Duane's syndrome

A challenging diagnosis of narcolepsy type 2 in a patient with Duane syndrome

Duane syndrome is a form of congenital strabismus with horizontal eye movement limitation. This may present a diagnostic challenge when assessing for rapid eye movements during stage REM utilizing PSG or MSLT. We present a case of a child with Duane syndrome who presented with excessive daytime sleepiness and underwent evaluation for hypersomnia. His eye movement limitation provided a challenge in identifying stage REM. In patients with eye movement limitations or prosthetic eyes, it is necessary to look for other features of stage REM such as low chin EMG tone and EEG pattern.

Case Report: Unilateral Sixth Cranial Nerve Palsy Associated With COVID-19 in a 2-year-old Child

Children have been described to show neurological symptoms in acute coronavirus disease 2019 (COVID-19) and multisystemic inflammatory syndrome in children (MIS-C). We present a 2-year-old boy's clinical course of unilateral acute sixth nerve palsy in the context of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Onset of the palsy in the otherwise healthy boy occurred seven days after symptoms attributed to acute infection had subsided respectively 3 weeks after onset of respiratory symptoms. SARS-CoV-2 specific IgG was detected in serum as well as in cerebrospinal fluid. The patient showed a prolonged but self-limiting course with a full recovery after three and a half months. This case illustrates in a detailed chronological sequence that sixth cranial nerve involvement may occur as post-infectious, self-limiting complication of pediatric SARS-CoV-2-infection thus expanding the neurological spectrum of symptoms for children with COVID-19. Clinicians should be aware of the possibility of post-infectious sixth nerve palsy related to SARS-CoV-2-infection particularly in view of recent respiratory tract infection or confirmed cases of SARS-CoV-2-infection amongst the patient's close contacts.

Non-classical 1p36 deletion in a patient with Duane retraction syndrome: case report and literature review

Background

Monosomy of 1p36 is considered the most common terminal microdeletion syndrome. It is characterized by intellectual disability, growth retardation, seizures, congenital anomalies, and distinctive facial features that are absent when the deletion is proximal, beyond the 1p36.32 region. In patients with proximal deletions, little is known about the associated phenotype, since only a few cases have been reported in the literature. Ocular manifestations in patients with classical 1p36 monosomy are frequent and include strabismus, myopia, hypermetropia, and nystagmus. However, as of today only one patient with 1p36 deletion and Duane retraction syndrome (DRS) has been reported.

Case presentation

We describe a patient with intellectual disability, facial dysmorphism, and bilateral Duane retraction syndrome (DRS) type 1. Array CGH showed a 7.2 Mb de novo deletion from 1p36.31 to 1p36.21.

Discussion

Our patient displayed DRS, which is not part of the classical phenotype and is not a common clinical feature in 1p36 deletion syndrome; we hypothesized that this could be associated with the overlapping deletion between the distal and proximal 1p36 regions. DRS is one of the Congenital Cranial Dysinnervation Disorders, and a genetic basis for the syndrome has been extensively reported. The HES3 gene is located at 1p36.31 and could be associated with oculomotor alterations, including DRS, since this gene is involved in the development of the 3rd cranial nerve and the 6th cranial nerve’s nucleus. We propose that oculomotor anomalies, including DRS, could be related to proximal 1p36 deletion, warranting a detailed ophthalmologic evaluation of these patients.

Avoiding blindness in managing epistaxis for a child with Duane's Retraction Syndrome

Duane's Retraction Syndrome (DRS), a congenital cranial dysinnervation disorder, accounts for 5% of all strabismus. A vascular anomaly in DRS, which became clinically relevant in the context of significant epistaxis, is presented. A 15-year-old girl with DRS underwent a rhinological procedure for traumatic nasal deformity and suffered large volume epistaxis. Using angiography, an anatomical variation was identified, noting the ophthalmic artery was supplied by branches from the sphenopalatine artery, facial artery, and middle meningeal artery; not from the internal carotid artery. Hence epistaxis control was achieved via alternative methods, and unilateral blindness was avoided.

Chromosomal microarray analysis of patients with Duane retraction syndrome

PURPOSE

Duane retraction syndrome (DS) is a rare congenital strabismus with genetic heterogeneity. The genetic causes of DS are not always of monogenic origin; various chromosomal copy number variations (CNVs) have also been reported. The objective of our study was to characterize the CNVs, including gains and losses detected by high-resolution chromosomal microarray in patients with DS.

METHODS

Twenty patients with DS were investigated using high-resolution chromosomal microarray analysis (CMA) (Affymetrix CytoScan Array 750 K). Conventional cytogenetic analysis was also performed.

