Two novel CRX mutant proteins causing autosomal dominant Leber congenital amaurosis interact differently with NRL

Leber congenital amaurosis (LCA) is a congenital retinal dystrophy characterized by severe visual loss in infancy and nystagmus. Although most often inherited in an autosomal recessive fashion, rare individuals with mutations in the cone-rod homeobox gene, CRX, have dominant disease. CRX is critical for photoreceptor development and acts synergistically with the leucine-zipper transcription factor, NRL. We report on the phenotype of two individuals with LCA due to novel, de novo CRX mutations, c.G264T(p.K74N) and c.413delT(p.I138fs48), that reduce transactivation in vitro to 10% and 30% of control values, respectively. Whereas the c.413delT(p.I138fs48) mutant allows co-expressed NRL to transactivate independently at its normal, baseline level, the c.G264T(p.K74N) mutant reduces co-expressed NRL transactivation and reduces steady state levels of both proteins. Although both mutant proteins predominantly localize normally to the nucleus, they also both show variable cytoplasmic localization. These observations suggest that some CRX-mediated LCA may result from effects beyond haploinsufficiency, such as the mutant protein interefering with other transcription factors' function. Such patients would therefore not likely benefit from a simple, gene-replacement strategy for their disease.

Deducing the pathogenic contribution of recessive ABCA4 alleles in an outbred population

Accurate prediction of the pathogenic effects of specific genotypes is important for the design and execution of clinical trials as well as for meaningful counseling of individual patients. However, for many autosomal recessive diseases, it can be difficult to deduce the relative pathogenic contribution of individual alleles because relatively few affected individuals share the same two disease-causing variations. In this study, we used multiple regression analysis to estimate the pathogenicity of specific alleles of ABCA4 in patients with retinal phenotypes ranging from Stargardt disease to retinitis pigmentosa. This analysis revealed quantitative allelic effects on two aspects of the visual phenotype, visual acuity (P < 10⁻³) and visual field (P < 10⁻⁷). Discordance between visual acuity and visual field in individual patients suggests the existence of at least two non-ABCA4 modifying factors. The findings of this study will facilitate the discovery of factors that modify ABCA4 disease and will also aid in the optimal selection of subjects for clinical trials of new therapies.

T-cell infiltration in autosomal dominant neovascular inflammatory vitreoretinopathy

PURPOSE

Autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV) is a familial blinding disease of unknown pathophysiology. The eyes and sera from patients with ADNIV were studied to understand the immune response in this condition.

METHODS

The clinical case of an ADNIV patient was reviewed. Eye specimens from two donors with ADNIV were examined with a panel of standard histopathological stains and immunohistochemical markers. These findings were compared to specimens of noninflammatory eye disease. Sera from twelve patients were also tested against retinal protein western blots for the presence of autoretinal antibodies.

RESULTS

Each of the ADNIV and control eyes showed degenerative features of phthisis bulbi. Immunohistological stains revealed a supraciliary T-cell infiltrate in ADNIV eyes composed of cluster of differentiation-4 (CD4) positive and cluster of differentiation-8 (CD8)-positive cells. No immunoglobulin or B cells were detected in these eyes. Inflammatory cells were absent from the control eyes. No specific autoretinal antibodies were detected in ADNIV sera.

CONCLUSIONS

Aberrant T-cell-mediated processes may underlie ADNIV, and therapeutics directed at T cells may better manage inflammation in these patients. Genes related to T-cell function are high priority screening candidates.

Complement component C5a activates ICAM-1 expression on human choroidal endothelial cells

PURPOSE

The complement system plays a crucial role in the progression of age-related macular degeneration (AMD). In this study, the authors sought to evaluate the pathophysiologic roles of complement components C3a and C5a in the human choroid in AMD.

