Ocular and oculomotor signs in Joubert syndrome

Age-Related Neurodevelopmental Features in Children with Joubert Syndrome

Joubert syndrome (JS) is a rare inherited disorder of central nervous system with neonatal/infantile onset, mainly affecting cerebellum and brainstem, and clinically characterized by agenesis or dysgenesis of the cerebellar vermis with accompanying brainstem malformations. More than 20 disease-causing genes have been associated with JS but a clear genotype–phenotype correlation has not been assessed yet. Diagnosis is usually confirmed by detection of the JS neuroradiological hallmark, the molar tooth sign. Patients with JS typically present with neurological manifestations, moreover, a heterogeneous spectrum of multisystemic anomalies may be observed. Signs and symptoms onset varies according to the age range and clinical diagnosis might become complicated. Moreover, specific neurodevelopmental disorders can be associated with JS such as autism spectrum disorders, attention deficit with hyperactivity, and a wide range of behavioral disturbances. Here, we examined the main neurological and neurodevelopmental features of JS according to an age-dependent mode of presentation. Furthermore, differential diagnosis with other neurological syndromes was closely reviewed.

A new gene mutation in a family with idiopathic infantile nystagmus

Idiopathic infantile nystagmus (IIN) is an inherited disease, which can occur through a number of different inheritance patterns (autosomal dominant, recessive, or X-linked). The most common of these is X-linked inheritance with incomplete penetrance and variable expressivity, and can also be dominant or recessive. To date, only two mutations have been described: the first, affecting the FPR143 gene, which is associated with ocular albinism type I, and located on chromosome Xp22, and the second, affecting the FRMD7 gene located on chromosome X26-q27. To date, a causative gene on locus Xp11.3p11.4 has not yet been identified. The most common cause of IIN is due to mutations in the FRMD7 gene, located on chromosome Xq26. We present a case of a new mutation found in three siblings from a family with FRMD7-related infantile nystagmus, whose parents are consanguineously related in the first degree. A complex mutation has occurred in this family, which, to date, has not been previously reported in the scientific literature. The complex mutation consists of the presence of three consecutive 1 bp deletions in exon 12 (c.1248delT; 1299del C; and 1312delT), causing a secondary deletion (c. 1340–2145 + 214del), and resulting in a truncated protein. We also present a 7-year-old patient from a different family, with periodic alternating nystagmus, having no mutation in the FRMD7 gene, which we assume may be an example of non-FRMD7-related IIN. This patient does not have a family history of nystagmus.

A Focus on the Cerebellum: From Embryogenesis to an Age-Related Clinical Perspective

The cerebellum and its functional multiplicity and heterogeneity have been objects of curiosity and interest since ancient times, giving rise to the urge to reveal its complexity. Since the first hypothesis of cerebellar mere role in motor tuning and coordination, much more has been continuously discovered about the cerebellum’s circuitry and functioning throughout centuries, leading to the currently accepted knowledge of its prominent involvement in cognitive, social, and behavioral areas. Particularly in childhood, the cerebellum may subserve several age-dependent functions, which might be compromised in several Central Nervous System pathologies. Overall, cerebellar damage may produce numerous signs and symptoms and determine a wide variety of neuropsychiatric impairments already during the evolutive age. Therefore, an early assessment in children would be desirable to address a prompt diagnosis and a proper intervention since the first months of life. Here we provide an overview of the cerebellum, retracing its morphology, histogenesis, and physiological functions, and finally outlining its involvement in typical and atypical development and the age-dependent patterns of cerebellar dysfunctions.

Visual Evoked Potentials in Joubert Syndrome: A Suggested Useful Method for Evaluating Future Approaches Targeted to Improve Visual Pathways' Function

Introduction

Joubert syndrome (JS) is a recessive disorder characterized by a congenital malformation of the mid-hindbrain and a large spectrum of clinical features including optic nerve morphologic abnormalities. The function of the visual pathways, including the optic nerve, can be objectively evaluated by visual evoked potential (VEP) recordings. Our work aims to employ VEP to evaluate the neural conduction along the visual pathways in JS patients with or without optic nerve morphologic abnormalities (ONMA).

Methods

In this observational and prospective study, 18 children with genetic diagnosis of JS (mean age 8.78 ± 5.87 years) and 17 healthy age-similar control subjects (control group, 9.05 ± 6.02 years) were enrolled.

Based on presence/absence of ONMA at fundus examination, JS patients were divided into two groups: the JS-A group (eight patients with ONMA) and JS-N group (ten patients without ONMA). Following the ISCEV standards, pattern VEPs were recorded in patients and controls in response to 60’ and 15’ checks to obtain a prevalent activation of large or small axons, respectively.

Results

Compared to controls, both the JS-A and JS-N groups showed significant abnormalities in 60’ and 15’ VEP implicit time and amplitude. Only in the JS-N group were values of 15’ VEP implicit significantly correlated with the corresponding values of visual acuity.