RESULTS

All samples revealed normal karyotype by cytogenetic analysis. However, in all our patients, multiple CNVs, including gains and losses, were detected using the high-resolution CMA method. Chromosomal loci 1q21.2, 2p11.2-q11.1, 2q21.1-q21.2, 4p16.1, 7p11.2-q11.21, 14q32.33, 17p11.2-q11.1 and 20p11.1-q11.21 were the most frequently affected regions.

CONCLUSIONS

This study emphasized that CNVs in several chromosomal regions are known to be involved in DS. We also underscore the genetic heterogeneity of DS. Our suggestion is that genes located in the most frequently affected regions should be focused on in the following candidate gene studies.

CHN1 gene mutation analysis in patients with Duane retraction syndrome

PURPOSE

To investigate CHN1 (chimerin 1) gene mutations in patients with isolated nonsyndromic Duane syndrome and accompanying positive familial history, bilaterality, or various systemic disorders.

METHODS

Patients with Duane retraction syndrome (DRS) and a positive family history of congenital ocular motility disturbance or bilateral involvement or accompanying any congenital disorder(s) seen consecutively at a single center from 2013 to 2016 were enrolled. All subjects underwent full ophthalmologic examination, including refraction, best-corrected visual acuity, ocular alignment and motility, globe retraction, and biomicroscopic or fundus evaluation. DNA samples were investigated by direct sequencing of the coding regions of the CHN1 gene.

RESULTS

A total of 30 patients (15 males) were included (mean age, 11.8 ± 10.4 years; range, 2-45 years): 8 cases presented with bilateral DRS; 22, with unilateral DRS. Family history of ocular motility abnormality was positive in 16 patients. Eleven cases had an additional congenital disorder. In 2 patients, 2 different mutations were detected in the CHN1 gene: p.E313K (c.937G>A) and p.N224S (c.671A>G).

CONCLUSIONS

CHN1 mutations were identified in 2 bilateral cases and in 1 parent of 1 affected case. One mutation is novel and occurred with additional vertical gaze abnormalities. Additional genetic studies evaluating chimerin 1 (CHN1) and its role in the development of the ocular motor axis are needed to provide new data about these mutations and phenotypic variations.

A microdeletion in the GRHL2 Gene in two unrelated patients with congenital fibrosis of the extra ocular muscles

Objective

Congenital fibrosis of the extraocular muscles type 1 (CFEOM1) is known to be caused by mutations in KIF21A or TUBB3 or other known genes (SALL4, CHN1, HOXA1). However, affected children may harbor other genetic defects. Therefore, a candidate gene analysis (KIF21A, TUBB3 SALL4, CHN1, HOXA1) and a high-resolution array comparative genomic hybridization (arrayCGH) was performed in two unrelated children with sporadic CFEOM1.

Results

Two unrelated Saudi patients did not have any mutation(s) after sequencing the full coding regions of SALL4, CHN1, HOXA1, and TUBB3 genes; and exons 8, 20, and 21 of the KIF21A gene. However, arrayCGH revealed a 3.17 Kb deletion at chromosome 8p22 with copy number state equal to 1, indicating a heterozygous deletion. This deletion was absent in proband’s mother or father or 220 unrelated healthy individuals of similar ethnicity. The deletion encompassed only one functional gene, GRHL2, which encodes a transcription factor. In humans, defects in this gene are a cause of non-syndromic sensorineural deafness, autosomal dominant type 28 (DFNA28). We speculate that GRHL2 gene may have a role in orbital innervations and the defect in this gene (deletion) may be related to the CFEOM1 phenotype in these two children.

The genetics of nonsyndromic bilateral Duane retraction syndrome

PURPOSE

To assess the importance of monogenic mutations and chromosomal copy number variants (CNVs) in the occurrence of nonsyndromic bilateral Duane retraction syndrome (bilateral nsDRS).

METHODS

The medical records of 12 patients with bilateral nsDRS were reviewed. Genes associated with DRS and associated congenital cranial dysinnervation disorders (SALL4, CHN1, HOXA1, TUBB3, and KIF21A) were sequenced in the standard fashion in each patient. Array comparative genomic hybridization (array CGH) was performed using Affymetrix Cytogenetics Whole-Genome 2.7M array, and the results were analyzed using Affymetrix Chromosome Analysis Suite v1.2. CNVs were assessed as unlikely to be pathologic if they were also present in the Database of Genomic Variants (DGV) or our local database of array CGH results in 150 normal individuals of Middle Eastern ethnicity.

RESULTS

No patient had a sequence mutation in SALL4, CHN1, HOXA1, TUBB3, or KIF21A. These 12 patients each had 36-42 chromosomal deletions and/or duplications (mean with standard deviation, 26.25 ± 6.77), but all of these CNVs were present either in the DGV or in our local database of normal individuals of similar ethnicity and, therefore, are considered nonpathogenic.