METHODS

Human RPE/choroid was assayed for the presence of C3a and C5a receptors (C3aR and C5aR) using RT-PCR and immunohistochemistry. Choroidal endothelial cell migration and proliferation were evaluated in the presence of C5a. Organ cultures of human choroid were incubated in C5a or bovine serum albumin (BSA) followed by quantitative immunohistochemistry and quantitative PCR for ICAM-1. AMD patients and controls were genotyped at SNPs in the C5R1 and C3AR1 genes.

RESULTS

C5aR, but not C3aR, was detected in human choroid. C5a did not promote endothelial cell migration or proliferation. However, choriocapillaris endothelial cells in organ culture responded to C5a by increasing ICAM-1 mRNA and protein. No significant association of SNP genotypes was detected in AMD patients at the C3AR1 and C5R1 genes.

CONCLUSIONS

The generation of C5a peptides may lead to activation of choriocapillaris endothelial cells in AMD. Activation of the choroidal endothelium may affect the progression of AMD by recruitment of monocytes, leading to additional sequelae of AMD pathogenesis.

Discovery and functional analysis of a retinitis pigmentosa gene, C2ORF71

Retinitis pigmentosa is a genetically heterogeneous group of inherited ocular disorders characterized by progressive photoreceptor cell loss, night blindness, constriction of the visual field, and progressive visual disability. Homozygosity mapping and gene expression studies identified a 2 exon gene, C2ORF71. The encoded protein has no homologs and is highly expressed in the eye, where it is specifically expressed in photoreceptor cells. Two mutations were found in C2ORF71 in human RP patients: A nonsense mutation (p.W253X) in the first exon is likely to be a null allele; the second, a missense mutation (p.I201F) within a highly conserved region of the protein, leads to proteosomal degradation. Bioinformatic and functional studies identified and validated sites of lipid modification within the first three amino acids of the C2ORF71 protein. Using morpholino oligonucleotides to knockdown c2orf71 expression in zebrafish results in visual defects, confirming that C2ORF71 plays an important role in the development of normal vision. Finally, localization of C2ORF71 to primary cilia in cultured cells suggests that the protein is likely to localize to the connecting cilium or outer segment of photoreceptor cells.

Identification and functional analysis of the vision-specific BBS3 (ARL6) long isoform

Bardet-Biedl Syndrome (BBS) is a heterogeneous syndromic form of retinal degeneration. We have identified a novel transcript of a known BBS gene, BBS3 (ARL6), which includes an additional exon. This transcript, BBS3L, is evolutionally conserved and is expressed predominantly in the eye, suggesting a specialized role in vision. Using antisense oligonucleotide knockdown in zebrafish, we previously demonstrated that bbs3 knockdown results in the cardinal features of BBS in zebrafish, including defects to the ciliated Kupffer's Vesicle and delayed retrograde melanosome transport. Unlike bbs3, knockdown of bbs3L does not result in Kupffer's Vesicle or melanosome transport defects, rather its knockdown leads to impaired visual function and mislocalization of the photopigment green cone opsin. Moreover, BBS3L RNA, but not BBS3 RNA, is sufficient to rescue both the vision defect as well as green opsin localization in the zebrafish retina. In order to demonstrate a role for Bbs3L function in the mammalian eye, we generated a Bbs3L-null mouse that presents with disruption of the normal photoreceptor architecture. Bbs3L-null mice lack key features of previously published Bbs-null mice, including obesity. These data demonstrate that the BBS3L transcript is required for proper retinal function and organization.

Retinitis pigmentosa (RP), a disorder of retinal degeneration resulting in blindness, occurs due to mutations in dozens of different genes encoding proteins with highly diverse functions. To date, there are no effective therapies to delay or arrest retinal degeneration. RP places a large burden on affected families and on society as a whole. We have studied a syndromic form of RP known as Bardet-Biedl Syndrome (BBS), which leads to degeneration of the photoreceptor cells and is associated with non-vision abnormalities including obesity, hypertension, diabetes, and congenital abnormalities of the kidney, heart, and limbs. In this study we utilized two model systems, the zebrafish and mouse, to evaluate the function of a specific form of BBS (BBS3). We have identified a novel protein product of the BBS3 gene and demonstrated that functional and structural abnormalities of the eye occur when this form of BBS3 is absent. This finding is of significance because it indicates that BBS3 mutations can lead to non-syndromic blindness, as well as blindness associated with other clinical features. This work also indicates that treatment of BBS3 blindness will require replacement of a specific form of the BBS3 gene.

