilateral versus bilateral, progressive versus non-progressive, isolated versus complex which occurs in association with other symptoms, and congenital versus acquired (often concomitant with neuromuscular disorders).Congenital ptosis includes the isolated type-the congenital cranial dysinnervation disorders, which are further, distinguished into different subtypes such as Horner syndrome (HS), and ptosis as a sign/manifestation of various congenital malformation syndromes.In this article, we review the primary causes of ptosis occurring in childhood, and its various clinical presentations, including a short report on selected cases observed in our institution: a classical isolated familial ptosis comprising 14 members over 5 generations, 3 sibling with isolated congenital ptosis who in addition suffered by episodes of febrile seizures, a patient with Duane retraction syndrome who presented congenital skin and hair anomalies, and a girl with HS who showed a history of congenital imperforate hymen. A flowchart outlining the congenital and acquired type of ptosis and the clinical approach to the management and treatment of children with this anomaly is reported.

Ocular congenital cranial dysinnervation disorders (CCDDs): insights into axon growth and guidance

Unraveling the genetics of the paralytic strabismus syndromes known as congenital cranial dysinnervation disorders (CCDDs) is both informing physicians and their patients and broadening our understanding of development of the ocular motor system. Genetic mutations underlying ocular CCDDs alter either motor neuron specification or motor nerve development, and highlight the importance of modulations of cell signaling, cytoskeletal transport, and microtubule dynamics for axon growth and guidance. Here we review recent advances in our understanding of two CCDDs, congenital fibrosis of the extraocular muscles (CFEOM) and Duane retraction syndrome (DRS), and discuss what they have taught us about mechanisms of axon guidance and selective vulnerability. CFEOM presents with congenital ptosis and restricted eye movements, and can be caused by heterozygous missense mutations in the kinesin motor protein KIF21A or in the β-tubulin isotypes TUBB3 or TUBB2B. CFEOM-causing mutations in these genes alter protein function and result in axon growth and guidance defects. DRS presents with inability to abduct one or both eyes. It can be caused by decreased function of several transcription factors critical for abducens motor neuron identity, including MAFB, or by heterozygous missense mutations in CHN1, which encodes α2-chimaerin, a Rac-GAP GTPase that affects cytoskeletal dynamics. Examination of the orbital innervation in mice lacking Mafb has established that the stereotypical misinnervation of the lateral rectus by fibers of the oculomotor nerve in DRS is secondary to absence of the abducens nerve. Studies of a CHN1 mouse model have begun to elucidate mechanisms of selective vulnerability in the nervous system.

Structural analyses of key features in the KANK1·KIF21A complex yield mechanistic insights into the cross-talk between microtubules and the cell cortex

The cross-talk between dynamic microtubules and the cell cortex plays important roles in cell division, polarity, and migration. A critical adaptor that links the plus ends of microtubules with the cell cortex is the KANK N-terminal motif and ankyrin repeat domains 1 (KANK1)/kinesin family member 21A (KIF21A) complex. Genetic defects in these two proteins are associated with various cancers and developmental diseases, such as congenital fibrosis of the extraocular muscles type 1. However, the molecular mechanism governing the KANK1/KIF21A interaction and the role of the conserved ankyrin (ANK) repeats in this interaction are still unclear. In this study, we present the crystal structure of the KANK1·KIF21A complex at 2.1 Å resolution. The structure, together with biochemical studies, revealed that a five-helix-bundle-capping domain immediately preceding the ANK repeats of KANK1 forms a structural and functional supramodule with its ANK repeats in binding to an evolutionarily conserved peptide located in the middle of KIF21A. We also show that several missense mutations present in cancer patients are located at the interface of the KANK1·KIF21A complex and destabilize its formation. In conclusion, our study elucidates the molecular basis underlying the KANK1/KIF21A interaction and also provides possible mechanistic explanations for the diseases caused by mutations in KANK1 and KIF21A.

Congenital Orbital Fibrosis: Molecular Genetic Analysis by Whole-Exome and Mitochondrial Genome Sequencing

A 3-year-old girl presented with congenital orbital fibrosis. We performed molecular genetic analysis by whole exome and mitochondrial genome sequencing. No pathologic mutation was identified in the present case. To our best knowledge, this study presents the first report on the findings of mutational analysis of a patient with congenital orbital fibrosis.

Eyelid Dysfunction in Neurodegenerative, Neurogenetic, and Neurometabolic Disease

Eye movement abnormalities are among the earliest clinical manifestations of inherited and acquired neurodegenerative diseases and play an integral role in their diagnosis. Eyelid movement is neuroanatomically linked to eye movement, and thus eyelid dysfunction can also be a distinguishing feature of neurodegenerative disease and complements eye movement abnormalities in helping us to understand their pathophysiology. In this review, we summarize the various eyelid abnormalities that can occur in neurodegenerative, neurogenetic, and neurometabolic diseases. We discuss eyelid disorders, such as ptosis, eyelid retraction, abnormal spontaneous and reflexive blinking, blepharospasm, and eyelid apraxia in the context of the neuroanatomic pathways that are affected. We also review the literature regarding the prevalence of eyelid abnormalities in different neurologic diseases as well as treatment strategies (Table 1).

