Leber Congenital Amaurosis Patients Research Articles

Spectrum of NPHP6/CEP290 mutations in Leber congenital amaurosis and delineation of the associated phenotype

Leber congenital amaurosis (LCA) is the earliest and most severe retinal degeneration responsible for congenital blindness. Hitherto, 13 LCA genes have been mapped, nine of which have been identified. Recently, mutations in the NPHP6/CEP290 gene were shown to account for Joubert and Senior-Loken syndromes and to represent a frequent cause of isolated LCA. All LCA patients shared an intronic mutation resulting in an aberrantly spliced transcript and low levels of wild-type transcript that was believed to explain the absence of cerebellar and renal involvement in these patients. Here, we confirm the high frequency of NPHP6/CEP290 mutations in our series of LCA families hailing worldwide (22%). However, we show that conversely to other LCA genes, NPHP6 is involved in families of European descent only (38/38). A total of 24 different mutations were found, 23 of which are novel (one founder mutation in the North region of France). All mutations but two were either nonsense, frameshift, or splice-site changes. The common NPHP6/CEP290 intronic mutation accounted for 43% (33/76) of all disease alleles. Twelve families did not carry this common intronic mutation. At least 10 out of them harboured two mutations expected to truncate the protein questioning the relevance of the assumption according to which the retinal-restricted phenotype in LCA patient could be due to a residual NPHP6/CEP290 activity. Finally, we show that all patients were affected with the cone-rod subtype of the disease whatever their NPHP6/CEP290 genotype.

CRB1Heterozygotes with Regional Retinal Dysfunction: Implications for Genetic Testing of Leber Congenital Amaurosis

To test human CRB1 heterozygotes for possible clinical or functional retinal changes and to evaluate whether a patient with Leber congenital amaurosis (LCA) with CRB1 mutations not consistent with previously described CRB1 phenotypes carried a modifier allele in another LCA gene. Seven unrelated heterozygous carriers of CRB1 mutations underwent phenotyping by full eye examinations (indirect ophthalmoscopy and slit lamp biomicroscopy) and functional testing (standard full-field electroretinography [ERG] and multifocal ERG). For genotyping of the LCA patients and their parents, denaturing high-performance liquid chromatography (dHPLC) analyses were performed, followed by sequence analysis of CRB1, followed by sequence analysis of the AIPL1 and CRX genes to identify a putative modifier effect in a patient with an atypical CRB1 phenotype. Reduced full-field ERG b-wave amplitudes were observed with scotopic -2 dB flash (140 microV; P < 0.05), normal full-field cone ERGs, and significant regional retinal dysfunction on mfERG in five of seven carriers of CRB1 mutations. A known AIPL1 mutation (p. R302L) was identified as a potential modifier allele in a patient with LCA carrying two CRB1 mutations and with a prominent maculopathy. In human heterozygotes of CRB1 mutations (parents of offspring with LCA), distinctive regional retinal dysfunctions were found by multifocal ERG measurements that were consistent with the focal histologic abnormalities reported for the two CRB1 knockout mice models. This phenotypic finding may identify CRB1 carriers and point to the causal gene defect in affected LCA offspring, significantly facilitating the molecular diagnostic process. Evidence suggests a modifier allele in AIPL1 in a patient with LCA with prominent atrophic macular lesions and homozygous defects in CRB1.

A G1103R Mutation in CRB1 is Co-Inherited with High Hyperopia and Leber Congenital Amaurosis