Conclusions

Our results suggest that a visual pathways dysfunction (of both large and small axons) detectable by VEP may occur in JS patients regardless of the presence of ONMA. Since clinical trials are envisaged in the near future to address JS-related ocular problems, our results might provide information about the potential usefulness of VEP recordings to assess the efficacy of treatments targeted to improve the visual pathways’ function.

Electroretinographic Assessment in Joubert Syndrome: A Suggested Objective Method to Evaluate the Effectiveness of Future Targeted Treatment

INTRODUCTION

Joubert syndrome (JS) is an autosomal recessive disorder characterized by a congenital malformation of the mid-hindbrain and a large spectrum of clinical features including congenital retinal dystrophy. The function of different retinal elements (rod, cone, bipolar cells) can be objectively evaluated by electroretinogram (ERG) recordings. Our work aims to evaluate the retinal function (by ERG recordings) in patients with JS with or without congenital retinal dystrophy. In addition, since clinical trials should be performed in the near future in JS, our results could provide information about the possible usefulness of ERG recordings in the assessment of the efficacy of treatments targeted to improve the retinal involvement.

METHODS

In this observational and prospective study, 24 children with genetic identification for JS (mean age 10.75 ± 6.59 years) and 25 healthy age-similar normal control subjects (control group, mean age 10.55 ± 3.76 years) were enrolled. On the basis of the presence/absence of retinal dystrophy at fundus examination, patients with JS were divided into two groups: patients with JS with retinal dystrophy (16 children, mean age 11.00 ± 6.74 years, providing 16 eyes; JS-RD group) and patients with JS without retinal dystrophy (8 children, mean age 10.50 ± 6.45 years, providing 8 eyes; JS-NRD group). In patients with JS and controls, visual acuity (VA), dark-adapted, light-adapted, and 30-Hz flicker ERGs were performed according to International Society for Clinical Electrophysiology of Vision (ISCEV) standard protocols.

RESULTS

When compared to controls, patients in the JS-RD and JS-NRD groups showed significant abnormalities of the values of dark-adapted, light-adapted, and 30-Hz flicker ERG parameters. The ERG and VA changes were not significantly correlated.

CONCLUSIONS

Our results suggest that a dysfunction of photoreceptors and bipolar cells occurs in patients with JS with or without retinal dystrophy. The retinal impairment can be detected by ERG recordings and this method should be proposed to evaluate the effectiveness of adequate treatment targeted to improve the retinal impairment in patients with JS.

Bilateral Morning Glory Syndrome with Bilateral Persistent Fetal Vasculature in a Patient with Joubert's Syndrome

Purpose. We report a case of a 1-year-old girl who was referred to us with a cerebellar anomaly and delayed growth and development for bilateral ptosis and poor fixation. Based on our ophthalmologic examination, we concluded that she has bilateral persistent fetal vasculature (PFV) with morning glory syndrome (MGS). A closer look into her neurologic condition revealed that she has Joubert's syndrome. Observations. External examination revealed bilateral symmetrical ptosis with syndromic facies and her fundus examination revealed a large dysplastic optic disc with anomalous radiating vessels and a fibrous tissue tuft originating from the disc. The left eye showed similar findings in addition to a central excavation and a fibrovascular stalk extending from the optic disc. These findings were consistent with bilateral MGS and bilateral PFV. The brain imaging included a computed tomography scan and magnetic resonance imaging, both of which revealed a "molar tooth appearance" of the midbrain and an anomalous cerebellum suggestive of Joubert's syndrome. Conclusions and Importance. This is the first case report of a case of bilateral MGS and bilateral PFV associated with Joubert's syndrome. This case report documents the associated optic nerve disease in these patients, not previously described, which are additive causes of visual compromise in addition to the brain insult.

Ocular Motor System Control Models and the Cerebellum: Hypothetical Mechanisms

To review our studies and "top-down" models of saccadic intrusions and infantile nystagmus syndrome with the aim of hypothesizing areas of cerebellar connections controlling parts of the ocular motor subsystems involved in both types of function and dysfunction. The methods of eye-movement recording and modeling are described in detail in the cited references. Saccadic intrusions, such as square-wave jerks and square-wave oscillations, can be simulated by a single malfunction, whereas staircase saccadic intrusions required two independent malfunctions. The major infantile nystagmus syndrome waveforms are traceable to a failure to calibrate the damping ratio of the smooth pursuit system. The use of a behavioral ocular motor system model demonstrated how putative cerebellar dysfunctions could accurately simulate both the oscillations and the ocular motor responses seen in patients with both saccadic and pursuit disorders.

Joubert Syndrome: Ophthalmological Findings in Correlation with Genotype and Hepatorenal Disease in 99 Patients Prospectively Evaluated at a Single Center

PURPOSE

Joubert syndrome (JS) is caused by mutations in >34 genes that encode proteins involved with primary (nonmotile) cilia and the cilium basal body. This study describes the varying ocular phenotypes in JS patients, with correlation to systemic findings and genotype.

