Leber's congenital amaurosis: an update

Electroretinography in congenital nystagmus patients with a normal fundus examination

PURPOSE

To identify the ophthalmic causes of congenital nystagmus with normal eye examination by electroretinography (ERG).

STUDY DESIGN

Retrospective observational study.

METHODS

We reviewed the medical records of patients younger than 6 months of age who presented between June 2008 and November 2011 with nystagmus and no other neurological signs following an otherwise normal eye examination. A complete ophthalmic examination and ERG (Nicolet Bravo system; Nicolet Biomedial & RETIscan; Roland Instruments), fundus photography, and Ishihara color test were performed to identify any ophthalmic causes of congenital nystagmus.

RESULTS

Thirty-three patients met the criteria. Rod dysfunction was diagnosed in 4 patients (12.1%), cone dysfunction in 2 patients (6.1%), and cone-rod dysfunction in 1 patient (3.0%). The results of ERG were negative in 2 patients (6.1%). Idiopathic infantile nystagmus was diagnosed in the remaining 24 patients (72.7%) based on their normal ERG examination.

CONCLUSIONS

In Korean congenital nystagmus patients with a normal fundus examination, achromatopsia and Leber's congenital amaurosis are uncommon causes. ERG is needed to make a definite diagnosis and provide prognostic information in congenital idiopathic nystagmus patients with a normal fundus examination.

Optical coherence tomography in children with inherited retinal disease

Recent advances have led to therapeutic options becoming available for people with inherited retinal disease. In particular, gene therapy has been shown to hold great promise for slowing vision loss from inherited retinal disease. Recent studies suggest that gene therapy is likely to be most effective when implemented early in the disease process, making consideration of paediatric populations important. It is therefore necessary to have a comprehensive understanding of retinal imaging in children with inherited retinal diseases, in order to monitor disease progression and to determine which early retinal biomarkers may be used as outcome measures in future clinical trials. In addition, as many optometrists will review children with an inherited retinal disease, an understanding of the expected imaging outcomes can improve clinical care. This review focuses on the most common imaging modality used in research assessment of paediatric inherited retinal diseases: optical coherence tomography. Optical coherence tomography findings can be used in both the clinical and research setting. In particular, the review discusses current knowledge of optical coherence tomography findings in eight paediatric inherited retinal diseases - Stargardt disease, Bests disease, Leber's congenital amaurosis, choroideremia, RPGR related retinitis pigmentosa, Usher syndrome, X-linked retinoschisis and, Batten disease.

The Clinical Findings, Pathogenic Variants, and Gene Therapy Qualifications Found in a Leber Congenital Amaurosis Phenotypic Spectrum Patient Cohort

This retrospective study examines the clinical characteristics and underlying genetic variants that exist in a Leber congenital amaurosis (LCA) patient cohort evaluated at the inherited retinal disease (IRD) clinic at the University of Minnesota (UMN)/M Health System. Our LCA cohort consisted of 33 non-syndromic patients and one patient with Joubert syndrome. We report their relevant history, clinical findings, and genetic testing results. We monitored disease presentation utilizing ocular coherence tomography (OCT) and fundus autofluorescence (FAF). Electroretinogram testing (ERG) was performed in patients when clinically indicated. Next-generation sequencing (NGS) and genetic counseling was offered to all evaluated patients. Advanced photoreceptor loss was noted in 85.7% of the subjects. All patients who underwent FAF had findings of either a ring of macular hypo/hyper AF or peripheral hypo-AF. All patients had abnormal ERG findings. A diagnostic genetic test result was identified in 74.2% of the patients via NGS single-gene testing or panel testing. Two patients in our cohort qualified for Luxturna® and both received treatment at the time of this study. These data will help IRD specialists to understand the genetic variants and clinical presentations that characterize our patient population in the Midwest region of the United States.