Retinal vascular abnormalities and dragged maculae in a carrier with a new NDP mutation (c.268delC) that caused severe Norrie disease in the proband

Norrie disease (ND) is caused by mutations in the ND pseudoglioma (NDP) gene (MIM 300658) located at chromosome Xp11.4-p11.3. ND is characterized by abnormal retinal vascular development and vitreoretinal disorganization presenting at birth. Systemic manifestations include sensorineural deafness, progressive mental disorder, behavioral and psychological problems, growth failure, and seizures. Other vitreoretinopathies that are associated with NDP gene mutations include X-linked familial exudative vitreoretinopathy, Coats disease, persistent fetal vasculature, and retinopathy of prematurity. Phenotypic variability associated with NDP gene mutations has been well documented in affected male patients. However, there are limited data on signs in female carriers, with mild peripheral retinal abnormalities reported in both carrier and noncarrier females of families with NDP gene mutations. Here, we report a family harboring a single base-pair deletion, c.268delC, in the NDP gene causing a severe ND phenotype in the male proband and peripheral retinal vascular abnormalities with dragged maculae similar to those observed in familial exudative vitreoretinopathy in his carrier mother.

Visual acuity in patients with Leber's congenital amaurosis and early childhood-onset retinitis pigmentosa

PURPOSE

To correlate visual acuity of patients with Leber's congenital amaurosis (LCA) and early childhood-onset retinitis pigmentosa (RP) with mutations in underlying LCA genes.

DESIGN

Multicentered retrospective observational study.

PARTICIPANTS

After exclusion of 28 subjects, 169 patients with the diagnosis of LCA and 27 patients with early childhood-onset RP were included in the study because the underlying mutations in AIPL1, GUCY2D, RDH12, RPE65, CRX, CRB1, RPGRIP1, CEP290, LCA5, and TULP1 genes could be identified in this cohort of patients.

METHODS

We collected data on best-corrected visual acuity as recorded at the time of the patient's most recent visit to one of the participating ophthalmology departments. The median and range of visual acuities for each genetic subtype were calculated separately for the LCA and early childhood-onset RP groups.

MAIN OUTCOME MEASURES

The range and median best-corrected visual acuities for each genetic subtype and age-related mean visual acuities for each genetic subtype.

RESULTS

A wide variation in visual acuity was observed in patients with LCA and RPE65, RDH12, and CRB1 mutations, whereas AIPL1, GUCY2D, CRX, and RPGRIP1 gene mutations were associated with severely decreased visual acuities beginning within the first year of life. It was also noted that patients with either an RPE65 or CRB1 mutation have progressive visual loss with advancing age. Onset of visual symptoms after infancy was associated with a relatively better visual prognosis.

CONCLUSIONS

The data obtained from this study will help clinicians provide counseling on visual prognosis to patients with known mutations in LCA genes and be of value in future studies aimed at the treatment of LCA and early childhood-onset RP.

From the laboratory to the clinic: molecular genetic testing in pediatric ophthalmology

PURPOSE

To review the current state of molecular genetic testing as it relates to pediatric ophthalmology and to discuss its uses.

DESIGN

Review and evaluation of available molecular genetic testing.

METHODS

Literature review and discussion of testing in practice based on the authors' clinical and laboratory experience.

RESULTS

Fee-for-service testing for many genetic eye diseases now is available. A report is always generated for fee-for-service testing. Detection of DNA variants in genes known to cause eye disease must be interpreted taking into account the variability of the human genome, the presence of benign variants (polymorphisms), and the carrier frequency of recessive alleles. Negative results in genetic testing are helpful in some disorders for which most of the causative genes are known and many disease-causing variants have already been reported, but are less helpful in those that currently have many undiscovered causative genes or novel mutations. Research-based testing also is available, but does not always yield a result. Patients with RPE65-associated Leber congenital amaurosis may be eligible for the current gene therapy trial. Patients with a variety of disorders may benefit from improved surveillance if their genetic diagnosis is known.