DESIGN

Patients were systematically and prospectively examined at the National Institutes of Health (NIH) Clinical Center in the setting of a dedicated natural history clinical trial.

PARTICIPANTS

Ninety-nine patients with JS examined at a single center.

METHODS

All patients underwent genotyping for JS, followed by complete age-appropriate ophthalmic examinations at the NIH Clinical Center, including visual acuity (VA), fixation behavior, lid position, motility assessment, slit-lamp biomicroscopy, dilated fundus examination with an indirect ophthalmoscope, and retinoscopy. Color and fundus autofluorescence imaging, Optos wide-field photography (Dunfermline, Scotland, UK), and electroretinography (ERG) were performed when possible.

MAIN OUTCOME MEASURES

The VA (with longitudinal follow-up where possible), ptosis, extraocular muscle function, retinal and optic nerve status, and retinal function as measured by ERG.

RESULTS

Among patients with JS with quantifiable VA (68/99), values ranged from 0 logarithm of the minimum angle of resolution (logMAR) (Snellen 20/20) to 1.5 logMAR (Snellen 20/632). Strabismus (71/98), nystagmus (66/99), oculomotor apraxia (60/77), ptosis (30/98), coloboma (28/99), retinal degeneration (20/83), and optic nerve atrophy (8/86) were identified.

CONCLUSIONS

We recommend regular monitoring for ophthalmological manifestations of JS beginning soon after birth or diagnosis. We demonstrate delayed visual development and note that the amblyogenic time frame may last significantly longer in JS than is typical. In general, patients with coloboma were less likely to display retinal degeneration, and those with retinal degeneration did not have coloboma. Severe retinal degeneration that is early and aggressive is seen in disease caused by specific genes, such as CEP290- and AHI1-associated JS. Retinal degeneration in INPP5E-, MKS1-, and NPHP1-associated JS was generally milder. Finally, ptosis surgery can be helpful in a subset of patients with JS; decisions as to timing and benefit/risk ratio need to be made on an individual basis according to expert consultation.

Keeping an Eye on Bardet-Biedl Syndrome: A Comprehensive Review of the Role of Bardet-Biedl Syndrome Genes in the Eye

Upwards of 90% of individuals with Bardet-Biedl syndrome (BBS) display rod-cone dystrophy with early macular involvement. BBS is an autosomal recessive, genetically heterogeneous, pleiotropic ciliopathy for which 21 causative genes have been discovered to date. In addition to retinal degeneration, the cardinal features of BBS include obesity, cognitive impairment, renal anomalies, polydactyly, and hypogonadism. Here, we review the genes, proteins, and protein complexes involved in BBS and the BBS model organisms available for the study of retinal degeneration. We include comprehensive lists for all known BBS genes, their known phenotypes, and the model organisms available. We also review the molecular mechanisms believed to lead to retinal degeneration. We provide an overview of the mode of inheritance and describe the relationships between BBS genes and Joubert syndrome, Leber Congenital Amaurosis, Senior-Løken syndrome, and non-syndromic retinitis pigmentosa. Finally, we propose ways that new advances in technology will allow us to better understand the role of different BBS genes in retinal formation and function.

Orocraniofacial findings of a Pediatric Patient with Joubert Syndrome

Joubert syndrome (JS) is a very rare autosomal recessive disorder, involving agenesis or dysgenesis of cerebellar vermis and brain stem. The neurological features of JS include hypotonia, ataxia, developmental delay, intellectual disability, abnormal eye movements, and neonatal breathing dysregulation. These may be associated with multiorgan involvement, mainly retinal dystrophy, nephronophthisis, hepatic fibrosis, and polydactyly. An obligatory hallmark feature associated with JS is the molar tooth sign (MTS), a complex midbrain-hindbrain malformation visible on brain imaging. This case report presents a pediatric case of JS in a 7-year-old girl. Joubert syndrome cases have been reported by various medical specialties in medical journals; however, this probably could be the first report of this rare developmental disorder in dental and oral health.

Infantile-onset saccade initiation delay (congenital ocular motor apraxia)

Infantile-onset saccade initiation delay, also known as congenital ocular motor apraxia, typically presents in early infancy with horizontal head thrusts once head control is achieved. Defective initiation of horizontal saccades and saccade hypometria with normal saccadic velocity are characteristic findings. Isolated impairment of vertical saccades is rare. Impaired smooth ocular pursuit may be seen. Other relatively common features include developmental delay, hypotonia, ataxia, or clumsiness. Brain MRI may be normal or show a diverse range of abnormalities, most commonly involving the cerebellum. Defective slow phases of the optokinetic response are commonly associated with brain MRI abnormalities. Isolated defect of vertical saccade initiation may indicate supratentorial brain abnormalities on MRI. Joubert syndrome, a developmental midbrain-hindbrain malformation, and ataxia telangiectasia are both commonly associated with defective volitional and reflexive saccade initiation, saccade hypometria, and head thrusts. Both horizontal and vertical saccades are impaired in these two disorders.