Eyes on CHARGE syndrome: Roles of CHD7 in ocular development

The development of the vertebrate visual system involves complex morphogenetic interactions of cells derived from multiple embryonic lineages. Disruptions in this process are associated with structural birth defects such as microphthalmia, anophthalmia, and coloboma (collectively referred to as MAC), and inherited retinal degenerative diseases such as retinitis pigmentosa and allied dystrophies. MAC and retinal degeneration are also observed in systemic congenital malformation syndromes. One important example is CHARGE syndrome, a genetic disorder characterized by coloboma, heart defects, choanal atresia, growth retardation, genital abnormalities, and ear abnormalities. Mutations in the gene encoding Chromodomain helicase DNA binding protein 7 (CHD7) cause the majority of CHARGE syndrome cases. However, the pathogenetic mechanisms that connect loss of CHD7 to the ocular complications observed in CHARGE syndrome have not been identified. In this review, we provide a general overview of ocular development and congenital disorders affecting the eye. This is followed by a comprehensive description of CHARGE syndrome, including discussion of the spectrum of ocular defects that have been described in this disorder. In addition, we discuss the current knowledge of CHD7 function and focus on its contributions to the development of ocular structures. Finally, we discuss outstanding gaps in our knowledge of the role of CHD7 in eye formation, and propose avenues of investigation to further our understanding of how CHD7 activity regulates ocular and retinal development.

Sensing through Non-Sensing Ocular Ion Channels

Ion channels are membrane-spanning integral proteins expressed in multiple organs, including the eye. In the eye, ion channels are involved in various physiological processes, like signal transmission and visual processing. A wide range of mutations have been reported in the corresponding genes and their interacting subunit coding genes, which contribute significantly to an array of blindness, termed ocular channelopathies. These mutations result in either a loss- or gain-of channel functions affecting the structure, assembly, trafficking, and localization of channel proteins. A dominant-negative effect is caused in a few channels formed by the assembly of several subunits that exist as homo- or heteromeric proteins. Here, we review the role of different mutations in switching a “sensing” ion channel to “non-sensing,” leading to ocular channelopathies like Leber’s congenital amaurosis 16 (LCA16), cone dystrophy, congenital stationary night blindness (CSNB), achromatopsia, bestrophinopathies, retinitis pigmentosa, etc. We also discuss the various in vitro and in vivo disease models available to investigate the impact of mutations on channel properties, to dissect the disease mechanism, and understand the pathophysiology. Innovating the potential pharmacological and therapeutic approaches and their efficient delivery to the eye for reversing a “non-sensing” channel to “sensing” would be life-changing.

A Multidimensional, Multisensory and Comprehensive Rehabilitation Intervention to Improve Spatial Functioning in the Visually Impaired Child: A Community Case Study

Congenital visual impairment may have a negative impact on spatial abilities and result in severe delays in perceptual, social, motor, and cognitive skills across life span. Despite several evidences have highlighted the need for an early introduction of re-habilitation interventions, such interventions are rarely adapted to children’s visual capabilities and very few studies have been conducted to assess their long-term efficacy. In this work, we present a case study of a visually impaired child enrolled in a newly developed re-habilitation intervention aimed at improving the overall development through the diversification of re-habilitation activities based on visual potential and developmental profile, with a focus on spatial functioning. We argue that intervention for visually impaired children should be (a) adapted to their visual capabilities, in order to increase re-habilitation outcomes, (b) multi-interdisciplinary and multidimensional, to improve adaptive abilities across development, (c) multisensory, to promote the integration of different perceptual information coming from the environment.

Intraocular Lens Dislocation into the Anterior Chamber because of Repeated Eye-Poking in a Patient with Leber's Congenital Amaurosis

The dislocation of a posterior chamber intraocular lens (PC IOL) because of constant eye rubbing is unusual and has never been reported in a child with Leber's congenital amaurosis (LCA). A 4-year-old full-term girl with an ocular history of LCA presented to the emergency room with a single-piece PC IOL dislocated into the anterior chamber (AC) of the left eye. There was no history of trauma or any other surgical intervention. A specific behavior known as Franceschetti's oculo-digital sign is a characteristic feature of LCA; this sign consists of repeated pressing, poking, and rubbing of the eyes with knuckles and fingers to stimulate the photoreceptors. This behavior caused the dislocation of the PC IOL into the AC. The dislocated IOL was explanted, and the patient was provided with aphakic glasses.

Genetic testing for Leber congenital amaurosis

We studied the scientific literature and disease guidelines in order to summarize the clinical utility of genetic testing for Leber congenital amaurosis (LCA). LCA is mostly inherited in an autosomal recessive manner, rarely in an autosomal dominant manner, with an overall prevalence of 2-3/100,000 live births, and is caused by mutations in the AIPL1, CEP290, CRB1, CRX, GDF6, GUCY2D, IFT140, IMPDH1, IQCB1, KCNJ13, LCA5, LRAT, NMNAT1, RD3, RDH12, RPE65, RPGRIP1, SPATA7 and TULP1 genes. Clinical diagnosis involves ophthalmological examination and electrophysiological testing (electroretinography - ERG). The genetic test is useful for confirmation of diagnosis, differential diagnosis, couple risk assessment and access to clinical trials.