Purpose: To identify the genetic basis of recessive inheritance of high hyperopia and Leber congenital amaurosis (LCA) in a family of Middle Eastern origin. Materials and methods: The patients were examined using standard ophthalmic techniques. DNA samples were obtained and genetic linkage was carried out using polymorphic markers flanking the known genes and loci for LCA. Exons were amplified and sequenced. Results: All four members of this family affected by LCA showed high to extreme hyperopia, with average spherical refractive errors ranging from +5.00 to +10.00. Linkage was obtained to 1q31.3 with a maximal LOD score of 5.20 and a mutation found in exon 9 of the CRB1 gene, causing a G1103R substitution at a highly conserved site in the protein. CRB1 is a vertebrate homolog of the Drosophila crumbs gene, which is required for photoreceptor morphogenesis, and has been associated with either retinitis pigmentosa (RP) or LCA. This sequence variant has previously been reported as a compound heterozygote in one sporadic LCA patient. Conclusion: Although hyperopia has been associated with LCA, it is typically moderate and variable between patients with the same mutation. In addition, some CRB1 mutations can be associated with either RP or LCA. We have shown that hyperopia and LCA are linked to the mutant CRB1 gene itself and are not dependent on unlinked modifiers.

Interaction of nephrocystin-4 and RPGRIP1 is disrupted by nephronophthisis or Leber congenital amaurosis-associated mutations

RPGR-interacting protein 1 (RPGRIP1) is a key component of cone and rod photoreceptor cells, where it interacts with RPGR (retinitis pigmentosa GTPase regulator). Mutations in RPGRIP1 lead to autosomal recessive congenital blindness [Leber congenital amaurosis (LCA)]. Most LCA-associated missense mutations in RPGRIP1 are located in a segment that encodes two C2 domains. Based on the C2 domain of novel protein kinase C epsilon (PKC epsilon), we built a 3D-homology model for the C-terminal C2 domain of RPGRIP1. This model revealed a potential Ca2+-binding site that was predicted to be disrupted by a missense mutation in RPGRIP1, which was previously identified in an LCA patient. Through yeast two-hybrid screening of a retinal cDNA library, we found this C2 domain to specifically bind to nephrocystin-4, encoded by NPHP4. Mutations in NPHP4 are associated with nephronophthisis and a combination of nephronophthisis and retinitis pigmentosa called Senior-Løken syndrome (SLSN). We show that RPGRIP1 and nephrocystin-4 interact strongly in vitro and in vivo, and that they colocalize in the retina, matching the panretinal localization pattern of specific RPGRIP1 isoforms. Their interaction is disrupted by either mutations in RPGRIP1, found in patients with LCA, or by mutations in NPHP4, found in patients with nephronophthisis or SLSN. Thus, we provide evidence for the involvement of this disrupted interaction in the retinal dystrophy of both SLSN and LCA patients.

Lecithin:Retinol Acyltransferase Is Responsible for Amidation of Retinylamine, a Potent Inhibitor of the Retinoid Cycle

Lecithin:retinol acyltransferase (LRAT) catalyzes the transfer of an acyl group from the sn-1 position of phosphatidylcholine to all-trans-retinol (vitamin A) and plays an essential role in the regeneration of visual chromophore as well as in the metabolism of vitamin A. Here we demonstrate that retinylamine (Ret-NH2), a potent and selective inhibitor of 11-cis-retinal biosynthesis (Golczak, M., Kuksa, V., Maeda, T., Moise, A. R., and Palczewski, K. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 8162-8167), is a substrate for LRAT. LRAT catalyzes the transfer of the acyl group onto Ret-NH2 leading to the formation of N-retinylpalmitamide, N-retinylstearamide, and N-retinylmyristamide with a ratio of 15:6:2, respectively. The presence of N-retinylamides was detected in vivo in mice supplemented with Ret-NH2. N-Retinylamides are thus the main metabolites of Ret-NH2 in the liver and the eye and can be mobilized by hydrolysis/deamidation back to Ret-NH2. Using two-photon microscopy and the intrinsic fluorescence of N-retinylamides, we showed that newly formed amides colocalize with the retinyl ester storage particles (retinosomes) in the retinal pigment epithelium. These observations provide new information concerning the substrate specificity of LRAT and explain the prolonged effect of Ret-NH2 on the rate of 11-cis-retinal recovery in vivo.