CONCLUSIONS

The results reported here suggest that bilateral nsDRS is not usually associated with mutations in these genes or with chromosomal CNVs. Current evidence suggests other factors such as epigenetic and/or teratogenic abnormalities may be a potential cause of bilateral nsDRS.

Multiple Ocular and Systemic Disorders in Association with Bilateral Duane's Retraction Syndrome

Duane's retraction syndrome (DRS) is characterized by limitations in horizontal eye movements, globe retraction, and palpebral fissure narrowing on attempted adduction. This disorder is caused by a disturbance in innervation originating in the brain stem and represents <1% of all cases of strabismus. It is postulated that this syndrome is due to an insult during the early weeks (8-10 weeks) of pregnancy and is 10-20 times more frequently associated with other systemic congenital anomalies. This case report of bilateral DRS included bilateral iris-retinal coloboma and congenital heart disease, sensory hearing loss, and inguinal hernia.

Duane retraction syndrome in a patient with Duchenne muscular dystrophy

PURPOSE

We describe the clinical features of a boy with bilateral Duane retraction syndrome (DRS), Duchenne muscular dystrophy (DMD), and other medical problems.

METHODS

The child was followed-up for five years; his chart was reviewed, including the results of a muscle biopsy and genetic testing. Multiplex ligation-dependent probe amplification (MLPA) was used to interrogate deletions/duplications in the dystrophin gene.

RESULTS

The proband had bilateral DRS with otherwise normal ocular motility; he also had developmental delay, mild mental retardation, and seizures. Clinical diagnosis of DMD included progressive proximal weakness, highly elevated creatine kinase levels, and a muscle biopsy showing significant dystrophic changes including contracted, degenerative, and regenerative fibers, and negative dystrophin immunostaining. MLPA documented duplication of exons 3 and 4 of the dystrophin gene.

CONCLUSIONS

This boy is the third patient to be reported with DRS and DMD, the second with bilateral DRS and the only one with other neurologic features. Mutated dystrophin is present in extraocular muscles and in the central nervous system (CNS) in DMD, leaving open the question of whether this co-occurrence is the result of the genetic muscle abnormality, CNS effects caused by dystrophin mutations, or chance.

Modified Y-splitting Procedure for the Treatment of Duane Retraction Syndrome

OBJECTIVES

To present the outcomes of modified lateral rectus Y-splitting combined with either unilateral or bilateral horizontal rectus recession in Duane Retraction Syndrome (DRS) with significant upshoot or downshoot.

MA­TE­RI­ALS AND MET­HODS

A total of 12 patients including 10 patients with Type I DRS and 2 with Type III DRS underwent modified Y-splitting surgery. Amount of additional recessions varied with the degree of preoperative deviation by intraoperative adjustable suture technique. Preoperatively 3 patients had esotropia (ET), 6 had exotropia (XT), and 3 patients had orthotropia. The mean preoperative deviation was 19.3 prism diopters (PD) (range, 18-20 PD) in ET patients and 19.2 PD (range, 16-20 PD) in XT patients.

RE­SULTS

Postoperatively, all patients had significant correction in horizontal deviation and aligned within 4 PD of orthotropia, and no patients exhibited abnormal head posture. Co-contraction and globe retraction were markedly reduced and abnormal ocular vertical movement disappeared or significantly decreased in all cases. No patients experienced recurrence of ocular motility disorders in the mean 26-month (range, 13-66 months) follow-up period.

CONCLUSION

Modified Y-splitting surgery combined with co-contracting horizontal muscle recession technique seems to be a safe and effective treatment in DRS.

The congenital cranial dysinnervation disorders

Congenital cranial dysinnervation disorders (CCDD) encompass a number of related conditions and includes Duane syndrome, congenital fibrosis of the external ocular muscles, Möbius syndrome, congenital ptosis and hereditary congenital facial paresis. These are congenital disorders where the primary findings are non-progressive and are caused by developmental abnormalities of cranial nerves/nuclei with primary or secondary dysinnervation. Several CCDD genes have been found, which enhance our understanding of the mechanisms involved in brain stem development and axonal guidance.

Cervico-Oculo-Acoustic Syndrome in a Male with Consanguineous Parents

Background:

The cervico-oculo-acoustic syndrome comprises Klippel-Feil anomaly, sensorineural deafness and Duane's retraction syndrome. Polygenic, autosomal dominant, and X-linked inheritance have been hypothesized. The disorder has rarely been reported in males.

Case Report:

A 42-year-old male, born of consanguineous parents, presented with Duane's syndrome, mixed hearing loss, C2-C3 fusion, neck stiffness, and right facial palsy. A variety of cardiac, neurological and urogenital anomalies occurred in his relatives. The electro-oculographic studies showed impaired abduction and adduction of the right eye and impaired abduction of the left eye. Vergence, vertical eye movements and peripheral vestibular responses were normal. Somatosensory evoked potentials showed absence of the N13 peak and brainstem auditory evoked potentials bilateral delay of the I-III interpeak latencies.