Correlation of ultra-widefield fundus autofluorescence patterns with the underlying genotype in retinal dystrophies and retinitis pigmentosa

PURPOSE

Ultra-widefield fundus autofluorescence (UW-FAF) allows the characterization of the peripheral retinal features of vitreoretinal diseases. The purpose of this study was to examine possible genotypic/phenotypic correlations of UW-FAF patterns in patients with a variety of retinal dystrophies and retinitis pigmentosa (RP).

METHODS

An IRB-approved retrospective consecutive case series study was performed of genetically characterized retinal dystrophy or RP patients who underwent UW-FAF imaging. UW-FAF was performed with the Optos 200Tx system. Clinical variables, genotypic analysis, and phenotypic characteristics were reviewed.

RESULTS

Seventeen patients were identified who had identified mutations in retinal dystrophy or RP genes and who also had undergone UW-FAF. Three patients had X-linked RP with RPGR mutations. Six patients had autosomal dominant RP (four with RHO mutations and one with a PRPF31 mutation, and one with RDS/PRPH2 mutation). Four patients had autosomal recessive RP (four with USH2A mutations). Three patients had Leber Congenital Amaurosis (LCA) with mutations including CRB1, CEP290, and RPGRIP1. Macular hyperautofluorescence was noted in all patients. A ring of hyperautofluorescence was clear in patients with RHO and USH2A mutations, and patients with USH2A mutations demonstrated a second ring of hyperautofluorescence. In the periphery, patients with RHO or RPGR mutations exhibited hyperautofluorescence with patchy areas of hypoautofluorescence. Patients with USH2A mutations had a distinctive pattern of diffuse and homogeneous peripheral hypoautofluorescence.

CONCLUSION

UW-FAF may provide important information to facilitate diagnosis and further research is needed to better characterize this technology as an imaging biomarker for genotype association in retinal dystrophies and RP.

A Novel KCNJ13 Nonsense Mutation and Loss of Kir7.1 Channel Function Causes Leber Congenital Amaurosis (LCA16)

Mutations in the KCNJ13 gene that encodes the inwardly rectifying potassium channel Kir7.1 cause snowflake vitreoretinal degeneration (SVD) and leber congenital amaurosis (LCA). Kir7.1 controls the microenvironment between the photoreceptors and the retinal pigment epithelium (RPE) and also contributes to the function of other organs such as uterus and brain. Heterologous expressions of the mutant channel have suggested a dominant-negative loss of Kir7.1 function in SVD, but parallel studies in LCA16 have been lacking. Herein, we report the identification of a novel nonsense mutation in the second exon of the KCNJ13 gene that leads to a premature stop codon in association with LCA16. We have determined that the mutation results in a severe truncation of the Kir7.1 C-terminus, alters protein localization, and disrupts potassium currents. Coexpression of the mutant and wild-type channel has no negative influence on the wild-type channel function, consistent with the normal clinical phenotype of carrier individuals. By suppressing Kir7.1 function in mice, we were able to reproduce the severe LCA electroretinogram phenotype. Thus, we have extended the observation that Kir7.1 mutations are associated with vision disorders to include novel insights into the molecular mechanism of disease pathobiology in LCA16.

Diagnostic application of an extensive gene panel for Leber congenital amaurosis with severe genetic heterogeneity

Leber congenital amaurosis (LCA) is a genetically heterogeneous disorder and the most severe form of inherited retinal dystrophy. We report results of a diagnostic application of an extensive gene panel composed of 204 retinal dystrophy-related genes and discuss its feasibility as a diagnostic tool. Nineteen unrelated LCA patients were included in the study: two patients for validation purposes of our gene panel, 15 previously analyzed patients with no identified mutations, and two previously unanalyzed patients. Genetic diagnosis for each patient was conducted according to whether the variants were consistent with the known inheritance pattern of each gene. We identified two heterozygous or homozygous pathogenic variants in seven of 19 patients. On the basis of mutation information, clinical features were re-reviewed, and clinical diagnoses for two patients were revised from LCA to LCA-related disorders. In addition, a coverage simulation was performed to determine the optimal depth of coverage of the gene panel. Using our gene panel, we diagnosed LCA and LCA-related disorders in 36.8% of patients and one or more deleterious variants or variants of unknown significance in 89.5% of patients. Molecular diagnosis using this extensive gene panel is expected to facilitate diagnosis of retinal dystrophy and help provide proper treatment to patients, although further analyses is needed for a complete clinical validation.