The syndrome of infantile-onset saccade initiation delay

INTRODUCTION

Infantile-onset saccade initiation delay (ISID), also known as congenital ocular motor apraxia, is characterized by the inability to initiate volitional horizontal saccades. Other abnormalities including developmental delay and ataxia have been reported. The frequency of these abnormalities is unknown. We performed a detailed review of the medical literature to quantify features of ISID.

METHODS

We searched the English medical literature for articles related to ISID from 1952 to 2010. Whenever possible, patients were excluded if they had acquired SID, Joubert syndrome or neurodegenerative conditions. The minimum prevalence was calculated for each abnormality.

RESULTS

Sixty-six articles with information on 288 patients were included in the analysis. Head thrusts were reported in 84.7%. Blinks without head thrusts were used to initiate saccades in 41%. The fast phases of the optokinetic response and vestibulo-ocular reflex were impaired in 69.8% and 34.4% respectively. Smooth ocular pursuit was abnormal in 33%. Global developmental delay occurred in 41.3%, speech or language delay in 36.5%, cognitive delay in 17%, hypotonia in 35.8%, motor delay in 48.6%, and ataxia/clumsiness in 49.3% of patients. Neuroimaging was performed on 197 patients and was normal in 39.1%. Abnormalities involved the cerebellum (24.9%), cerebrum (15.7%), other infratentorial structures (11.7%), and corpus callosum (6.1%).

CONCLUSIONS

Infantile-onset saccade initiation delay is frequently associated with deficits in reflexive saccades and less frequently with impaired smooth ocular pursuit. Developmental delay, hypotonia, and ataxia occur frequently in ISID, suggesting more global brain impairment and not just a saccadic disorder.

Joubert syndrome presenting with motor delay and oculomotor apraxia

We describe two sisters who presented in early childhood with motor delay and unusual eye movements. Both demonstrated hypotonia and poor visual attention. The older girl at 14 weeks of age showed fine pendular horizontal nystagmus more pronounced on lateral gaze, but despite investigation with cranial MRI no diagnosis was reached. The birth of her younger sister four years later with a similar presentation triggered review of the sisters' visual behaviour. Each had developed an unusual but similar form of oculomotor apraxia (OMA) with head thrusts to maintain fixation rather than to change fixation. MRI of the older sibling demonstrated the characteristic "molar tooth sign" (MTS) of Joubert syndrome which was subsequently confirmed on MRI in the younger sibling. We discuss the genetically heterogeneous ciliopathies now grouped as Joubert syndrome and Related Disorders. Clinicians need to consider this group of disorders when faced with unusual eye movements in the developmentally delayed child.

Cerebellar hyperactivity during smooth pursuit eye movements in bipolar disorder

INTRODUCTION

Smooth pursuit eye movements (SPEM) are abnormal in individuals with schizophrenia and individuals with bipolar disorder. Functional imaging methods have revealed greater hippocampal activity and less frontotemporal, visual, and posterior cerebellar activity in individuals with schizophrenia when performing a SPEM task. The underlying neurobiology of SPEM deficits in bipolar disorder is unknown.

METHODS

Functional magnetic resonance imaging at 3T was performed on fourteen subjects with bipolar disorder and 14 subjects without psychiatric illness during a block design SPEM task. Clinical measures were assessed on the day of testing and related to imaging measures.

RESULTS

Subjects with bipolar disorder had greater hemodynamic response than control subjects in cerebellar vermis. Responses were associated with levels of depressive symptoms on the day of study.

DISCUSSION

Increased cerebellar vermis activity during the smooth pursuit eye movement task in individuals with bipolar disorder further implicates cerebellar involvement in bipolar disorder. Increased hemodynamic response within the hippocampus was not seen in these individuals and may be a finding specific to schizophrenia.

MRI with fibre tracking in Cogan congenital oculomotor apraxia

BACKGROUND

Congenital ocular motor apraxia (COMA) occasionally shares with Joubert syndrome (JS) and related disorders (JSRDs) a peculiar malformation, the 'molar tooth sign' (MTS). In JSRDs, the absence of superior cerebellar peduncles (SCP) decussation is reported.

OBJECTIVE

To investigate whether COMA demonstrates similar abnormal axonal pathways.

MATERIALS AND METHODS

Eight healthy age-matched controls, three children with clinical COMA and one child with clinical JSRD underwent examination with a 1.5-T MRI scanner. Diffusion-weighted imaging (DWI), colour-coded fractional anisotropy maps and three-dimensional diffusion tensor imaging (DTI) tractography of the cerebellorubral network were analyzed.

RESULTS

On DTI cartography, the 'red dot' originally supposed to represent the SCP decussation in the midbrain was present in controls as well in those with COMA but absent in the single case with JS. In none of the subjects including controls was 3-D FT able to depict the SCP decussation. When seeded, the red dot resulted in the ventral tegmental decussation (VTD). It was normal in controls and in patients with COMA but was absent in our single patient with JSRD. MTS was identified in alla patients with COMA and in the patient with JSRD.