Conclusions:

Consanguinity of the patient's parents, not previously reported, suggests autosomal recessive inheritance, but autosomal dominant inheritance is indicated by the family history. The pattern of the oculomotor deficit is consistent with bilateral dysplasia of the abducens nuclei with preserved internuclear neurons in the right abducens nucleus. Neurophysiological investigations revealed lower brainstem and cervical cord involvement.

Strabismus genetics across a spectrum of eye misalignment disorders

Eye misalignment, called strabismus, is amongst the most common phenotypes observed, occurring in up to 5% of individuals in a studied population. While misalignment is frequently observed in rare complex syndromes, the majority of strabismus cases are non-syndromic. Over the past decade, genes and pathways associated with syndromic forms of strabismus have emerged, but the genes contributing to non-syndromic strabismus remain elusive. Genetic testing for strabismus risk may allow for earlier diagnosis and treatment, as well as decreased frequency of surgery. We review human and model organism literature describing non-syndromic strabismus, including family, twin, linkage, and gene expression studies. Recent advances in the genetics of Duane retraction syndrome are considered, as relatives of those impacted show elevated familial rates of non-syndromic strabismus. As whole genome sequencing efforts are advancing for the discovery of the elusive strabismus genes, this overview is intended to support the interpretation of the new findings.

CCDD Phenotype Associated with a Small Chromosome 2 Deletion

PURPOSE

Some individuals are born with congenital limitation of ocular motility, often associated with ptosis and retraction of the globe. Many of these disorders are now known as the congenital cranial dysinnervation disorders (CCDDs). While several genes have been associated with CCDD phenotypes, there are still patients for whom the genetic basis has not been identified.

METHODS

Clinical evaluation and neuroimaging, sequencing of candidate genes, and array comparative genomic hybridization (array CGH).

RESULTS

The patient was a four-year-old girl with mild dysmorphism; bilateral mild ptosis; substantial limitation of abduction OS with milder limitations of abduction OD, adduction OS, and vertical gaze OS; and retraction OS > OD on attempted adduction. No mutations were detected in the HOXA1, KIF21A, SALL4, TUBB3, and CHN1 genes. Array CGH revealed a 8 Kb de novo deletion on chromosome 2 (2q24.3) that encompassed a portion of only one gene, the Xin Actin-binding Repeat containing 2 (Gene Symbol XIRP2; NM_001079810). This gene encodes a protein that is involved in muscle development and protecting actin filaments from depolymerization. It interacts functionally with 10 other proteins playing a similar role in muscle development.

CONCLUSIONS

This patient's chromosomal abnormality affected only one gene that currently seems involved only in muscle development. All other genes currently associated with the CCDDs affect neurologic development. Genetic information from this patient implies that genes involved in development and maintenance of extraocular muscles can cause congenital ocular motility disorders as well.

Narcolepsy Associated with Duane's Syndrome

The best characterised disorder of REM sleep, narcolepsy has never previously been associated with Duane’s syndrome, in which there is developmental failure of the abducens nerve and its nucleus. The major brain stem nuclei responsible for REM sleep generation are situated in the pons in close proximity to the abducens nerve nucleus. We report the novel combination of Duane’s syndrome and narcolepsy, providing new insight into the pathogenesis of narcolepsy.

Duplicate internal auditory canals with facial and vestibulocochlear nerve dysfunction

Objective:

We report an extremely rare case of duplication of the internal auditory canal associated with dysfunction of both the facial and vestibulocochlear nerves. We also review the literature regarding the integrity of the facial and vestibulocochlear nerves in such cases.

Case report:

A 34-year-old man presented with unilateral, right-sided, sensorineural hearing loss and facial nerve palsy since childhood. Facial nerve function was observed to be House–Brackmann grade III. Computed tomography and magnetic resonance imaging demonstrated ipsilateral duplicate, vacant internal auditory canals. Based on the clinical presentation, we interpreted these radiological findings as aplasia of the vestibulocochlear nerve and severe hypoplasia of the facial nerve.

Conclusion:

To our best knowledge, this is the first report of vestibulocochlear nerve aplasia and severe facial nerve hypoplasia in a case of ipsilateral duplication of the internal auditory canal. High resolution gradient echo magnetic resonance imaging sequences are advocated for assessment of neural integrity in patients with an abnormal internal auditory canal and facial and/or vestibulocochlear nerve dysfunction.