EVALUATION OF GENOTYPE–PHENOTYPE ASSOCIATIONS IN LEBER CONGENITAL AMAUROSIS

To describe the clinical phenotypes associated with various genotypes known to cause Leber congenital amaurosis (LCA). One hundred ten LCA patients were screened for various probable disease-causing gene sequence variations. Those patients with a probable disease-causing sequence variation in one of six genotypes were recalled for a follow-up examination. Evaluations included assessment of visual acuity, slit-lamp biomicroscopy, and dilated fundus examination. When possible, Goldmann perimetry was also performed. Of the 37 LCA patients with suspected disease-causing sequence variations, 7 had an AIPL1 variation, 8, a CRB1 variation, 2, a CRX variation, 4, a GUCY2D variation, 11, an RPE65 variation, and 5, an RPGRIP1 variation. Across the 6 genotypes, we observed a wide range of visual acuities from 20/40 to no light perception. The widest range of vision was noted for patients with a CRB1 or RPE65 variation. Younger patients with an AIPL1 or RPGRIP1 variation were found to have severely reduced vision. Drusenlike deposits were more selectively observed in patients with mutations in the AIPL1, CRB1, RPE65, and RPGRIP1 genes, whereas focal regions of peripheral chorioretinal atrophy were observed only in patients with AIPL1 or RPE65 variations. Neurologic, intellectual, or psychomotor developmental delay was noted in 8.1% of our cohort. There was considerable overlap of phenotypic expression in six genetic subtypes in our LCA cohort. However, phenotypic trends were noted in our patients' visual acuities and posterior segment findings within genotypes. These findings have practical value for genetic screening strategies for LCA patients based upon phenotype as well as for counseling patients on their visual prognosis.

Amaurose congénitale de Leber : le point sur l’hétérogénéité génétique, actualisation de la définition clinique

Leber congenital amaurosis (LCA) is the earliest and most severe form of all inherited retinal dystrophies, responsible for congenital blindness. Disease-associated mutations have been hitherto reported in seven genes. These genes are all expressed preferentially in the photoreceptor cells or the retinal pigment epithelium, but they are involved in strikingly different physiologic pathways, resulting in an unforeseeable pathophysiologic variety. This broad genetic and physiologic heterogeneity, which could greatly increase in the coming years, hinders molecular diagnosis in LCA patients. Genotyping is, however, required to establish genetically defined subgroups of patients ready for therapy. Here we report a comprehensive mutational analysis of all the known genes in 179 unrelated LCA patients, including 52 familial and 127 sporadic (27/127 consanguineous) cases. Mutations were identified in 47.5% of patients. GUCY2D accounted for by far the largest part of the LCA cases in our series (21.2%), followed by CRB1 (10%), RPE65 (6.1%), RPGRIP1 (4.5%), AIPL1 (3.4%), TULP1 (1.7%) and CRX (0.6%). The clinical history of all patients with mutations was carefully revisited in the search for phenotype variations. Genotype-phenotype correlations were found that made it possible to divide patients into two main groups. The first one includes patients whose symptoms fit the traditional definition of LCA, i.e., congenital or very early cone-rod dystrophy, while the second group gathers patients affected with severe yet progressive rod-cone dystrophy. In addition, objective ophthalmologic data subdivided each group into two subtypes. Based on these findings, we have drawn decisional flowcharts directing the molecular analysis of LCA genes in a given case. These flowcharts will hopefully lighten the onerous task of genotyping new patients, but only if the most precise clinical history since birth is available.