CONCLUSIONS

Entry into the genetic testing system often is via the patient's ophthalmologist. Collaboration with geneticists and genetic counselors, use of web sites to keep up with the ever-changing availability and detection rates, and knowledge of clinical trials, when combined with excellent clinical diagnosis, can improve diagnosis and allow eligible patients to participate in treatment trials.

Differential macular morphology in patients with RPE65-, CEP290-, GUCY2D-, and AIPL1-related Leber congenital amaurosis

PURPOSE

To evaluate genotypic and macular morphologic correlations in patients with RPE65-, CEP290-, GUCY2D-, or AIPL1-related Leber congenital amaurosis (LCA) using spectral-domain optical coherence tomography (SD-OCT).

METHODS

SD-OCT macular scans were performed in 21 patients, including 10 with RPE65, 7 with CEP290, 3 with GUCY2D, and 1 with AIPL1 mutations. An image processing software was used to manually draw segmentation lines by three observers. Lamellar structure was evaluated based on the number of retinal layers on segmented images. Total retinal thickness was measured at the central macular and perifoveal areas by using an automated algorithm.

RESULTS

All three patients with GUCY2D mutations (age range, 20-53 years) retained six retinal layers with visible photoreceptor inner/outer segment juncture (PSJ). However, the preservation of lamellar structures did not parallel better visual acuity. Patients with other mutations had poorly defined PSJ and disorganized retinal lamellar structures, where only one to three retinal layers could be observed. Patients with CEP290 mutations trended to have retention of the outer nuclear layer at the fovea and macular thickening, especially at younger ages. In patients with RPE65 (age range, 20-71 years) and AIPL1 mutations (age, 22 years), macular thickness was markedly decreased. Disorganization of retinal lamellar structures in the RPE65 group trended toward a worsening with increasing age.

CONCLUSIONS

Variations of macular microstructures were observed among LCA patients with different genotypes. Disorganization of retinal lamellar structure was generally age related. Preservation of retinal microanatomic structures may not be associated with better visual acuity.

The natural history of stargardt disease with specific sequence mutation in the ABCA4 gene

PURPOSE

To determine longitudinal changes in fundus appearance and visual function in patients with Stargardt with at least one allelic mutation (Gly1961Glu) in the ABCA4 gene.

METHODS

Sixteen patients with a diagnosis of Stargardt disease and a Gly1961Glu mutation were enrolled. All patients underwent a complete ocular examination including best corrected visual acuity, Goldmann visual field (GVF), and full-field ERG examinations. The percentage of patients who showed at least a doubling in the log of the minimum angle of visual resolution (logMAR) between their initial and most recent visits was determined, as was the percentage of patients who showed a doubling in the size of the central scotoma over this duration.

RESULTS

Nine patients had at least a doubling of the logMAR visual acuity in their right eyes and 10 patients in their left eyes, over a mean follow-up (FU) period of 18.6 years. Of 15 patients, 46.7% had equal to or more than a doubling of the central scotoma area in response to a II2e test stimulus in the right eye and 60.0% in the left eyes. Among 10 patients whose ERGs were initially normal for rod and cone responses, 8 remained normal at their most recent FU visit.

CONCLUSIONS

In these patients with Stargardt disease and a Gly1961Glu mutation, most showed a clinical phenotype characterized by fundus changes localized to the foveal and parafoveal regions, normal ERG amplitudes, absence of a silent or masked choroid, and a mean age at initial presentation in the third decade.

A new macular dystrophy with anomalous vascular development, pigment spots, cystic spaces, and neovascularization

OBJECTIVE

To clinically phenotype an inherited macular dystrophy with peculiar intraretinal pigment spots, cysts, and hemorrhage in a 24-year-old female proband and her family.