Carboxypeptidase A6 in zebrafish development and implications for VIth cranial nerve pathfinding

Carboxypeptidase A6 (CPA6) is an extracellular protease that cleaves carboxy-terminal hydrophobic amino acids and has been implicated in the defective innervation of the lateral rectus muscle by the VIth cranial nerve in Duane syndrome. In order to investigate the role of CPA6 in development, in particular its potential role in axon guidance, the zebrafish ortholog was identified and cloned. Zebrafish CPA6 was secreted and interacted with the extracellular matrix where it had a neutral pH optimum and specificity for C-terminal hydrophobic amino acids. Transient mRNA expression was found in newly formed somites, pectoral fin buds, the stomodeum and a conspicuous condensation posterior to the eye. Markers showed this tissue was not myogenic in nature. Rather, the CPA6 localization overlapped with a chondrogenic site which subsequently forms the walls of a myodome surrounding the lateral rectus muscle. No other zebrafish CPA gene exhibited a similar expression profile. Morpholino-mediated knockdown of CPA6 combined with retrograde labeling and horizontal eye movement analyses demonstrated that deficiency of CPA6 alone did not affect either VIth nerve development or function in the zebrafish. We suggest that mutations in other genes and/or enhancer elements, together with defective CPA6 expression, may be required for altered VIth nerve pathfinding. If mutations in CPA6 contribute to Duane syndrome, our results also suggest that Duane syndrome can be a chondrogenic rather than a myogenic or neurogenic developmental disorder.

Substrate specificity of human carboxypeptidase A6

Carboxypeptidase A6 (CPA6) is an extracellular matrix-bound metallocarboxypeptidase (CP) that has been implicated in Duane syndrome, a neurodevelopmental disorder in which the lateral rectus extraocular muscle is not properly innervated. Consistent with a role in Duane syndrome, CPA6 is expressed in a number of chondrocytic and nervous tissues during embryogenesis. To better characterize the enzymatic function and specificity of CPA6 and to compare this with other CPs, CPA6 was expressed in HEK293 cells and purified. Kinetic parameters were determined using a panel of synthetic carboxypeptidase substrates, indicating a preference of CPA6 for large hydrophobic C-terminal amino acids and only very weak activity toward small amino acids and histidine. A quantitative peptidomics approach using a mixture of peptides representative of the neuropeptidome allowed the characterization of CPA6 preferences at the P1 substrate position and suggested that small and acidic P1 residues significantly inhibit CPA6 cleavage. Finally, a comparison of available kinetic data for CPA enzymes shows a gradient of specificity across the subfamily, from the very restricted specificity of CPA2 to the very broad activity of CPA4. Structural data and modeling for all CPA/B subfamily members suggests the structural basis for the unique specificities observed for each member of the CPA/B subfamily of metallocarboxypeptidases.

Detailed magnetic resonance imaging findings of the ocular motor nerves in Duane's retraction syndrome

PURPOSE

To study the neuroanatomic characteristics of patients with Duane's retraction syndrome with high-resolution magnetic resonance imaging.

METHODS

The study included 11 consecutive cases, including five patients with type I, one patient with type II, four patients with type III, and one patient with inverse Duane's retraction syndrome. The patients underwent magnetic resonance imaging of the brain, brain stem, cavernous sinus, and orbits.

RESULTS

In 10 patients, the abducens nerve (cranial nerve VI) was absent or showed hypoplasia in the brain stem, cavernous sinus, and orbit. However, these findings were not seen in the patient who had inverse Duane's retraction syndrome. In two children, magnetic resonance imaging showed that the cavernous sinuses were smaller on the affected side. The inferior division of the oculomotor nerve (cranial nerve III) was traced to enter the lateral rectus muscle or had intimate continuity with the lateral rectus muscle in nine patients with type I and type III Duane's retraction syndrome. In one patient with type III Duane's retraction syndrome, the oculomotor foramen was significantly larger on the affected side than on the sound side. In the patient with type II Duane's retraction syndrome, the superior division of cranial nerve III was enlarged and had three branches. In the patient with inverse Duane's retraction syndrome, the inferior division of cranial nerve III sent two branches to the medial rectus muscle, and the patient had superior oblique muscle hypoplasia.

CONCLUSION

Neuroimaging findings showed that the absence of cranial nerve VI, hypoplasia in the brain stem, and an extra branch of the inferior division of cranial nerve III to the lateral rectus muscle is the most common presentation of Duane's retraction syndrome, but not the only one. The aberrant branches likely correspond to the abnormal eye movement seen in patients with this disorder.

