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

Sensitive period for the plasticity of alpha activity in humans

Visual experience is crucial for the development of neural processing. For example, alpha activity development is a vision-dependent mechanism. Indeed, studies report no alpha activity is present in blind adults. Nevertheless, studies have not investigated the developmental trajectory of this activity in infants and children with blindness. Here, we hypothesize that the difference in neural activity of blind compared to sighted subjects is: absent at birth, progressive with age, specifically occipital and linked to a gradual motor impairment. Therefore, we consider spectral power of resting-state EEG and its association with motor impairment indices, in blind subjects and in sighted controls between 0 and 11 years of age. Blind subjects show posterior alpha activity during the first three years of life, although weaker and slower maturing compared to sighted subjects. The first great differentiation between blind and sighted subjects occurs between 3 and 6 years of age. Starting in this period, reduced alpha activity increases the probability of motor impairment in blind subjects, likely because of impaired perception/interaction. These results show that visual experience mediates the neural mechanisms generating alpha oscillations during the first years of life, suggesting that it is a sensitive period for the plasticity of this process.

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.

Glial and neuronal expression of the Inward Rectifying Potassium Channel Kir7.1 in the adult mouse brain

Inward Rectifying Potassium channels (Kir) are a large family of ion channels that play key roles in ion homeostasis and neuronal excitability. The most recently described Kir subtype is Kir7.1, which is known as a K⁺ transporting subtype. Earlier studies localised Kir7.1 to subpopulations of neurones in the brain. However, the pattern of Kir7.1 expression across the brain has not previously been examined. Here, we have determined neuronal and glial expression of Kir7.1 in the adult mouse brain, using immunohistochemistry and transgenic mouse lines expressing reporters specific for astrocytes [glial fibrillary acidic protein‐enhanced green fluorescent protein (GFAP‐EGFP], myelinating oligodendrocytes (PLP‐DsRed), oligodendrocyte progenitor cells (OPC, Pdgfra‐creER^T2/Rosa26‐YFP double‐transgenic mice) and all oligodendrocyte lineage cells (SOX10‐EGFP). The results demonstrate significant neuronal Kir7.1 immunostaining in the cortex, hippocampus, cerebellum and pons, as well as the striatum and hypothalamus. In addition, astrocytes are shown to be immunopositive for Kir7.1 throughout grey and white matter, with dense immunostaining on cell somata, primary processes and perivascular end‐feet. Immunostaining for Kir7.1 was observed in oligodendrocytes, myelin and OPCs throughout the brain, although immunostaining was heterogeneous. Neuronal and glial expression of Kir7.1 is confirmed using neurone‐glial cortical cultures and optic nerve glial cultures. Notably, Kir7.1 have been shown to regulate the excitability of thalamic neurones and our results indicate this may be a widespread function of Kir7.1 in neurones throughout the brain. Moreover, based on the function of Kir7.1 in multiple transporting epithelia, Kir7.1 are likely to play an equivalent role in the primary glial function of K⁺ homeostasis. Our results indicate Kir7.1 are far more pervasive in the brain than previously recognised and have potential importance in regulating neuronal and glial function.

Identification of a mutation in CNNM4 by whole exome sequencing in an Amish family and functional link between CNNM4 and IQCB1

We investigated an Amish family in which three siblings presented with an early-onset childhood retinal dystrophy inherited in an autosomal recessive fashion. Genome-wide linkage analysis identified significant linkage to marker D2S2216 on 2q11 with a two-point LOD score of 1.95 and a multi-point LOD score of 3.76. Whole exome sequencing was then performed for the three affected individuals and identified a homozygous nonsense mutation (c.C1813T, p.R605X) in the cyclin and CBS domain divalent metal cation transport mediator 4 (CNNM4) gene located within the 2p14-2q14 Jalili syndrome locus. The initial assessment and collection of the family were performed before the clinical delineation of Jalili syndrome. Another assessment was made after the discovery of the responsible gene and the dental abnormalities characteristic of Jalili syndrome were retrospectively identified. The p.R605X mutation represents the first probable founder mutation of Jalili syndrome identified in the Amish community. The molecular mechanism underlying Jalili syndrome is unknown. Here we show that CNNM4 interacts with IQCB1, which causes Leber congenital amaurosis (LCA) when mutated. A truncated CNNM4 protein starting at R605 significantly increased the rate of apoptosis, and significantly increased the interaction between CNNM4 and IQCB1. Mutation p.R605X may cause Jalili syndrome by a nonsense-mediated decay mechanism, affecting the function of IQCB1 and apoptosis, or both. Our data, for the first time, functionally link Jalili syndrome gene CNNM4 to LCA gene IQCB1, providing important insights into the molecular pathogenic mechanism of retinal dystrophy in Jalili syndrome.