Marshall M. Parks Memorial Lecture: Ocular Motor Misbehavior in Children: Where Neuro-Ophthalmology Meets Strabismus

Clinical diagnosis has been supplemented by neuroimaging advances, genetic discoveries, and molecular research to generate new neurobiological discoveries pertaining to early maldevelopment of ocular motor control systems. In this focused review, I examine recent paradigm shifts that have transformed our understanding of pediatric ocular motor disease at the prenuclear and infranuclear levels. The pathogenesis of complex ocular motor disorders, such as paradoxical pupillary constriction to darkness, benign tonic upgaze of infancy, congenital fibrosis syndrome, and the constellation of unique eye movements that accompany Joubert syndrome, are elucidated.

Imaging of Cranial Nerves III, IV, VI in Congenital Cranial Dysinnervation Disorders

Congenital cranial dysinnervation disorders are a group of diseases caused by abnormal development of cranial nerve nuclei or their axonal connections, resulting in aberrant innervation of the ocular and facial musculature. Its diagnosis could be facilitated by the development of high resolution thin-section magnetic resonance imaging. The purpose of this review is to describe the method to visualize cranial nerves III, IV, and VI and to present the imaging findings of congenital cranial dysinnervation disorders including congenital oculomotor nerve palsy, congenital trochlear nerve palsy, Duane retraction syndrome, Möbius syndrome, congenital fibrosis of the extraocular muscles, synergistic divergence, and synergistic convergence.

Kinesin-4 KIF21B is a potent microtubule pausing factor

Microtubules are dynamic polymers that in cells can grow, shrink or pause, but the factors that promote pausing are poorly understood. Here, we show that the mammalian kinesin-4 KIF21B is a processive motor that can accumulate at microtubule plus ends and induce pausing. A few KIF21B molecules are sufficient to induce strong growth inhibition of a microtubule plus end in vitro. This property depends on non-motor microtubule-binding domains located in the stalk region and the C-terminal WD40 domain. The WD40-containing KIF21B tail displays preference for a GTP-type over a GDP-type microtubule lattice and contributes to the interaction of KIF21B with microtubule plus ends. KIF21B also contains a motor-inhibiting domain that does not fully block the interaction of the protein with microtubules, but rather enhances its pause-inducing activity by preventing KIF21B detachment from microtubule tips. Thus, KIF21B combines microtubule-binding and regulatory activities that together constitute an autonomous microtubule pausing factor.

DOI:http://dx.doi.org/10.7554/eLife.24746.001

Microtubules are tiny tubes that cells use as rails to move various cell compartments and structures to different locations within the cell. They are made of building blocks called tubulin and form extensive networks across the cell. Depending on the cell’s needs, microtubule networks can be rapidly assembled and disassembled by adding or removing tubulin subunits at the ends of individual microtubules. While a lot is known about how cells regulate the growth and shrinkage of microtubules, much less is known about the factors that can pause these processes and thus stabilize a microtubule.

Proteins belonging to the kinesin family are molecular motors that can walk along microtubules and control how microtubules grow and shrink. A kinesin known as KIF21B is found in several types of cells including neurons and immune cells and genetic alterations in this protein have been linked with several neurodegenerative diseases. KIF21B is made up of three regions: a motor domain, a stalk and a tail domain that binds to microtubules. Recent studies have suggested that this kinesin affects the ability of one end of microtubules (known as the plus end) to grow.

Here, van Riel, Rai, Bianchi et al. used a biochemical approach to investigate the activity of KIF21B. The experiments show that KIF21B can walk to the plus end of microtubules and efficiently pause growth. Small numbers of KIF21B molecules are enough to inhibit microtubule growth and this activity depends on the motor domain and the tail domain of KIF21B working together. These experiments were performed a cell-free system and so the next challenge is to investigate how KIF21B works in living cells, including neurons and immune cells.