Left-sided Duane's Syndrome and Retinal Coloboma associated with Contralateral Microphthalmia

Case report of a 15-year-old girl presenting with a left-sided Duane's retraction syndrome (DURS) in combination with ipsilateral retinal coloboma and contralateral microphthalmia. Abduction limitation as well as narrowing of the palpebral fissure and globe retraction during attempted adduction (type I DURS) was demonstrated in the left eye. Additionally, a retinal coloboma was observed in the nasal inferior quadrant of the left eye. No other somatic or developmental abnormalities were observed and karyotypic analysis was normal. This is the first case of non-syndromic unilateral DURS associated with a contralateral major ocular malformation. This unusual clinical combination probably arose from the embryonic action of an eye-specific disruptor.

Synergistic divergence: a distinct ocular motility dysinnervation pattern

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 ophthalmic 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

The patients did not meet the clinical criteria for CFEOM types 1, 2, or 3. Each patient had severe adduction weakness on the affected side and 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 may be 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.

Midline orofacial cleft defects in association with type 1 Duane's retraction syndrome

Anomalies of ocular motility associated with Duane's retraction syndrome (DRS) have often been perceived as isolated phenomena arising as a result of congenital ocular miswiring between the lateral and medial recti muscles. Interestingly, the reporting of concomitant ocular and systemic anomalies arising in the setting of DRS discounts this narrow perception and highlights the importance of a thorough investigation for non-ocular comorbidities. A 37-year-old Caucasian male presented for a routine ocular examination with complaints of gradual reduction in uncorrected near vision. Our testing confirmed the characteristic deficit of abduction, palpebral fissure narrowing and globe retraction consistent with a type 1 Duane's defect of the right eye. A midline cleft lip and palate were also noted in the absence of signs of nuchal rigidity/reduced range of motion in the cervical spine, spinal misalignment, deafness, optic nerve anomalies, hypertelorism or altered mental state. Awareness of key comorbidities and the importance of thorough clinical evaluation with appropriate supplemental testing and consultation with a paediatric ophthalmologist are warranted in non-isolated presentations of DRS.

Characterization of carboxypeptidase A6, an extracellular matrix peptidase

Carboxypeptidase A6 (CPA6) is a member of the M14 metallocarboxypeptidase family that is highly expressed in the adult mouse olfactory bulb and broadly expressed in embryonic brain and other tissues. A disruption in the human CPA6 gene is linked to Duane syndrome, a defect in the abducens nerve/lateral rectus muscle connection. In this study the cellular distribution, processing, and substrate specificity of human CPA6 were investigated. The 50-kDa pro-CPA6 is routed through the constitutive secretory pathway, processed by furin or a furin-like enzyme into the 37-kDa active form, and secreted into the extracellular matrix. CPA6 cleaves the C-terminal residue from a range of substrates, including small synthetic substrates, larger peptides, and proteins. CPA6 has a preference for large hydrophobic C-terminal amino acids as well as histidine. Peptides with a penultimate glycine or proline are very poorly cleaved. Several neuropeptides were found to be processed by CPA6, including Met- and Leu-enkephalin, angiotensin I, and neurotensin. Whereas CPA6 converts enkephalin and neurotensin into forms known to be inactive toward their receptors, CPA6 converts inactive angiotensin I into the biologically active angiotensin II. Taken together, these data suggest a role for CPA6 in the regulation of neuropeptides in the extracellular environment within the olfactory bulb and other parts of the brain.

Duane's retraction syndrome, a case series from Iran

PURPOSE

To determine the relative prevalence of Duane's retraction syndrome (DRS) in a population of Iranian strabismus cases and to describe the clinical features.

METHODS

Retrospectively, a population of 7,349 strabismus cases visited during 2000-2003 were evaluated for the diagnosis of DRS. Data regarding onset (noticed age), type, head turn, primary position deviation, narrowing of the palpebral fissure, leash phenomenon, refractive error, amblyopia, and history of surgery were collected. Chi-square test and Student's t-test were used.

RESULTS

About 125 DRS cases were diagnosed (prevalence: 1.7%). The noticed age of the syndrome was at birth in 35.6%, during infancy in 25.4%, or childhood in 39.0%; the age at referral ranged from 3.5 months to 65.0 (median: 10.0) years. The female/male and left/right eye involvement ratios were 3:2 and 3.5:1, respectively. The syndrome was of type I in 87.0%, II in 6.5%, and III in 5.7%; 7.2% were bilateral. Horizontal deviations existed in 76.0% and vertical deviations in 12.8%. 26.8% had different degrees of amblyopia. Leash phenomenon was detected in 37.6% of cases. Head turn, primary position deviation (without turn), and orthophoria were observed in 71.2%, 13.6%, and 15.2%. Surgery had been performed in 71.2% of the cases. Vertical deviations and leash phenomenon were more common in types II and III and hypermetropia in type I (P values: 0.036, <0.001, and 0.025, respectively).

CONCLUSION

Basic features of our series seem to be comparable with previous reports. The incidences of bilateral involvement and type III syndrome were lower. The proportion of cases with head turn was higher and surgery was performed more frequently.