METHODS

Extended family members of the proband underwent dilated fundus examination, optical coherence tomography, and, in selected cases, fluorescein angiography and electroretinography.

RESULTS

Seventeen family members, representing 3 generations and ranging in age from 5 to 64 years, were clinically examined. Visual acuities ranged from 20/20 to 20/200. Amblyopia and strabismus were frequently present in affected individuals. Consistent with an autosomal dominant pattern of inheritance, 7 family members had multiple central macular cystic spaces and flat, round, densely pigmented spots within the retina. There were right-angle vessels and telangiectasis in the central macula. Two subjects showed evidence of active macular neovascularization with leakage on fluorescein angiography at ages 7 and 24 years, which was responsive to either focal laser or a single injection of bevacizumab. In those cases examined, multifocal electroretinography showed a diminished foveal response.

CONCLUSIONS

This spotted cystic neovascular macular dystrophy appears to represent a new autosomal dominant retinal condition. Because these patients are at risk for choroidal neovascularization, identification of the responsible gene may provide insight into the mechanisms of pathological neovascularization.

Predicting the pathogenicity of RPE65 mutations

To assist in distinguishing disease-causing mutations from nonpathogenic polymorphisms, we developed an objective algorithm to calculate an "estimate of pathogenic probability" (EPP) based on the prevalence of a specific variation, its segregation within families, and its predicted effects on protein structure. Eleven missense variations in the RPE65 gene were evaluated in patients with Leber congenital amaurosis (LCA) using the EPP algorithm. The accuracy of the EPP algorithm was evaluated using a cell-culture assay of RPE65-isomerase activity The variations were engineered into plasmids containing a human RPE65 cDNA and the retinoid isomerase activity of each variant was determined in cultured cells. The EPP algorithm predicted eight substitution mutations to be disease-causing variants. The isomerase catalytic activities of these RPE65 variants were all less than 6% of wild-type. In contrast, the EPP algorithm predicted the other three substitutions to be non-disease-causing, with isomerase activities of 68%, 127%, and 110% of wild-type, respectively. We observed complete concordance between the predicted pathogenicities of missense variations in the RPE65 gene and retinoid isomerase activities measured in a functional assay. These results suggest that the EPP algorithm may be useful to evaluate the pathogenicity of missense variations in other disease genes where functional assays are not available.

Mutations that are a common cause of Leber congenital amaurosis in northern America are rare in southern India

PURPOSE

To test patients from southern India for the presence of mutations that most commonly cause Leber congenital amaurosis (LCA) in northern America.

METHODS

A review of the literature identified 177 unique LCA causing mutations in eight different genes: aryl hydrocarbon receptor interacting protein-like 1 (AIPL1), crumbs homolog 1 (CRB1), cone-rod homeobox (CRX), guanylate cyclase 2D (GUCY2D), nephronophthisis 6 (NPHP6), retinol dehydrogenase 12 (RDH12), retinal pigment epithelium-specific protein 65 kDa (RPE65), and retinitis pigmentosa GTPase regulator interacting protein 1 (RPGRIP1). Allele-specific ligation assay and bidirectional sequencing were used to test 38 unrelated LCA patients from southern India for 104 of these mutations, which contribute to more than 30% of the LCA cases in a northern American population.

RESULTS

Only one participant was found to harbor one of the 104 mutations in the allele-specific assay (homozygous RPE65 Tyr368His). A mutation that was not part of the assay (homozygous RPE65 Tyr143Asp) was incidentally detected in a second patient when an equivocal signal from one allele on the assay was followed up with automated DNA sequencing.

CONCLUSIONS

Mutations that contribute to 30% of the LCA cases in northern America were detected in only 2.6% of LCA cases in our cohort from southern India. There were no instances of IVS26 c.2991+1655 A>G in NPHP6, the most commonly detected mutation in LCA. These data suggest that LCA in India is caused primarily by a different set of mutations in the same genes associated with disease in northern America, or by mutations in other genes that have not yet been discovered. Therefore, mutation-specific assays developed for European and northern American cohorts may not be suited for testing LCA patients from India or other ethnically distinct populations.