Pupillometric analysis for assessment of gene therapy in Leber Congenital Amaurosis patients

BACKGROUND

Objective techniques to assess the amelioration of vision in patients with impaired visual function are needed to standardize efficacy assessment in gene therapy trials for ocular diseases. Pupillometry has been investigated in several diseases in order to provide objective information about the visual reflex pathway and has been adopted to quantify visual impairment in patients with Leber Congenital Amaurosis (LCA). In this paper, we describe detailed methods of pupillometric analysis and a case study on three Italian patients affected by Leber Congenital Amaurosis (LCA) involved in a gene therapy clinical trial at two follow-up time-points: 1 year and 3 years after therapy administration.

METHODS

Pupillary light reflexes (PLR) were measured in patients who had received a unilateral subretinal injection in a clinical gene therapy trial. Pupil images were recorded simultaneously in both eyes with a commercial pupillometer and related software. A program was generated with MATLAB software in order to enable enhanced pupil detection with revision of the acquired images (correcting aberrations due to the inability of these severely visually impaired patients to fixate), and computation of the pupillometric parameters for each stimulus. Pupil detection was performed through Hough Transform and a non-parametric paired statistical test was adopted for comparison.

RESULTS

The developed program provided correct pupil detection also for frames in which the pupil is not totally visible. Moreover, it provided an automatic computation of the pupillometric parameters for each stimulus and enabled semi-automatic revision of computerized detection, eliminating the need for the user to manually check frame by frame. With reference to the case study, the amplitude of pupillary constriction and the constriction velocity were increased in the right (treated eye) compared to the left (untreated) eye at both follow-up time-points, showing stability of the improved PLR in the treated eye.

CONCLUSIONS

Our method streamlined the pupillometric analyses and allowed rapid statistical analysis of a range of parameters associated with PLR. The results confirm that pupillometry is a useful objective measure for the assessment of therapeutic effect of gene therapy in patients with LCA.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00516477.

Leber congenital amaurosis associated with Chiari I malformation: Two cases and a review of the literature

OBJECTIVE

Leber congenital amaurosis (LCA) is a rare, clinically and genetically heterogeneous disorder characterized by severe loss of vision in the first year of life, affecting approximately 3000 people in the United States. Some LCA patients manifest developmental abnormalities of the central nervous system (CNS) and neuroradiological studies have revealed a variety of cerebral anomalies in association with LCA; however, Chiari I malformations (CMI) have never been described.

CASE DESCRIPTION

We report two sisters who were referred to the pediatric neurosurgery clinic for evaluation of CMI. The elder sister presented with convergence nystagmus from 3 months of age and magnetic resonance imaging (MRI) demonstrated evidence of significant CMI. Her younger sister began developing nystagmus at 4 months of age. Both had symptomatic progression and underwent suboccipital decompression. Both were subsequently diagnosed with LCA. Case specifics and imaging findings are presented.

CONCLUSIONS

CMI have been found in association with several genetic syndromes, but not with LCA. These patients represent the first reported cases of CMI with LCA and suggest an additional potential CNS anomaly. The unique occurrence in siblings and the association with another inherited disorder are suggestive of a genetic basis for CMI.

Gene therapy rescues cone structure and function in the 3-month-old rd12 mouse: a model for midcourse RPE65 leber congenital amaurosis

PURPOSE

RPE65 function is necessary in the retinal pigment epithelium (RPE) to generate chromophore for all opsins. Its absence results in vision loss and rapid cone degeneration. Recent Leber congenital amaurosis type 2 (LCA with RPE65 mutations) phase I clinical trials demonstrated restoration of vision on RPE65 gene transfer into RPE cells overlying cones. In the rd12 mouse, a naturally occurring model of RPE65-LCA early cone degeneration was observed; however, some peripheral M-cones remained. A prior study showed that AAV-mediated RPE65 expression can prevent early cone degeneration. The present study was conducted to test whether the remaining cones in older rd12 mice can be rescued.