DOI:http://dx.doi.org/10.7554/eLife.24746.002

Clinical presentation and management of congenital ptosis

Congenital ptosis is a rare condition characterized by lower positioning of the upper eyelid that is present at birth and is a clinical condition that is persistent if not treated. It may be unilateral or bilateral and may be associated with other ocular disorders or systemic conditions, including Marcus Gunn, Horner, and Duane syndromes. It is a benign condition but causes functional, cosmetic, and psychological problems in children. However, not all patients need to undergo surgery, and usually only patients at risk of amblyopia need a prompt surgical correction, while in other cases, surgery can be postponed. The grade of ptosis, the eyelid function, and the amblyopic risk are the parameters that affect the ophthalmologist’s decision on timing of surgery and the surgical technique to be used. In fact, there are several types of surgical techniques to correct a congenital ptosis, although very often more than one is needed to obtain an acceptable result. This paper reviews the causes of congenital ptosis and associated diseases. Particular emphasis is given to surgical management and different procedures available to correct the upper eyelid anomaly and avoid permanent damage to visual function.

Two unique TUBB3 mutations cause both CFEOM3 and malformations of cortical development

One set of missense mutations in the neuron specific beta tubulin isotype 3 (TUBB3) has been reported to cause malformations of cortical development (MCD), while a second set has been reported to cause isolated or syndromic Congenital Fibrosis of the Extraocular Muscles type 3 (CFEOM3). Because TUBB3 mutations reported to cause CFEOM had not been associated with cortical malformations, while mutations reported to cause MCD had not been associated with CFEOM or other forms of paralytic strabismus, it was hypothesized that each set of mutations might alter microtubule function differently. Here, however, we report two novel de novo heterozygous TUBB3 amino acid substitutions, G71R and G98S, in four patients with both MCD and syndromic CFEOM3. These patients present with moderately severe CFEOM3, nystagmus, torticollis, and developmental delay, and have intellectual and social disabilities. Neuroimaging reveals defective cortical gyration, as well as hypoplasia or agenesis of the corpus callosum and anterior commissure, malformations of hippocampi, thalami, basal ganglia and cerebella, and brainstem and cranial nerve hypoplasia. These new TUBB3 substitutions meld the two previously distinct TUBB3-associated phenotypes, and implicate similar microtubule dysfunction underlying both.

Brain Abnormalities in Congenital Fibrosis of the Extraocular Muscles Type 1: A Multimodal MRI Imaging Study

PURPOSE

To explore the possible brain structural and functional alterations in congenital fibrosis of extraocular muscles type 1 (CFEOM1) patients using multimodal MRI imaging.

METHODS

T1-weighted, diffusion tensor images and functional MRI data were obtained from 9 KIF21A positive patients and 19 age- and gender-matched healthy controls. Voxel based morphometry and tract based spatial statistics were applied to the T1-weighted and diffusion tensor images, respectively. Amplitude of low frequency fluctuations and regional homogeneity were used to process the functional MRI data. We then compared these multimodal characteristics between CFEOM1 patients and healthy controls.

RESULTS

Compared with healthy controls, CFEOM1 patients demonstrated increased grey matter volume in bilateral frontal orbital cortex and in the right temporal pole. No diffusion indices changes were detected, indicating unaffected white matter microstructure. In addition, from resting state functional MRI data, trend of amplitude of low-frequency fluctuations increases were noted in the right inferior parietal lobe and in the right frontal cortex, and a trend of ReHo increase (p<0.001 uncorrected) in the left precentral gyrus, left orbital frontal cortex, temporal pole and cingulate gyrus.

CONCLUSIONS

CFEOM1 patients had structural and functional changes in grey matter, but the white matter was unaffected. These alterations in the brain may be due to the abnormality of extraocular muscles and their innervating nerves. Future studies should consider the possible correlations between brain morphological/functional findings and clinical data, especially pertaining to eye movements, to obtain more precise answers about the role of brain area changes and their functional consequence in CFEOM1.

Strabismus surgery in congenital fibrosis of the extraocular muscles: a paradigm

BACKGROUND

Congenital fibrosis of extraocular muscles (CFEOM) is a rare group of disorders with variable phenotypes that result from aberrant innervation to the EOMs leading to synergistic vertical and/or horizontal deviations. We report our experience with the surgical management of patients with CFEOM.

MATERIALS AND METHODS

We reviewed the clinical findings, the surgical management, and outcomes of 52 consecutive CFEOM patients operated by one surgeon at a university hospital setting between 1993 and 2014. Patients were divided into CFEOM1, 2, or 3 based on clinical and/or molecular genetic findings.

RESULTS

Thirty-seven (71.2%) cases were bilateral and 15 (28.8%) were unilateral. Six of the bilateral cases had CFEOM2, and the rest of the patients had either CFEOM1 or CFEOM3. The median age at the first surgery was 10 (1-43) years. Twenty-five were females and 27 were males. Nineteen patients had previous strabismus and/or ptosis surgeries elsewhere. The mean number of operations at our center was 1.6 ± 0.7 (1-4). A temporary stay suture was used in eight patients and permanently in seven. Of the 40 patients with abnormal head position, 18 achieved excellent, 15 good, and seven poor outcomes and ocular alignment in primary position following the latest surgery was excellent in 19, good in 18, and poor in 14 of the patients, as defined in the "Methods" section of the paper.