Distrofias retinianas da infância: análise retrospectiva

OBJETIVOS: Descrever o quadro clinico e os resultados dos exames complementares dos pacientes portadores das seguintes distrofias retinianas: amaurose congenita de Leber (ACL), acromatopsia, distrofia de cones e distrofia mista, atendidos no Servico de Visao Subnormal do Hospital Sao Geraldo da UFMG, no periodo de 1992 a 2003. METODOS: Analise retrospectiva dos prontuarios de 40 pacientes, sendo 10 portadores de ACL, 17 com acromatopsia, 6 com distrofia de cones e 7 com distrofia mista. RESULTADOS: A acuidade visual foi extremamente baixa na ACL, variando de 20/710 a percepcao luminosa. Situou-se em torno de 20/200 na acromatopsia, 20/280 na distrofia de cones e 20/260 na mista. A alta hipermetropia foi o erro refracional mais comum na ACL, ao passo que a hipermetropia predominou na acromatopsia e na distrofia de cones e a miopia na mista. A fundoscopia mostrou-se alterada na maioria dos casos de ACL, distrofia de cones e distrofia mista e normal na maioria dos acromatas. A compressao oculo-digital e o enoftalmo foram exclusivos da ACL, ao passo que a fotofobia e a dificuldade na discriminacao de cores predominaram nos outros grupos. O nistagmo e o estrabismo foram frequentes em todos eles. O atraso no desenvolvimento neuro-psico-motor foi muito frequente no grupo da ACL e quase ausente nos demais. A ACL apareceu associada a sindromes geneticas em 2 casos. Os sintomas da ACL e da acromatopsia se manifestaram ao nascimento ou no 1o ano de vida, ao passo que na distrofia de cones e na mista surgiram tambem em idades mais avancadas, porem nao depois dos 10 anos. A consanguinidade e a historia familiar positiva foram altamente prevalentes em todos os grupos. O ERG mostrou ausencia de resposta na ACL, reducao da resposta fotopica na acromatopsia e na distrofia de cones e reducao difusa na mista. Os testes de visao de cores mostraram alteracoes principalmente na acromatopsia e na distrofia de cones. CONCLUSOES: As distrofias retinianas da infância sao um grupo heterogeneo de doencas que se manifestam por meio de sintomas inespecificos. Uma analise cuidadosa dos sintomas, o exame oftalmologico completo e os exames complementares, principalmente ERG, testes de visao de cores e campo visual, podem ser uteis em seu diagnostico.

Retinal degeneration in Aipl1-deficient mice: a new genetic model of Leber congenital amaurosis

Leber congenital amaurosis (LCA) is the most severe inherited retinopathy, with the earliest age of onset. Because this currently incurable disease is present from birth and is a relatively rare disorder, the development of animal models that closely resemble the phenotype in patients is especially important. Our previous genetic analyses of LCA patients identified mutations in the aryl-hydrocarbon interacting protein-like 1 ( AIPL1) gene. Here we present development of an animal model of AIPL1-associated LCA, the Aipl1-deficient mouse. Aipl1 is expressed at low levels throughout human and mouse retinal development and is rapidly upregulated as photoreceptors differentiate. The mouse displays rapid retinal degeneration and massive Müller cell gliosis, resembling the phenotype of the rd mouse, which is caused by a mutation in the gene for the β-subunit of the rod-specific phosphodiesterase. We confirm that this phenotype is consistent with the human disease using electroretinograms, and document the disease pathogenesis by analyzing the development of all retinal cell types and synaptogenesis during retinal histogenesis. Ectopic expression of AIPL1 led to deregulated retinal progenitor cell proliferation and alterations in cell fate specification; however, no gross abnormalities of proliferation during retinal development were detected. Data from analysis of proliferation and cell fate specification during retinal development of Aipl1-deficient mice suggests that there may be redundancy or compensation for Aipl1 loss by other related proteins. Because this mouse model closely mimics the human retinopathy caused by homozygous mutations in this gene, it provides a preclinical model for testing therapies to rescue the vision of children whose blindness is caused by AIPL1 mutations.

Fundus autofluorescence in patients with leber congenital amaurosis.