METHODS

Subretinal treatment with the scAAV5-smCBA-hRPE65 vector was initiated at postnatal day (P)14 and P90. After 2 months, electroretinograms were recorded, and cone morphology was analyzed by using cone-specific peanut agglutinin and cone opsin-specific antibodies.

RESULTS

Cone degeneration started centrally and spread ventrally, with cells losing cone-opsin staining before that for the PNA-lectin-positive cone sheath. Gene therapy starting at P14 resulted in almost wild-type M- and S-cone function and morphology. Delaying gene-replacement rescued the remaining M-cones, and most important, more M-cone opsin-positive cells were identified than were present at the onset of gene therapy, suggesting that opsin expression could be reinitiated in cells with cone sheaths.

CONCLUSIONS

The results support and extend those of the previous study that gene therapy can stop early cone degeneration, and, more important, they provide proof that delayed treatment can restore the function and morphology of the remaining cones. These results have important implications for the ongoing LCA2 clinical trials.

Evaluation of 9-cis-retinyl acetate therapy in Rpe65-/- mice

PURPOSE

Mice lacking retinal pigment epithelium-specific 65-kDa protein (RPE65) develop retinopathy and blindness resembling Leber congenital amaurosis. Effects of 9-cis-retinyl acetate (9-cis-R-Ac) on visual function and retinopathy progression were tested in Rpe65(-/-) mice.

METHODS

Young C57Bl/6 mice were given 9-cis-R-Ac in each of four different oil-based vehicle solutions by gastric gavage to identify the vehicle most suitable for drug delivery by measuring retinoid levels in plasma. Then doses of 9-cis-R-Ac ranging from 1 to 100 mg/kg were administered to 5- to 12-week-old Rpe65(-/-) mice by different treatment regimens, including single doses and either intermittent or daily doses for various periods up to 8 weeks. Retinoid effects on visual function were evaluated by electroretinography, retinoid analyses, histologic methods, and vision-dependent behavioral testing.

RESULTS

Soybean oil vehicle provided the highest 9-cis-R-Ac metabolite levels in plasma. Single doses of 9-cis-R-Ac (6.25-50 mg/kg) provided significant dose-dependent improvement in electroretinographic responses. Well-tolerated daily doses (1-12.5 mg/kg) for 2 weeks induced remarkable improvement of retinal function. Significant dose-dependent improvement of electroretinographic responses was observed 6 days after administration of 9-cis-R-Ac daily for 3 days at 1 to 12.5 mg/kg. Mice given either daily or intermittent 9-cis-R-Ac treatment at 1 and 4 mg/kg and evaluated 8 weeks later displayed dose-dependent improvement of retinal function and morphology, whereas retinal function deteriorated in control animals. Treated mice also performed better than control animals in vision-dependent behavioral tests.

CONCLUSIONS

Treatment with 9-cis-R-Ac improves visual function and preserves retinal morphology in Rpe65(-/-) mice.

LCA5, a rare genetic cause of leber congenital amaurosis in Koreans

PURPOSE

Leber congenital amaurosis (LCA), the most severe form of inherited retinal dystrophy, is a genetically heterogenous disorder and more than nine genes only account for about half of LCA cases. Recently, LCA5 was identified as a rare genetic cause of LCA. Here, we analyzed the LCA5 gene in 14 LCA patients with no mutation identified in any other known LCA genes and 3 patients with one unclassified missense variant in RPGRIP1.

METHODS

We analyzed all exons and flanking regions of the LCA5 gene using direct sequencing. We included 170 control subjects in this study to screen novel sequence variant and analyzed the functional effect of a missense variant using in-silico prediction.

RESULTS

No pathogenic mutation in LCA5 was found in our seventeen patients including 3 patients with one unclassified missense variant in RPGRIP1. We identified one novel missense variant, c.1642C>T (p.Pro548Ser), in exon 9. We considered it benign because it was found in control subjects and predicted not to be harmful to protein function on in-silico prediction. We identified another intronic variant, which has been confirmed to be benign through mRNA analysis.

CONCLUSIONS

This result shows that mutation in LCA5 is likely to be a rare genetic cause in Koreans and suggests that further investigation to identify other causative genes is necessary in Koreans.