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.

Septo-optic dysplasia in childhood: the neurological, cognitive and neuro-ophthalmological perspective

AIM

We set out to describe 17 patients with septo-optic dysplasia (SOD), focusing on the little-explored neurological, cognitive, and neuro-ophthalmological components. A further aim was to identify possible clinical correlations and phenotypic characteristics within the diagnostic spectrum.

METHOD

We collected clinical-instrumental data (from the history, general and neurological examination, developmental assessment, and neuro-ophthalmological, neuroradiological, neurophysiological, and endocrinological evaluations) on nine males and eight females (mean age 34.4mo, SD 31.6; range 4mo-9y 6mo) diagnosed with SOD who were referred to our Centre of Child Neuro-ophthalmology between 1999 and 2010.

RESULTS

We observed a heterogeneous clinical spectrum characterized by nervous system, visual, and endocrine dysfunctions; optic nerve involvement was present in all 17 children, midline brain defects in 14, and cortical developmental malformations in seven. Developmental/cognitive delay and relational and communication difficulties were observed in eight and seven children, respectively, and reduced visual acuity and oculomotor dysfunction were observed in all. Pituitary hormone deficiencies were present in nine children.

INTERPRETATION

Nervous system involvement emerged as a key feature of SOD. As part of a holistic approach to the disease, particular attention should be paid to this aspect. The emergence of new clinical correlations and correlations between clinical features and three SOD subtypes opens the way for better clarification of this disease and, therefore, more targeted diagnosis, follow-up, and care of affected children.

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.

Brain imaging studies in Leber's congenital amaurosis: new radiologic findings associated with the complex trait

Purpose

To report the incidence and new findings of abnormal brain imaging studies associated with patients initially diagnosed with Leber's congenital amaurosis (LCA) without definite systemic abnormalities and to determine the need for brain imaging studies in these patients.

Methods

A retrospective review of medical records was performed in 83 patients initially diagnosed as LCA and without definite systemic abnormalities before the age of 6 months in 2 tertiary referral centers. Brain magnetic resonance imaging was performed in 31 of 83 patients (37.3%).

Results

Six of 31 patients (19%) had radiologically documented brain abnormalities. Two patients had cerebellar vermis hypoplasia, 1 patient showed an absence of septum pellucidum, 2 subjects showed mild external hydrocephalus, and 1 patient was found to have a small cerebellum.

Conclusions

Approximately one fifth of the LCA patients in whom brain imaging was performed were associated with brain abnormalities, including the absence of septum pellucidum, which has not been documented in the literature. Brain imaging is mandatory in patients primarily diagnosed with LCA, even without definite neurologic or systemic abnormalities.

Lumpers or Splitters? The Role of Molecular Diagnosis in Leber Congenital Amaurosis

Clarification and classification of the congenital form of blindness known as Leber congenital amaurosis (LCA) continues to provide its challenges and dilemmas. Until recently, seven genes have been identified that cause LCA. Clarifying the relation between LCA and associated neurological abnormalities such as autism, seizures, and hypotony, and unraveling the relationship between the ocular LCA phenotype and that associated with distinct systemic entities such as Joubert syndrome, Senior-Loken syndrome and Saldino-Mainzer syndrome has taken on new importance with the discovery that a substantial proportion of patients with LCA have mutations in the CEP290 gene that causes Joubert syndrome. This commentary explores the implications of this recent discovery and revisits the classification of LCA.

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.

Physiological Role of Retinyl Palmitate in the Skin

The skin is similar to other organs in how it absorbs, stores, and metabolizes vitamin A. However, because of the anatomical location of skin and the specialized physiological roles it plays, there are ways in which the skin is rather unique. The stratified structure of the epidermis results from the orchestration of retinoid-influenced cellular division and differentiation. Similarly, many of the physiological responses of the skin, such as dermal aging, immune defense, and wound healing, are significantly affected by retinoids. While much is known about the molecular events through which retinoids affect the skin's responses, more remains to be learned. Interest in the effects of retinol, retinyl palmitate, and other retinoids on the skin, fueled in part by the promise of improved dermatologic and cosmetic products, will undoubtedly make the effects of retinoids on skin a subject for continued intense investigation.

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.