Fundus autofluorescence (FAF), as an index of lipofuscin accumulation in the retinal pigment epithelium (RPE), provides indirect information on the level of metabolic activity of the RPE and thus the integrity of the RPE/photoreceptor complex. To investigate whether the photoreceptor/RPE complex is still viable in patients with Leber congenital amaurosis (LCA), FAF imaging was performed. Three patients with LCA (patients A, B, and C; ages, 24, 15, and 37 years, respectively) were enrolled and one patient with RP with preserved visual acuity (age, 28 years) was included as a control. The diagnosis was based on history, visual function, and Ganzfeld electroretinography (International Society for Clinical Electrophysiology of Vision [ISCEV] standard). FAF was recorded with a confocal scanning laser ophthalmoscope (cSLO; Heidelberg Retina Angiograph; Heidelberg Engineering, Heidelberg, Germany). All patients with LCA had vision reduced to perception of light and had undetectable ERGs. FAF was normal in patient A. In patient B, there was a parafoveal ring of mildly increased FAF. The midperiphery showed mildly decreased FAF. Patient C showed a parafoveal ring of moderately increased FAF. FAF was moderately decreased along the arcades and the midperiphery. The patient with RP showed a parafoveal ring of moderately increased FAF and severely decreased FAF eccentric to the macula including the periphery. The FAF findings in these patients with LCA suggest that there is continuous metabolic demand from the photoreceptors and that the RPE/photoreceptor complex is, at least in part, anatomically intact, but the photoreceptors have lost function. These findings may have implications for future treatment. It is notable that more than 20 years of severe visual impairment associated with LCA can be associated with normal FAF, indicating that photoreceptor function may be rescuable.

Leber congenital amaurosis: comprehensive survey of the genetic heterogeneity, refinement of the clinical definition, and genotype-phenotype correlations as a strategy for molecular diagnosis.

Leber congenital amaurosis (LCA) is the earliest and most severe form of all inherited retinal dystrophies, responsible for congenital blindness. Disease-associated mutations have been hitherto reported in seven genes. These genes are all expressed preferentially in the photoreceptor cells or the retinal pigment epithelium but they are involved in strikingly different physiologic pathways resulting in an unforeseeable physiopathologic variety. This wide genetic and physiologic heterogeneity that could largely increase in the coming years, hinders the molecular diagnosis in LCA patients. The genotyping is, however, required to establish genetically defined subgroups of patients ready for therapy. Here, we report a comprehensive mutational analysis of the all known genes in 179 unrelated LCA patients, including 52 familial and 127 sporadic (27/127 consanguineous) cases. Mutations were identified in 47.5% patients. GUCY2D appeared to account for most LCA cases of our series (21.2%), followed by CRB1 (10%), RPE65 (6.1%), RPGRIP1 (4.5%), AIPL1 (3.4%), TULP1 (1.7%), and CRX (0.6%). The clinical history of all patients with mutations was carefully revisited to search for phenotype variations. Sound genotype-phenotype correlations were found that allowed us to divide patients into two main groups. The first one includes patients whose symptoms fit the traditional definition of LCA, i.e., congenital or very early cone-rod dystrophy, while the second group gathers patients affected with severe yet progressive rod-cone dystrophy. Besides, objective ophthalmologic data allowed us to subdivide each group into two subtypes. Based on these findings, we have drawn decisional flowcharts directing the molecular analysis of LCA genes in a given case. These flowcharts will hopefully lighten the heavy task of genotyping new patients but only if one has access to the most precise clinical history since birth.