CONCLUSION

MTS can be present in both COMA and JSRD but the underlying anatomy depicted by fibre tracking is distinct. The main difference is the integrity of the VTD in COMA.

Joubert Syndrome and related disorders

Joubert syndrome (JS) and related disorders (JSRD) are a group of developmental delay/multiple congenital anomalies syndromes in which the obligatory hallmark is the molar tooth sign (MTS), a complex midbrain-hindbrain malformation visible on brain imaging, first recognized in JS. Estimates of the incidence of JSRD range between 1/80,000 and 1/100,000 live births, although these figures may represent an underestimate. The neurological features of JSRD include hypotonia, ataxia, developmental delay, intellectual disability, abnormal eye movements, and neonatal breathing dysregulation. These may be associated with multiorgan involvement, mainly retinal dystrophy, nephronophthisis, hepatic fibrosis and polydactyly, with both inter- and intra-familial variability. JSRD are classified in six phenotypic subgroups: Pure JS; JS with ocular defect; JS with renal defect; JS with oculorenal defects; JS with hepatic defect; JS with orofaciodigital defects. With the exception of rare X-linked recessive cases, JSRD follow autosomal recessive inheritance and are genetically heterogeneous. Ten causative genes have been identified to date, all encoding for proteins of the primary cilium or the centrosome, making JSRD part of an expanding group of diseases called "ciliopathies". Mutational analysis of causative genes is available in few laboratories worldwide on a diagnostic or research basis. Differential diagnosis must consider in particular the other ciliopathies (such as nephronophthisis and Senior-Loken syndrome), distinct cerebellar and brainstem congenital defects and disorders with cerebro-oculo-renal manifestations. Recurrence risk is 25% in most families, although X-linked inheritance should also be considered. The identification of the molecular defect in couples at risk allows early prenatal genetic testing, whereas fetal brain neuroimaging may remain uninformative until the end of the second trimester of pregnancy. Detection of the MTS should be followed by a diagnostic protocol to assess multiorgan involvement. Optimal management requires a multidisciplinary approach, with particular attention to respiratory and feeding problems in neonates and infants. Cognitive and behavioral assessments are also recommended to provide young patients with adequate neuropsychological support and rehabilitation. After the first months of life, global prognosis varies considerably among JSRD subgroups, depending on the extent and severity of organ involvement.

A case of Joubert syndrome with features of ocular neovascularization

A 12-year-old boy with a diagnosis of Joubert syndrome with bilateral horizontal nystagmus was evaluated. Neovascularization over the iris and the pupillary border was observed on biomicroscopy. There was pigmentary retinal dystrophy in both eyes. Fundus fluorescein angiography revealed ischemic areas and fluorescein leakage due to retinal neovascularization in both eyes.

Ataxia, hyperpnoea and mental retardation: was it the molar tooth?

Joubert's syndrome is a rare autosomal recessive disease, which is under-diagnosed, associated with other brain and body malformations, and carries a poor prognosis. We describe a 6-year-old boy who presented with non-progressive instability of stance and gait, mental retardation and a new onset of generalised seizures with the typical brain imaging findings of Joubert's syndrome. We believe this is the first diagnosed case of Joubert's syndrome in Iraq.

Clinical and molecular features of Joubert syndrome and related disorders

Joubert syndrome (JBTS; OMIM 213300) is a rare, autosomal recessive disorder characterized by a specific congenital malformation of the hindbrain and a broad spectrum of other phenotypic findings that is now known to be caused by defects in the structure and/or function of the primary cilium. The complex hindbrain malformation that is characteristic of JBTS can be identified on axial magnetic resonance imaging and is known as the molar tooth sign (MTS); other diagnostic criteria include intellectual disability, hypotonia, and often, abnormal respiratory pattern and/or abnormal eye movements. In addition, a broad spectrum of other anomalies characterize Joubert syndrome and related disorders (JSRD), and may include retinal dystrophy, ocular coloboma, oral frenulae and tongue tumors, polydactyly, cystic renal disease (including cystic dysplasia or juvenile nephronophthisis), and congenital hepatic fibrosis. The clinical course can be variable, but most children with this condition survive infancy to reach adulthood. At least eight genes cause JSRD, with some genotype-phenotype correlations emerging, including the association between mutations in the MKS3 gene and hepatic fibrosis characteristic of the JSRD subtype known as COACH syndrome. Several of the causative genes for JSRD are implicated in other ciliary disorders, such as juvenile nephronophthisis and Meckel syndrome, illustrating the close association between these conditions and their overlapping clinical features that reflect a shared etiology involving the primary cilium.