Interstitial deletion of 1q42.13-q43 with Duane retraction syndrome

Duane retraction syndrome is a congenital eye movement disorder characterized by failure of the sixth cranial nerve or nucleus to develop properly, resulting in restriction of abduction, narrowing of the palpebral fissure, and retraction of the globe on attempted adduction and/or restricted adduction. The gene loci of Duane syndrome have been mapped on 8q and 2q, indicating a heterogeneity. We report here a patient with interstitial deletion of 1q with Duane syndrome. The karyotype of our patient suggests another possible locus of the Duane syndrome, and the mapped genes around the deleted region, 1q42.13-43, contain possible candidate genes such as a homeobox gene. However, further clinical descriptions of patients with Duane syndrome and genetic investigations of the deleted regions are needed for a more accurate delineation.

Clinical characteristics of bilateral Duane syndrome

PURPOSE

To describe the clinical characteristics of bilateral Duane syndrome.

METHODS

Retrospective medical record review (1982 to 2003) for patients with a diagnosis of Duane syndrome (examined by a pediatric ophthalmologist) who were bilaterally affected and had no prior ocular surgery. Data collected included type of Duane syndrome, gender, family history for strabismus, abnormal head position, versions, strabismus measurements, associated ocular and/or nonocular abnormalities, and amblyopia status.

RESULTS

Of 270 patients with the diagnosis of Duane syndrome, 37 (14%) were bilaterally affected. None had ocular surgery prior to referral. Twenty-two (59%) were male, 35 (95%) had the same Duane syndrome type in both eyes, 29 (78%) had strabismus in primary position, 9 (24%) had ocular and nonocular congenital abnormalities, 6 (16%) had amblyopia, and 8 (22%) had a recorded strabismus family history.

CONCLUSIONS

Unlike unilateral Duane syndrome, bilateral Duane syndrome may be more common in males and associated with a higher prevalence of strabismus in primary gaze position. The prevalences of amblyopia, positive strabismus family history, and associated congenital abnormalities in this series of bilateral cases is similar to the reported prevalence.

Isolated atlantal stenosis in a patient with idiopathic growth hormone deficiency, and Klippel-Feil and Duane's syndromes

OBJECTIVE AND IMPORTANCE

Isolated atlantal stenosis is very rare with less than ten cases reported, mostly in adult Asians; however, this pathology should be recognized by the neurosurgeon. An unusual case of this rare clinical entity is reported in conjunction with multiple other anomalies.

CLINICAL PRESENTATION

We report a Caucasian girl with symptomatic stenosis of the first cervical vertebrae who presented with episodes of loss of tone with subsequent falling, facial cyanosis, urinary incontinence, hand weakness, and difficulties with swallowing. This patient also had the diagnoses of Duane's and Klippel-Feil syndromes, and idiopathic growth hormone deficiency. In addition, this patient was found to have retroflexion of the odontoid process, which further compromised the spinal canal. Flexion-extension radiographs failed to identify cervical spine instability.

INTERVENTION

Following suboccipital craniectomy and the removal of the posterior arch of the atlas, the patient's symptoms were resolved and her urinary incontinence improved.

CONCLUSIONS

We theorize that our case represents a variant of Wildervanck syndrome. Further case reports are necessary to verify that isolated atlantal stenosis is a component of this constellation of findings. Furthermore, our case demonstrates that degenerative changes of the spine are not necessary for the production of symptoms in cases of isolated stenosis of the atlas.

A report of three patients with an interstitial deletion of chromosome 15q24

Partial monosomy of the q2 region of chromosome 15 has been infrequently reported. Moreover, interstitial deletions involving 15q22-q24 have been described in only nine patients to date. The phenotype of these reported individuals is subject to the extent of the deletion but typically includes altered muscle tone and significant developmental delays. In addition, eye abnormalities, such as strabismus, microphthalmia, or colobomas, ear abnormalities including cleft earlobe and preauricular tags, and urogenital defects are common features. Congenital heart defects, diaphragmatic hernia, abnormalities of the central nervous system, and skeletal anomalies have been reported but appear to be less frequent clinical manifestations. In this report, we describe three new patients with interstitial deletions involving 15q24, two with cryptic deletions identified by fluorescence in situ hybridization (FISH) with a probe for the PML gene and one with a cytogenetically visible deletion of 15q22.3-q24. The clinical presentation of these individuals is similar to those previously described and includes global developmental delays, hypotonia, and genital abnormalities in the males. The identification of these three cases demonstrates that the above clinical features are associated with a new cytogenetic deletion syndrome. Furthermore, we suggest that FISH analysis with a probe for the PML gene be performed in patients with these physical findings.