Clinicopathologic effects of mutant GUCY2D in Leber congenital amaurosis

Purpose To study the retinal degeneration in an 11 1 2 -year-old patient with Leber congenital amaurosis (LCA) caused by mutation in GUCY2D. Study design Comparative human tissue study. Participants Two subjects with LCA; postmortem eye from one LCA patient and three normal donors. Methods Clinical and visual function studies were performed between the ages of 6 and 10 years in the LCA eye donor and at age 6 in an affected sibling. Genomic DNA was screened for mutations in known LCA genes. The retina of the 11 1 2 -year-old subject with LCA was compared with normal retinas from donors age 3 days, 18 years, and 53 years. The tissues were processed for histopathologic studies and immunofluorescence with retinal cell-specific antibodies. Results Vision in both siblings at the ages examined was limited to severely impaired cone function. Mutation in the GUCY2D gene was identified in both siblings. Histopathologic study revealed rods and cones without outer segments in the macula and far periphery. The cones formed a monolayer of cell bodies, but the rods were clustered and had sprouted neurites in the periphery. Rods and cones were not identified in the midperipheral retina. The inner nuclear layer appeared normal in thickness throughout the retina, but ganglion cells were reduced in number. Conclusions An 11 1 2 -year-old subject with LCA caused by mutant GUCY2D had only light perception but retained substantial numbers of cones and rods in the macula and far periphery. The finding of numerous photoreceptors at this age may portend well for therapies designed to restore vision at the photoreceptor level.

One of the genes for Leber congenital amaurosis, AIPL-1, is associated with a cell cycle regulatory protein

There are currently six genes associated with Leber congenital amaurosis (LCA), the congenital form of retinitis pigmentosa (RP). Studying LCA has led to an increased understanding of normal and aberrant retinal development. Identifying genes for blindness and hereditary eye diseases is important for ophthalmologists as it improves our understanding of the disease mechanisms, improves our diagnostic and prognostic abilities, and provides a potential target for future therapy. Before treatment trials, it is imperative to study gene function. Akey et al. 1 explored the function of AIPL-1, aryl hydrocarbon receptorinteracting protein-like-1, one of the genes associated with LCA. LCA patients with mutations in AIPL-1 have a particularly severe phenotype, often with light perception or hand motion vision, cataracts, keratoconus, a maculopathy, and severe retinal pigment degeneration. Sequence analysis and comparisons with other proteins suggest that AIPL-1 may be important in protein trafficking, folding, and/or stabilization. The new studies by Akey and colleagues show that AIPL-1 is present in developing photoreceptors, and in adult photoreceptors. They also showed that AIPL-1 protein is associated with a protein that controls cell-cycle progression, called NUB-1. Using a yeast 2 hybrid system, they screened a bovine retinal cDNA library and found that AIPL-1 interacts with NUB-1. They then studied the consequences of introducing mutations into AIPL-1 on AIPL-1 NUB-1 protein-protein interactions. The AIPL-1 mutations were from blind infants with LCA and were artificially constructed and introduced into an expression system. The majority of mutations significantly reduced the interactions between the two proteins, providing evidence that the interactions are important and real. They then performed Western blot analysis on retinoblastoma Y79 cells and found both NUB-1 and AIPL-1 bands. Retinoblastoma has been shown by others to resemble retinal progenitor cells. In-situ hybridization of embryonic and postnatal mouse retina showed expression of both NUB-1 and AIPL-1 in the photoreceptors, especially the inner segment. The experiments by Akey and co-worders strongly suggest that AIPL-1 is expressed in retinal progenitor cells and is associated with a

The inherited blindness associated protein AIPL1 interacts with the cell cycle regulator protein NUB1.

Mutations in the aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1) gene have been found in patients with Leber congenital amaurosis (LCA), a severe, early-onset form of retinal degeneration. To determine the normal function of AIPL1 and to better understand how mutations in this gene cause disease, we performed a yeast two-hybrid screen to identify AIPL1-interacting proteins in the retina. One of the identified interacting proteins corresponds to NUB1 (NEDD8 Ultimate Buster 1), which is thought to control many biological events, especially cell cycle progression, by downregulating NEDD8 expression. The AIPL1-NUB1 interaction was verified by co-immunoprecipitation studies in Y79 retinoblastoma cells, demonstrating that this interaction occurs within cells that share a number of features with retinal progenitor cells. Furthermore, we examined the localization of the AIPL1 protein within developing and adult retinas, and found that AIPL1 is present in the developing photoreceptor layer of the human retina and within the photoreceptors of the adult retina. Similar to AIPL1, NUB1 is also expressed in the developing and adult retina. Therefore, it is possible that the early-onset form of retinal degeneration seen in LCA patients with AIPL1 mutations may be due to a defect in the regulation of cell cycle progression during photoreceptor maturation. These data raise the possibility that AIPL1 is important for appropriate photoreceptor formation during development and/or survival following differentiation.