Joubert syndrome: insights into brain development, cilium biology, and complex disease

Joubert syndrome (JS) is a primarily autosomal recessive condition characterized by hypotonia, ataxia, abnormal eye movements, and intellectual disability with a distinctive mid-hindbrain malformation (the "molar tooth sign"). Variable features include retinal dystrophy, cystic kidney disease, liver fibrosis and polydactyly. Recently, substantial progress has been made in our understanding of the genetic basis of JS, including identification of seven causal genes (NPHP1, AHI1, CEP290, RPGRIP1L, TMEM67/MKS3, ARL13B and CC2D2A). Despite this progress, the known genes account for <50% of cases and few strong genotype-phenotype correlations exist in JS; however, genetic testing can be prioritized based on clinical features. While all seven JS genes have been implicated in the function of the primary cilium/basal body organelle (PC/BB), little is known about how the PC/BB is required for brain, kidney, retina and liver development/function, nor how disruption of PC/BB function leads to diseases of these organs. Recent work on the function of the PC/BB indicates that the organelle is required for multiple signaling pathways including sonic hedgehog, WNT and platelet derived growth factor. Due to shared clinical features and underlying molecular pathophysiology, JS is included in the rapidly expanding group of disorders called ciliopathies. The ciliopathies are emerging as models for more complex diseases, where sequence variants in multiple genes contribute to the phenotype expressed in any given patient.

“Staircase” Saccadic Intrusions plus Transient Yoking and Neural Integrator Failure Associated with Cerebellar Hypoplasia: A Model Simulation

We present hypothesized ocular motor mechanisms of unique "staircase-like" sequences of saccadic intrusions in one direction that we have named, "staircase saccadic intrusions (SSI)," square-wave jerks/oscillations (SWJ/SWO), and transient failures of yoking and neural integrators in a patient with severe hypotonia, ataxic speech, motor and language developmental delays, and torticollis (Joubert syndrome). Brain magnetic resonance imaging showed hypoplasia of the cerebellar vermis and inferior cerebellar peduncles, abnormal superior cerebellar peduncles with deepening of the interpeduncular fossa, and enlargement of the fourth ventricle. During far and near fixation and smooth pursuit (rightward markedly better than leftward), the subject exhibited conjugate SSI (rightward more than leftward, with intersaccadic intervals equivalent to the normal 250 msec visual latency), SWJ, SWO, and uniocular, convergent and divergent saccades (including double saccades). Simulations using a behavioral ocular motor system model identified hypothetical mechanisms for SWJ, SWO, and SSI and ruled out the loss of efference copy as the cause. SSI may result from simultaneous dysfunctions: 1) a transient loss of accurate retinal-error information and/or sampled, reconstructed error; plus 2) a constant sampled, reconstructed retinal error that drives saccades.

Familial congenital oculomotor apraxia: clinical and electro-oculographic features

The electro-oculographic (EOG) features of both horizontal and vertical eye movements in congenital oculomotor apraxia (COMA) were not previously reported. A girl referred to the ophthalmologic department for abnormal eye movements was diagnosed as COMA. The same abnormal ocular movements were observed in her younger sister and her father who was unaware of his difficulties to initiate voluntary saccades. When performed, EOG recordings of all horizontal and vertical saccadic eye movements were severely altered whatever the age of the patient. Pursuit was normal for these patients. It confirms that the control of saccadic eye movements is still altered in adults in both directions horizontal and vertical that were never reported. EOG is necessary to rule out inherited form of this saccade initiation failure.

Ophthalmological findings in Joubert syndrome

PURPOSE

Joubert syndrome (JS) is an autosomal-recessive inherited complex malformation of the midbrain-hindbrain. It has been associated with ocular and oculomotor abnormalities. The aim of our study was to extend the ophthalmic knowledge in JS and to add new findings.

METHODS

In a retrospective study, 10 consecutive patients, who met the revised diagnostic criteria of JS were included. Mutation analysis was carried out in all the cases. Each patient underwent a comprehensive neuro-ophthalmological examination.

RESULTS

Bilateral drusen of the optic disc were found in two patients. Four patients showed bilateral morphological and functional signs of retinal dystrophy (CEP290 mutation in two cases and AHI1 mutation in one case). In nine patients performance during smooth pursuit, saccades, and vestibulo-ocular reflex (VOR) cancellation was poor.

CONCLUSIONS

To the best of our knowledge, the association of optic disc drusen with JS has not yet been described. In support of the earlier findings, decreased smooth pursuit and VOR cancellation, as well as partial-to-complete oculomotor apraxia seem to be the key oculomotor features of JS. Genotype-phenotype correlations showed the predictive value of CEP290 and AHI1 mutations for retinal involvement.

Ophthalmic features of Joubert syndrome

PURPOSE

Joubert syndrome (Online Mendelian Inheritance in Man 213300) is a rare autosomal recessive congenital malformation of the brainstem and cerebellar vermis. Diagnosis is based on characteristic clinical features (e.g., hypotonia, episodic hyperpnea, developmental delay, progressive ataxia) and is confirmed by distinctive neuroradiologic findings (e.g., the "molar tooth" sign). Variable ophthalmic features have been mentioned in prior reports; however, most do not detail eye findings and the few that do were before the publication of suggested diagnostic criteria. The objective of the current study is to describe the ophthalmic phenotype in a cohort of patients with Joubert syndrome for whom the diagnosis was made using current diagnostic criteria.