Phenotypic variability due to a novel Glu292Lys variation in exon 8 of the BEST1 gene causing best macular dystrophy

OBJECTIVE

To study the phenotypic characteristics of patients with a novel p.E292K mutation in BEST1.

METHODS

Affected individuals underwent ophthalmic examination and testing that included photography, autofluorescence, optical coherence tomography, and electrophysiological testing. Their DNA was analyzed for BEST1 mutations.

RESULTS

Five patients aged 5 to 59 years who expressed the p.E292K mutation in BEST1 were identified in 3 families. Electro-oculographic light-rise was subnormal in all probands and carriers. Carriers had normal findings from fundus examination, multifocal electroretinography, and visual acuity, and were emmetropic or myopic. Only probands had hyperopia and fundus findings typical of Best macular dystrophy. Optical coherence tomography of vitelliform lesions demonstrated retinal pigment epithelium elevation without subretinal fluid; atrophic lesions exhibited disruption of the hyperreflective outer retina-retinal pigment epithelium complex. Intense hyperautofluorescence correlated with the vitelliform lesion.

CONCLUSIONS

Patients with the Glu292Lys variation in BEST1 exhibit intrafamilial and interfamilial phenotypic variability. A disproportionate fraction (26%) of Best disease-causing mutations occurs in exon 8, suggesting that the portion of protein encoded by this exon (amino acids 290-316) may be especially important to bestrophin's function. Relatively good visual acuity with vitelliform lesions can be explained by preservation of the outer retina, demonstrated by optical coherence tomography. Clinical Relevance A novel mutation in this region of BEST1 carries implications for disease pathogenesis.

Peripapillary retinal nerve fiber layer thinning in patients with autosomal recessive cone-rod dystrophy

PURPOSE

To evaluate peripapillary retinal nerve fiber layer (RNFL) thickness using spectral-domain optical coherence tomography in patients with autosomal recessive cone-rod dystrophy (CRD).

DESIGN

Cross-sectional study.

METHODS

Eleven patients (22 eyes) with CRD were studied, including 4 patients with identified ABCA4 gene mutations. Peripapillary RNFL thickness was measured in 16 segments from 4 quadrants. The analyses were based on age and disc size-adjusted normative data. An abnormal thinning was considered when RNFL thickness measurements were less than the fifth percentile in at least 2 of 4 segments in a quadrant. Mean RNFL thickness was compared quantitatively with normative data obtained from 134 subjects.

RESULTS

Eight patients (73%) had peripapillary RNFL thinning in at least 1 quadrant of at least 1 eye, including 3 of 4 patients with known ABCA4 gene mutations. Peripapillary RNFL thinning in the temporal quadrant was seen most commonly in 11 (79%) of 14 eyes with thinning in at least 1 quadrant. Significant thinning of the overall peripapillary RNFL was observed in CRD patients compared with controls (P = .0002). Subgroup analysis showed that 8 (89%) of 9 patients who were older than 40 years had thinning in at least 1 quadrant of at least 1 eye.

CONCLUSIONS

Peripapillary RNFL thinning was observed commonly in our patients with autosomal recessive CRD. The results confirm that the inner retinal structures can be affected in outer retinal disease. Careful evaluation of the inner retina may be important in determining the success rate of potential treatments for predominantly outer retinal diseases.