Evidence of a founder effect for the RETGC1 (GUCY2D) 2943DelG mutation in Leber congenital amaurosis pedigrees of Finnish origin.

Leber congenital amaurosis (LCA) is the earliest and most severe form of all inherited retinal dystrophies. It is a genetically heterogeneous condition as six disease-causing genes have been hitherto identified. Among them, RETGC1 (GUCY2D), is more frequently implicated in our series of LCA patients. Interestingly, 70 % of the families with RETGC1 mutations are originating from Mediterranean countries, the remaining families (30%) being originating from various countries across the world. Here, we report, the identification of the same homozygous RETGC1 nonsense mutation in three unrelated and non-consanguineous LCA families of Finnish origin, suggesting a founder effect. Interestingly, no linkage desequilibrium was found using polymorphic markers flanking the RETGC1 gene, supporting the view that the mutation is very ancient. Haplotype studies and Bayesian calculation point the founder mutation to 150 generations (95% credible interval 80-240 generations), i.e., 3000 years ago.

Molecular genetics of Leber congenital amaurosis.

Leber congenital amaurosis (LCA) is the most common inherited cause of blindness in childhood and is characterised by a severe retinal dystrophy before the age of one year. Six genes have been identified that together account for approximately half of all LCA patients. These genes are expressed preferentially in the retina or the retinal pigment epithelium. Their putative functions are quite diverse and include retinal embryonic development (CRX), photoreceptor cell structure (CRB1), phototransduction (GUCY2D), protein trafficking (AIPL1, RPGRIP1), and vitamin A metabolism (RPE65). The molecular data for CRB1 and RPE65 support previous hypotheses that LCA can represent the severe end of a spectrum of retinal dystrophies. Given the diverse mechanisms underlying the disease, future therapies of LCA may need to be tailored to certain genetically defined subgroups. Based on experimental evidence in mice and dogs, patients with disturbed retinal metabolism of vitamin A through a mutation in the RPE65 gene will likely be the first candidates for future therapeutic trials.

RPE65 gene: multiplex PCR and mutation screening in patients from India with retinal degenerative diseases.

We used multiplex PCR follwed by sequencing to screen for mutations in the 14 exons of the RPE65 gene in early-childhood-onset autosomal recessive retinitis pigmentosa (arRP) and Leber's congenital amaurosis (LCA) patients. The RPE65 protein is believed to play an important role in the metabolism of vitamin A in the visual cycle and mutations identified in the gene could have implications for vitamin A-based therapeutic intervention. We were able to identify a homozygous mutation (AAT --> AAG) in exon 9 in an arRP patient and a heterozygous missense transversion (AAT --> AAG) also in exon 9 of an LCA patient. We also identified a polymorphism in exon 10 (GAG --> GAA) in an arRP as well as an LCA patient. Mutation screening would be greatly facilitated by multiplex PCR which could cut down costs, labour and time involved. The nucleotide changes observed in this study could be de novo. Though a larger study has been undertaken, from the preliminary results it appears that in India the RPE65 gene seems to be less involved in causation of LCA.