DESIGN

Prospective case series.

PARTICIPANTS

Eight children diagnosed clinically with radiologic confirmation.

METHODS

Ophthalmic examination and visual electrophysiology.

MAIN OUTCOME MEASURES

Ocular and oculomotor examination (as allowed by patient cooperation), electroretinography, flash visual-evoked potential (fVEP).

RESULTS

Patients' ages ranged from 7 months to 10 years. Saccadic dysfunction was observed in all cooperative patients (6/6); compensatory head thrusts or turns were present in all except the youngest patient (7 months of age). Most patients (5/8) had primary-position nystagmus (see-saw in 3/5). Abnormal pursuit (3/7) and a dystrophic retinal appearance (3/8) were also seen. One patient had bilateral asymmetric ptosis with unilateral lid elevation during ipsilateral abduction. Electroretinography findings were normal for all 8 patients. Seven patients underwent fVEP; 6 were abnormal (asymmetric) and one was not interpretable because of study artifact.

CONCLUSIONS

Ophthalmologists should be aware that saccadic dysfunction (typically with head thrusts) and primary position nystagmus (typically see-saw) in a developmentally delayed child suggest the diagnosis of Joubert syndrome, especially if a dystrophic retinal appearance is also present. Our findings of asymmetric fVEPs and see-saw nystagmus suggest an abnormality in optic nerve decussation, consistent with the concept that impaired axonal guidance occurs in patients with Joubert syndrome.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Joubert syndrome (and related disorders) (OMIM 213300)

Joubert syndrome (JS) and related disorders are characterized by the 'molar tooth sign' (cerebellar vermis hypoplasia and brainstem anomalies) on MRI, hypotonia, developmental delay, ataxia, irregular breathing pattern and abnormal eye movements. Combinations of additional features such as polydactyly, ocular coloboma, retinal dystrophy, renal disease, hepatic fibrosis, encephalocele, and other brain malformations define clinical sub-types. Recent identification of the NPHP1, AHI1, and CEP290 genes has started to reveal the molecular basis of JS, which may implicate the primary cilium in these disorders. Additional genes remain to be identified.

Identification of the first AHI1 gene mutations in nephronophthisis-associated Joubert syndrome

Joubert syndrome (JBTS) is an autosomal recessive multisystem disease characterized by cerebellar vermis aplasia, mental retardation, muscular hypotonia, an irregular breathing pattern in the neonatal period and abnormal eye movements. Some individuals have progressive renal failure characterized by nephronophthisis (NPHP) and/or retinal dystrophy. Homozygous deletions of NPHP1 on chromosome 2q13 have been identified in individuals with NPHP-associated JBTS. Recently, mutations in AHI1 on chromosome 6q23.3 were found in JBTS patients without NPHP. Here, by direct sequencing, we identify novel truncating mutations within AHI1 in affected patients from two families. One patient had the association of JBTS and NPHP with chronic renal failure. This is the first report of AHI1 mutations causing JBTS associated with NPHP, confirming the clinical and genetic heterogeneity of NPHP.

The NPHP1 gene deletion associated with juvenile nephronophthisis is present in a subset of individuals with Joubert syndrome

Joubert syndrome (JS) is an autosomal recessive multisystem disease characterized by cerebellar vermis hypoplasia with prominent superior cerebellar peduncles (the "molar tooth sign" [MTS] on axial magnetic resonance imaging), mental retardation, hypotonia, irregular breathing pattern, and eye-movement abnormalities. Some individuals with JS have retinal dystrophy and/or progressive renal failure characterized by nephronophthisis (NPHP). Thus far, no mutations in the known NPHP genes, particularly the homozygous deletion of NPHP1 at 2q13, have been identified in subjects with JS. A cohort of 25 subjects with JS and either renal and/or retinal complications and 2 subjects with only juvenile NPHP were screened for mutations in the NPHP1 gene by standard methods. Two siblings affected with a mild form of JS were found to have a homozygous deletion of the NPHP1 gene identical, by mapping, to that in subjects with NPHP alone. A control subject with NPHP and with a homozygous NPHP1 deletion was also identified, retrospectively, as having a mild MTS and borderline intelligence. The NPHP1 deletion represents the first molecular defect associated with JS in a subset of mildly affected subjects. Cerebellar malformations consistent with the MTS may be relatively common in patients with juvenile NPHP without classic symptoms of JS.