Ciliary syndromes and treatment

Abnormal visceral patterning has been known for centuries. However, it has not been associated with ciliary dysfunction until recently. Overlapping clinical entities including situs inversus, certain infertility disorders, as well as chronic respiratory infections have their roots in abnormal ciliary function. Current research focuses on causative factors and genes involved in signal transduction pathways that define ciliary function and structure, as well as treatment. In this review, attempts are made to outline selected, yet key topics related to ciliary function in health and disease.

Leber's congenital amaurosis: is there an autistic component?

There is much evidence in the literature suggesting that children with congenital blindness can also present autistic like features. The aetiopathogenetic and clinical significance of this association is still unclear. Given the central role played by vision in development, we set out to establish the significance of autistic-like behaviours in children with early-onset severe visual impairment. Our sample comprised 24 children (13 males, 11 females; mean age 5y 2mo; range 2-11y) affected by Leber's congenital amaurosis (LCA). The results of our administration of a modified Childhood Autism Rating Scale--excluding item VII (Visual Responsiveness)--showed that only four of the children gave an overall score indicating the presence of autism (moreover, of mild/moderate degree). Hardly any of the children in our LCA sample presented major dysfunctions in their relationships with other people or in their social and emotional responsiveness, thus allowing us to exclude a genuine comorbidity with a picture of autism. Indeed, the risk facing the visually impaired child seems to concern their early interactive experiences, which may be affected by their inability to connect with others, and may be prevented through the development of specific strategies of intervention.

AAV-mediated gene transfer for retinal diseases

Vectors based on the adeno-associated virus (rAAV) are able to transduce the retina of animal models, including non-human primates, for a long-term period, safely and at sustained levels. The ability of the various rAAV serotypes to transduce retinal target cells has been exploited to successfully transfer genes to photoreceptors, retinal pigment epithelium and the inner retina, which are affected in many inherited and non-inherited blinding diseases. rAAV-mediated, constitutive and regulated gene expression at therapeutic levels has been achieved in the retina of animal models, thus providing proof-of-principle of gene therapy efficacy and safety in models of dominant and recessive retinal disorders. In addition, gene transfer of molecules with either neurotrophic or antiangiogenic properties provides useful alternatives to the classic gene replacement for treatment of both mendelian and complex traits affecting the retina. Years of successful rAAV-mediated gene transfer to the retina have resulted in restoration of vision in dogs affected with congenital blindness. This has paved the way to the first attempts at treating inherited retinal diseases in humans with rAAV. Although the results of rAAV clinical trials for non-retinal diseases give a warning that the outcome of viral-mediated gene transfer in humans may be different from that predicted based on results in other species, the immune privilege of the retina combined with the versatility of rAAV serotypes may ultimately provide the first successful treatment of human inherited diseases using rAAV.

Insights into X-linked retinitis pigmentosa type 3, allied diseases and underlying pathomechanisms

In the past decade, we have witnessed great advances in the identification of genes underlying numerous neurodegenerative diseases and the stark complexity determining genotype-phenotype relationships that lead to the impairment, and ultimately, premature death of neurons. However, significant challenges lie ahead in understanding the pathobiological and spatiotemporal processes triggered by genetic lesions underlying neurodegenerative disorders. Neuroretinal dystrophies occupy a prominent place among neurodegenerative diseases, because of the large number and prevalence of disease-causing genes, the diverse functions, the wealth of allelic, non-allelic and clinical heterogeneities determining the phenotypic expressivity and penetrance of the disease and the ease of use of animal models to probe gene function and disease pathogenesis in a well-defined neuroretinal circuitry. Retinitis pigmentosa (RP) has a prevalence of about one in 4000. RP is a retinal dystrophy leading primarily to the progressive death of photon-capturing neurons--the rod photoreceptors. X-linked retinitis pigmentosa type 3 (XlRP3) accounts up to 14% of all RP cases, higher than any other single RP locus identified to date, and considered to be the most severe of all RP cases. The XlRP3 encodes the retinitis pigmentosa GTPase regulator (RPGR). RPGR interacts with the RPGR interacting protein-1 (RPGRIP1). Mutations in RPGRIP1 cause Leber's congenital amaurosis. This review highlights the progress devoted to understand the pathogenesis associated with XlRP3 and allied disorders and, concepts, trends and discrepancies emerging as molecular, subcellular and physiological processes linked to RPGR and RPGRIP1-protein network begin to be elucidated, and that may serve as a paradigm for other biological processes and neurodegenerative diseases.