Visual improvement in Leber congenital amaurosis and the CRX genotype

Purpose: In order to determine genotype-phenotype correlations in Leber congenital amaurosis (LCA), we analyzed the phenotype and genotype of 250 LCA children. We identified a heterozygous CRX mutation in an affected mother and son, and describe the ocular phenotype of the proband from birth through infancy to age 11 years. Methods: Best-corrected Snellen visual acuities, electroretinograms (ERGs), and Goldmann visual fields were measured, while SSCP and direct sequencing were done for genotyping. Results: The proband had congenital nystagmus, amaurotic, paradoxical pupils, and arteriolar narrowing, without a pigmentary retinopathy. The child had very poor fixation and wandering nystagmus at age 5 months, but had measurable vision at age 6 years. Snellen visual acuities were 20/900 at that time, and slowly improved to 20/150 by age 11 years. Perimetry revealed 60° fields with the V4e target at ages 9 and 10 years, with a new 20° inferior island to the III4e target. ERGs at 5 and 8 months were non-detectable, while the photopic ERGs at age 10 years and again at 11 years showed measurable cone a- and b-waves. At age 47, the phenotype of the affected mother consisted of hand motion vision, a pigmentary retinopathy, and non-detectable visual fields and ERGs. We identified a heterozygous CRX mutation, A177?1bp (529delG), in both affected individuals, which is predicted to cause a frameshift and introduces a premature termination codon at position 186. Conclusions: We report a CRX genotype with an ocular phenotype that consists of spontaneous, marked visual improvement in the proband from birth to age 11 years, which is unlike the previous six reports of LCA patients with the CRX genotype.

Complete exon-intron structure of the RPGR-interacting protein (RPGRIP1) gene allows the identification of mutations underlying Leber congenital amaurosis.

Leber congenital amaurosis (LCA) is a genetically heterogeneous autosomal recessive condition responsible for congenital blindness or greatly impaired vision since birth. So far, six LCA loci have been mapped but only 4 out of 6 genes have been identified. A genome-wide screen for homozygosity was conducted in seven consanguineous families unlinked to any of the six LCA loci. Evidence for homozygosity was found in two of these seven families at the 14q11 chromosomal region. Two retinal specific candidate genes were known to map to this region, namely the neural retina leucine zipper (NRL) and the retinitis pigmentosa GTPase regulator interacting protein (RPGRIP1). No mutation of the NRL gene was found in any of the two families. Thus, we determined the complete exon-intron structure of the RPGRIP1 gene. RPGRIP1 encompasses 24 coding exons, nine of which are first described here with their corresponding exon-intron boundaries. The screening of the gene in the two families consistent with linkage to chromosome 14q11 allowed the identification of a homozygous null mutation and a homozygous missense mutation, respectively. Further screening of LCA patients unlinked to any of the four already identified LCA genes (n=86) identified seven additional mutations in six of them. In total, eight distinct mutations (5 out of 8 truncating) in 8/93 patients were found. So far this gene accounts for eight out of 142 LCA cases in our series (5.6%).

Leber congenital amaurosis caused by a homozygous mutation (R90W) in the homeodomain of the retinal transcription factor CRX: direct evidence for the involvement of CRX in the development of photoreceptor function.

The CRX (cone-rod homeobox) gene is specifically expressed in developing and mature photoreceptors and encodes an otd/Otx-like paired homeodomain protein. Mutant alleles of the CRX gene have recently been associated with autosomal dominant cone-rod dystrophy (CORD) as well as dominant Leber congenital amaurosis (LCA). Since LCA is more commonly inherited in an autosomal recessive manner, we examined a cohort of recessive LCA patients for CRX mutations. A homozygous substitution of arginine (R) at codon 90 by tryptophan (W) was identified in the CRX homeodomain of one of the probands who was nearly blind from birth. A group of 48 control individuals and 190 previously characterized CORD probands did not reveal this sequence change. The mutant CRXR90W homeodomain demonstrated decreased binding to the previously identified cis sequence elements in the rhodopsin promoter. In transient transfection experiments, the mutant protein showed significantly reduced ability to transactivate the rhodopsin promoter, as well as lower synergistic activation with the bZIP transcription factor NRL. Heterozygosity of the mutant CRX (R90W) allele was detected in both parents and in an older sibling. Ophthalmologic examination and electro-retinography revealed a subtle abnormality of cone function in both the parents. These data suggest that the R90W mutation results in a CRX protein with reduced DNA binding and transcriptional regulatory activity and that the subsequent changes in photoreceptor gene expression lead to the very early onset severe visual impairment in LCA.