Familial ptotic lid elevation during ipsilateral abduction

PURPOSE

To report and discuss the clinical findings of a 17-member family with 2 siblings who exhibit ptosis and abnormal synkinetic lid elevation associated with ipsilateral abduction.

SUBJECTS AND METHODS

Sixteen members of the 17-member immediate family underwent ophthalmic examination.

RESULTS

Two siblings exhibited ptosis and abnormal synkinetic lid elevation associated with ipsilateral abduction. One was bilaterally affected and the other had unilateral findings. A third sibling had isolated bilateral congenital ptosis. A fourth demonstrated classic Duane syndrome Type I in the right eye. Other family members did not have ophthalmic abnormalities.

CONCLUSIONS

A unifying mechanism of congenital cranial dysinnervation may underlie these and similar phenotypes of oculomotor and/or abducens nerve abnormalities with or without abnormal synkinesis.

Normal and aberrant craniofacial myogenesis by grafted trunk somitic and segmental plate mesoderm

Our research assesses the ability of three trunk mesodermal populations– medial and lateral halves of newly formed somites, and presomitic(segmental plate) mesenchyme – to participate in the differentiation and morphogenesis of craniofacial muscles. Grafts from quail donor embryos were placed in mesodermal pockets adjacent to the midbrain-hindbrain boundary,prior to the onset of neural crest migration, in chick host embryos. This encompasses the site where the lateral rectus and the proximal first branchial arch muscle primordia arise. The distribution and differentiation of graft-derived cells were assayed using QCPN and QH1 antibodies to identify all quail cells and quail endothelial cells, respectively. Chimeric embryos were assayed for expression of myf5, myod, paraxis and lbx1, and the synthesis of myosin heavy chain (MyHC), between 1 and 6 days later (stages 14-30). Heterotopic and control (orthotopic) transplants consistently produced invasive angioblasts, and contributed to the lateral rectus and proximal first branchial arch muscles; many also contributed to the dorsal oblique muscle. The spatiotemporal patterns of transcription factor and MyHC expression by these trunk cells mimicked those of normal head muscles. Heterotopic grafts also gave rise to many ectopic muscles. These were observed in somite-like condensations at the implant site, in dense mesenchymal aggregates adjacent to the midbrain-hindbrain boundary, and in numerous small condensations scattered deep to the dorsal margin of the eye. Cells in ectopic condensations expressed trunk transcription factors and differentiated rapidly, mimicking the trunk myogenic timetable. A novel discovery was the formation by grafted trunk mesoderm of many mononucleated myocytes and irregularly oriented myotubes deep to the eye. These results establish that the head environment is able to support the progressive differentiation of several distinct trunk myogenic progenitor populations, over-riding whatever biases were present at the time of grafting. The spatial and temporal control of head muscle differentiation and morphogenesis are very site specific, and head mesoderm outside of these sites is normally refractory to, or inhibited by, the signals that initiate ectopic myogenesis by grafted trunk mesoderm cells.

Duane's syndrome and giant parietal foramina

We report a 14-month-old male with Duane's syndrome and bilateral parietal calvarial defects. This child had no other known medical conditions. The Duane's syndrome involved the left eye. Imaging was demonstrative of bilateral enlarged parietal foramina. We believe this to be the first reported case of simultaneous Duane's syndrome and bilateral giant parietal foramina. Further case reports of our current association are required to determine if these simultaneous findings are spurious or a low-frequency association.

Development of oculomotor axon projections in the chick embryo

The pattern of innervation of the extraocular muscles is highly conserved across higher vertebrate species and mediates sophisticated visuomotor processes. Defects in oculomotor development often lead to strabismus, a misalignment of the eyes that can cause partial blindness. Although it has been intensively studied from a clinical perspective, relatively little is known about how the system develops embryonically. We have therefore mapped the development of the oculomotor nerve (OMN) in chick embryos by using confocal microscopy. We show that OMN development follows a series of stereotyped steps that are tightly regulated in space and time. The OMN initially grows past three of its targets to innervate its distal target, the ventral oblique muscle, only later forming branches to the more proximal muscles. We have also investigated spatiotemporal aspects of the unusual contralateral migration of a subpopulation of oculomotor neurons by using molecular markers and have found the semaphorin axon guidance molecules and their receptors, the neuropilins, to be expressed in discrete subnuclei during this migration. Finally, we have created an embryological model of Duane retraction syndrome (DRS), a form of strabismus in which the OMN is believed to innervate aberrantly the lateral rectus, the normal target of the abducens nerve. By ablating rhombomeres 5 and 6 and hence the abducens, we have mimicked a proposed oculomotor deficit occurring in DRS. We find that the absence of the abducens nerve is not sufficient to produce this inappropriate innervation, so other factors are required to explain DRS.