Localization of complement 1 inhibitor (C1INH/SERPING1) in human eyes with age-related macular degeneration

Age-related macular degeneration (AMD) is a common degenerative disease resulting in injury to the retina, retinal pigment epithelium and choriocapillaris. Recent data from histopathology, animal models and genetic studies have implicated altered regulation of the complement system as a major factor in the incidence and progression of this disease. A variant in the gene SERPING1, which encodes C1INH, an inhibitor of the classical and lectin pathways of complement activation, was recently shown to be associated with AMD. In this study we sought to determine the localization of C1INH in human donor eyes. Immunofluorescence studies using a monoclonal antibody directed against C1INH revealed localization to photoreceptor cells, inner nuclear layer neurons, choriocapillaris, and choroidal extracellular matrix. Drusen did not exhibit labeling. Genotype at rs2511989 did not appear to affect C1INH abundance or localization, nor was it associated with significant molecular weight differences when evaluated by Western blot. In a small number of eyes (n = 7 AMD and n = 7 control) AMD affection status was correlated with increased abundance of choroidal C1INH. These results indicate that C1INH protein is present in the retina and choroid, where it may regulate complement activation.

Mitochondrial Variant G4132A is Associated with Familial Non-Arteritic Anterior Ischemic Optic Neuropathy in One Large Pedigree

OBJECTIVE

To identify the genetic factors associated with familial non-arteritic anterior ischemic optic neuropathy (NA-AION) in a large pedigree.

METHODS

Eleven family members of a single pedigree, including six affected with NA-AION, underwent detailed clinical examinations. The mitochondrial DNA of the proband was sequenced in its entirety in search of disease-causing mutations associated with NA-AION in the pedigree. A control panel comprising 1488 patients suspected of having Leber hereditary optic neuropathy (LHON) and 97 general-population control subjects was screened for the mitochondrial sequence variant identified in the family.

RESULTS

Affected family members were all male and exhibited classic features of NA-AION. Their mean age was 50.2 +/- 5.0 years. A total of 23 sequence variations were detected in the mitochondrial genome of the proband, including one novel sequence variation (G4132A, Ala276Thr) in the NADH dehydrogenase subunit 1 gene (ND1). The G4132A mitochondrial variant was detected in six members of a single pedigree with NA-AION. The G4132A variation was not observed in any of the 1585 subjects in the control panel. Moreover, this variant was not identified in over 2469 ethnically diverse individuals previously evaluated through the Human Mitochondrial Genome Database. None of the three major mutations associated with LHON (G3460A, G11778A, T14484C) were identified in the family.

CONCLUSION

The G4132A mitochondrial variation is associated with familial NA-AION in our pedigree.

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.

CERKL mutations cause an autosomal recessive cone-rod dystrophy with inner retinopathy

PURPOSE

To define the phenotype of the retinal degeneration associated with mutations in the CERKL gene.

METHODS

Six patients (ages, 26-54 years) from three unrelated families with CERKL mutations were studied clinically and by electroretinography, kinetic, and chromatic static perimetry, autofluorescence (AF) imaging, and optical coherence tomography (OCT).

RESULTS

Three siblings were homozygotes for p.R257X mutation; two siblings were compound heterozygotes for p.R257X and a novel p.C362X mutation; and one patient had only p.R257X mutation identified to date. There was a spectrum of severity: from mild visual acuity loss to light perception; from full kinetic fields with relative central scotomas to remnant peripheral islands; from reduced ERGs (some with negative waveforms) to nondetectable signals. Maculopathy showed residual foveal islands or extensive central rod and cone scotomas. With AF imaging, there was evidence of hyperautofluorescence at earlier and hypoautofluorescence at later disease stages. Peripheral function was generally less affected than central function. With OCT there were small foveal islands of outer nuclear layer (ONL) in those with preserved acuity. Eccentric to an annular region with no discernible ONL, there could be ONL in the midperiphery. At early disease stages, ganglion cell layer thickness was less affected than ONL. Later disease stages were accompanied by inner nuclear layer and nerve fiber layer abnormalities.

CONCLUSIONS

CERKL mutations are associated with widespread retinal degeneration with prominent maculopathy. The clinical presentation is that of an autosomal recessive cone-rod dystrophy. Photoreceptor loss appears at all stages of disease and inner laminopathy complicates the phenotype at later stages.

Leber congenital amaurosis caused by Lebercilin (LCA5) mutation: retained photoreceptors adjacent to retinal disorganization

PURPOSE

To determine the retinal disease expression in the rare form of Leber congenital amaurosis (LCA) caused by Lebercilin (LCA5) mutation.