CONCLUSIONS

Although patients with CFEOM present significant strabismus surgical challenges because of EOM dysinnervation, fibrosis, and/or heterotopia, satisfactory alignment and improvement of the head posture can be attained in a significant proportion of patients using an individually tailored surgical approach.

Rbfox proteins regulate alternative mRNA splicing through evolutionarily conserved RNA bridges

Alternative splicing (AS) enables programmed diversity of gene expression across tissues and development. We show here that binding in distal intronic regions (>500 nucleotides (nt) from any exon) by Rbfox splicing factors important in development is extensive and is an active mode of splicing regulation. Similarly to exon-proximal sites, distal sites contain evolutionarily conserved GCATG sequences and are associated with AS activation and repression upon modulation of Rbfox abundance in human and mouse experimental systems. As a proof of principle, we validated the activity of two specific Rbfox enhancers in KIF21A and ENAH distal introns and showed that a conserved long-range RNA-RNA base-pairing interaction (an RNA bridge) is necessary for Rbfox-mediated exon inclusion in the ENAH gene. Thus we demonstrate a previously unknown RNA-mediated mechanism for AS control by distally bound RNA-binding proteins.

KIF21A mRNA expression in patients with Down syndrome

Down syndrome (DS) is a chromosomal disorder caused by chromosome 21 trisomy and is the most frequent genetic cause of intellectual disability. The gene for the kinesin family member 21A (KIF21A), is a member of the kinesin superfamily involved in the anterograde fast axonal transport. In this study, we have evaluated the possible differential expression of KIF21A mRNA, by qRT-PCR, in peripheral blood leukocytes of DS subjects and it compared with the normal population. In the assumption that changes in KIF21A gene expression levels may affect the axonal transport and the development of the nervous system of subjects with DS. In the present case-control study, KIF21A gene expression was increased in 72.72 % of DS samples compared with normal subjects. This finding suggests that changes in the expression levels of KIF21A in DS subjects may affect the axonal transport and the development of the nervous system.

KIF21A-mediated axonal transport and selective endocytosis underlie the polarized targeting of NCKX2

We have previously shown that K(+)-dependent Na(+)/Ca(2+) exchanger (NCKX) is a major calcium clearance mechanism at the large axon terminals of central neurons, whereas their somata display little NCKX activity. We investigated mechanisms underlying the axonal polarization of NCKX2 in rat hippocampal neurons. We identified NCKX2 as the first neuron-specific cargo molecule of kinesin family member 21A (KIF21A). The intracellular loop of NCKX2 specifically interacted with the WD-40 repeats, a putative cargo-binding domain, of KIF21A. Dominant-negative mutant or depletion of KIF21A inhibited the transport of NCKX2-GFP to axon fibers. Knockdown of KIF21A caused calcium dysregulation at axonal boutons but not at somatodendritic regions. Despite the axonal polarization of the NCKX activity, both somatodendritic and axonal regions were immunoreactive to NCKX2. The surface expression of NCKX2 revealed by live-cell immunocytochemistry, however, displayed highly polarized distribution to the axon. Inhibition of endocytosis increased the somatodendritic surface NCKX2 and thus abolished the axonal polarization of surface NCKX2. These results indicate that KIF21A-mediated axonal transport and selective somatodendritic endocytosis underlie the axonal polarized surface expression of NCKX2.

Management of vertical ocular deviations secondary to restrictive conditions

BACKGROUND AND PURPOSE

Management of vertical strabismus secondary to restrictive conditions can be challenging for both the patient and practitioner. The purpose of this paper is to identify both common and uncommon causes of vertical restrictive strabismus, to discuss the evaluation of these conditions, and to briefly review the etiology and recommendations for surgical management.

METHOD

Current literature was reviewed as well as the surgical techniques that have been found to be most useful from experience over the past twenty years of practice.

CONCLUSION

Surgical realignment and elimination of diplopia is both challenging and problematic. Surgery should be designed to relieve restriction, with attention to identifying and managing incomitance. Furthermore, it is important to establish realistic goals with patients.

Unilateral congenital fibrosis of the extraocular muscles with lid retraction: surgical treatment with a silicon plate on the orbital floor

Fibrosis of the extraocular muscles can be an acquired or congenital disorder (CFEOM). The congenital disorder(1) is a complex strabismus with congenital restrictive ophthalmoplegia with or without ptosis. The surgery is challenging because the eye muscles are replaced by fibrous tissue or fibrous bands and in most cases the results are not satisfactory. We present the first case report of unilateral CFEOM with palpebral adherence and hypotropia, which was managed with our technique of a silicon plate implant on the orbital floor. The purpose of the implantation of the silicon plate in the orbital floor is to improve the hypotropia caused by CFEOM.