Phenotype of three consanguineous Tunisian families with early-onset retinal degeneration caused by an R91W homozygous mutation in the RPE65 gene

PURPOSE

To identify the genetic defect, and to phenotype, three consanguineous Tunisian families presenting with early-onset retinal degeneration (EORD).

METHODS

All accessible family members were included. They underwent blood sampling and ophthalmological examination including, when possible, full-field ERG and pupillometry. A genome-wide linkage analysis was initiated. Mutation analysis of the RPE65 gene within the linked interval was performed by bi-directional sequencing.

RESULTS

Eleven out of 53 examined members were clinically affected with an EORD. Linkage analysis revealed a maximal lod score of 4.02 (theta=0.1) for the marker D1S207 on 1p31. Mutational screening of the RPE65 gene identified a homozygous R91W mutation co-segregating with the disease in all affected individuals. Eleven homozygotes had nystagmus and acuities ranging from CF to NLP. Two retinal patterns were identified: pattern 1 presented mid-peripheral deep white dot deposits and virtually no clumped pigmentation, whereas pattern 2 showed mid-peripheral pigmented clumps without any white deposits. Homozygotes had no detectable full-field ERG and an abnormal pupillary light reflex. Eleven heterozygotes had normal visual function.

CONCLUSION

We identified and characterised an endemic form of early onset rod-cone dystrophy in a consanguineous population from northeastern Tunisia, due to the prevalence of a single RPE65 mutation. Two funduscopic patterns were identified: white dot deposits in earlier stages and clumped pigment in later stages.

Towards improved clinical characterization of Leber congenital amaurosis: neurological and systemic findings

Leber congenital amaurosis (LCA) is the most severe form of inherited retinal dystrophy that presents in infancy. LCA is both clinically and genetically heterogeneous. The aim of our study was to clarify the clinical aspects of LCA and to contribute to improved characterization of the disorder. We studied 40 children affected by LCA (mean age at first observation: 19 months, range: 8-50 months), who underwent a comprehensive evaluation that included: neurophthalmological evaluation, electroretinogram (ERG), and visual evoked potentials (VEPs), general and neurological examinations, developmental assessment using scales for visually impaired children, neuroradiological examinations, hepatic and renal function and metabolic investigations, brainstem auditory evoked potentials (BAEPs), EEG, and hand radiographs. Analyses of known LCA genes are ongoing. The subjects are still being followed up at 6-/12-month intervals. All the subjects fulfilled De Laey's criteria for LCA. The neurological examination was abnormal in 31 cases (hypotonia, ataxia with/without associated cerebellar signs). Cognitive development was normal in 24 cases, borderline in five, and subnormal in 11. Mild and nonspecific alterations on MRI were present in seven cases, and "molar tooth" sign in four; all the others had a normal neuroradiological picture. Among the subjects presenting with neurological signs, a subgroup (13 patients) emerged that was characterized by systemic (skin, kidney, liver) involvement. Our data confirm that LCA is a heterogeneous entity that can present as an isolated ocular manifestation, or in association with neurological and systemic abnormalities and support the need for a multidisciplinary approach to this entity and for genotype-phenotype studies.

Advances in AAV-mediated gene transfer for the treatment of inherited disorders

The holy grail of gene therapy is the cure of genetic diseases. To achieve this goal, a vector system is desirable that offers a high level of safety combined with clinical efficacy and versatility in terms of potential applications. Gene therapy vectors based on recombinant adeno-associated viruses (AAVs) meet all of these criteria: They are nonpathogenic, devoid of viral coding sequences, and mediate long-term gene expression in the absence of an immune or inflammatory response. Moreover, with the recent discovery of novel AAV serotypes, there is now one preferred serotype for nearly every organ or tissue to target. Thus, AAV gene therapy vectors are increasingly becoming the vectors of choice for the treatment of inherited disorders.

The genetic and molecular basis of congenital eye defects

The mature eye is a complex organ that develops through a highly organized process during embryogenesis. Alterations in its genetic programming can lead to severe disorders that become apparent at birth or shortly afterwards; for example, one-half of the cases of blindness in children have a genetic cause. This review outlines the genetic basis of eye development, as determined by mutation analysis in patients and in model organisms. A better understanding of how this intricate organ develops at the genetic and cellular level is central to our understanding of the pathologies that afflict it.