Congenital ocular motor apraxia associated with idiopathic generalized epilepsy in monozygotic twins

Identical female twins (age 11 years) with congenital ocular motor apraxia and generalized idiopathic epilepsy are reported. Their presenting symptoms were a long history of abnormal head and eye movements. One twin developed partial sensory seizures. The patients underwent 16-channel EEG, electro-oculographic recordings, MRI of the brain, and genetic and metabolic investigations. EEG findings were consistent with idiopathic generalized epilepsy. Electrooculographic recordings of the saccades confirmed an inability to elicit horizontal saccades without preceding head movement; saccades to the left were better than saccades to the right. MR scans for one twin showed normal findings, however, for the twin who had meningitis they revealed asymmetry between the right and left temporal lobes but no specific abnormality. DNA analysis using a series of autosomal polymorphic markers confirmed the monozygocity of the twins. White blood cell enzyme analysis excluded Sandhoff disease, Tay-Sachs disease, GM1 gangliosidosis, metacromatic leucodystrophy, Gaucher disease, Niemann-Pick disease (A and B), and Krabbe leucodystrophy. Albumin and immunoglobulin (IgA, IgG, and IgM) levels were normal. It is concluded that autosomal recessive inheritance seems the most likely explanation here, as recent studies have found insertion and missense mutations of the aprataxin gene which have been related to an early onset form of ataxia with ocular motor apraxia and hypoalbuminaemia.

Congenital malformations of the human brainstem

Congenital disorders of the brainstem often result in multiple severe neurodevelopmental problems. With the advent of magnetic resonance imaging and discovery of genes directing brainstem formation, a more coherent clinical picture of these disorders is emerging. Proper evaluation, management, and counseling for these disorders rests on the clinician having a framework through which to approach them.

Quantitative assessment of brainstem development in Joubert syndrome and Dandy-Walker syndrome

Key features of Joubert syndrome include developmental delay, hypotonia, hyperpnea and apnea, oculomotor apraxia, and the presence of the molar tooth sign on axial imaging through the brainstem isthmus--the junction of the pons and mesencephalon. Interestingly, 1 in 10 patients with Joubert syndrome has abnormal cerebrospinal fluid collections misdiagnosed as Dandy-Walker variants. Because of important differences in patient management, genetic counseling, and prognosis between these conditions, we undertook a study to determine if the brainstem isthmus is normal in Dandy-Walker syndrome. Using standard landmarks, we evaluated development of the isthmus in normal subjects and in subjects with Joubert syndrome and Dandy-Walker syndrome. Four of five brainstem measures increased with age in normal subjects. In subjects with Joubert syndrome, the depth and length of the interpeduncular fossa were increased, and the width of the isthmus was decreased. In subjects with Dandy-Walker syndrome, the width of the brainstem isthmus was normal, and the molar tooth sign was absent. Although the pons can be hypoplastic in Dandy-Walker syndrome, we conclude that the pontomesencephalic junction is normal. Thus, the molar tooth sign can effectively distinguish between Joubert and Dandy-Walker syndromes. Genetic heterogeneity or epigenetic factors may account for abnormal cerebrospinal fluid collections in some cases of Joubert syndrome.

Ocular motor disorders

Our detailed understanding of the physiology and anatomy of the ocular motor system allows an accurate differential diagnosis of pathological eye movement patterns. This review covers important clinical studies and studies in basic research relevant for the neurologist published during the past year.

Autosomal recessive cerebellar ataxia with oculomotor apraxia (ataxia-telangiectasia-like syndrome) is linked to chromosome 9q34

Ataxia with oculomotor apraxia (ataxia-telangiectasia-like syndrome [AOA]; MIM 208920) is an autosomal recessive disorder characterized by ataxia, oculomotor apraxia, and choreoathetosis. These neurological features resemble those of ataxia-telangiectasia (AT), but in AOA there are none of the extraneurological features of AT, such as immunodeficiency, neoplasia, chromosomal instability, or sensitivity to ionizing radiation. It is unclear whether these patients have a true disorder of chromosomal instability or a primary neurodegenerative syndrome, and it has not been possible to identify the defective gene in AOA, since the families have been too small for linkage analysis. We have identified a new family with AOA, and we show that the patients have no evidence of chromosomal instability or sensitivity to ionizing radiation, suggesting that AOA in this family is a true primary cerebellar ataxia. We have localized the disease gene, by linkage analysis and homozygosity mapping, to a 15.9-cM interval on chromosome 9q34. This work will ultimately allow the disease gene to be identified and its relevance to other types of autosomal recessive cerebellar ataxias to be determined.

Nystagmus

This report reviews the recent contributions to the field of pathologic nystagmus. The classification and nomenclature of nystagmus with onset in infancy is controversial. Because there are differences in nystagmus forms between patients with idiopathic nystagmus and those with nystagmus associated with afferent sensory defects, a distinction between these two nystagmus types is proposed. The distinctions are also helpful for clinicians, because these separate entities imply different diagnostic evaluations and visual prognosis. Recent studies have confirmed that periodic alternating nystagmus is detected more easily if the patient is evaluated for a longer time period and occurs more commonly than previously thought. Psychophysical investigations indicate that extraretinal signals play an important role in suppression of oscillopsia in infantile nystagmus. Genetic analysis recently has allowed identification of genes of X-linked idiopathic nystagmus and achromatopsia.