METHODS

Two young unrelated LCA patients, ages six years (P1) and 25 years (P2) at last visit, both with the same homozygous mutation in the LCA5 gene, were evaluated clinically and with noninvasive studies. En face imaging was performed with near-infrared (NIR) reflectance and autofluorescence (AF); cross-sectional retinal images were obtained with optical coherence tomography (OCT). Dark-adapted thresholds were measured in the older patient; and the transient pupillary light reflex was recorded and quantified in both patients.

RESULTS

Both LCA5 patients had light perception vision only, hyperopia, and nystagmus. P1 showed a prominent central island of retinal pigment epithelium (RPE) surrounded by alternating elliptical-appearing areas of decreased and increased pigmentation. Retinal laminar architecture at and near the fovea was abnormal in both patients. Foveal outer nuclear layer (ONL) was present in P1 and P2 but to different degrees. With increasing eccentricity, there was retinal laminar disorganization. Regions of pericentral and midperipheral retina in P1, but not P2, could retain measurable ONL and less laminopathy. P2 had a small central island of perception with >5 log units of sensitivity loss. Pupillary responsiveness was present in both LCA5 patients; the thresholds were abnormally elevated by >or=5.5 log units.

CONCLUSIONS

LCA5 patients had evidence of retained photoreceptors mainly in the central retina. Retinal remodeling was present in pericentral regions in both patients. The NIR reflectance and NIR-AF imaging in the younger patient suggested preserved RPE in retinal regions with retained photoreceptors. Detailed phenotype studies in other LCA5 patients with longitudinal follow-up will help determine the feasibility of future intervention in this rare disease.

CRB1 gene mutations are associated with keratoconus in patients with leber congenital amaurosis

PURPOSE

To present an association of mutations in the CRB1 gene with keratoconus in patients with Leber congenital amaurosis (LCA).

METHODS

Sixteen patients with genotyped LCA (having the CRB1, CRX, RetGC, RPE65, and AIPL1 mutations) were recruited from one ophthalmology practice and examined for the presence of keratoconus. Corneal topography, visual acuity, and slit lamp biomicroscopic examination were performed in all cases.

RESULTS

The mean age of the patients was 34.5 years (range, 13-74). Visual acuities ranged from 20/40 to light perception. Corneal topography was successfully collected in 15 of the cases. Five of the 16 cases had slit lamp and/or topographic features consistent with keratoconus. One patient had a clinical picture that was keratoglobus-like. Of these six cases, four had a CRB1 mutation and two had a CRX mutation. Of the three subjects with the CRX mutation, one had keratoconus, one had the keratoglobus-like presentation, and one was normal. Our cohort represents 14 separate, unrelated families. Only one family comprised multiple members with LCA. These were three affected brothers, one with keratoconus, all with CRB1 mutations.

CONCLUSIONS

Although the results cannot exclude other gene mutations, they suggest that LCA patients with a CRB1 mutation may have a particular susceptibility to keratoconus.

Harmonin in the murine retina and the retinal phenotypes of Ush1c-mutant mice and human USH1C

PURPOSE

To investigate the expression of harmonin in the mouse retina, test for ultrastructural and physiological mutant phenotypes in the retina of an Ush1c mutant mouse, and define in detail the retinal phenotype in human USH1C.

METHODS

Antibodies were generated against harmonin. Harmonin isoform distribution was examined by Western blot analysis and immunocytochemistry. Retinas of deaf circler (dfcr) mice, which possess mutant Ush1c, were analyzed by microscopy and electroretinography (ERG). Two siblings with homozygous 238_239insC (R80fs) USH1C mutations were studied with ERG, perimetry, and optical coherence tomography (OCT).

RESULTS

Harmonin isoforms a and c, but not b are expressed in the retina. Harmonin is concentrated in the photoreceptor synapse where the majority is postsynaptic. Dfcr mice do not undergo retinal degeneration and have normal synaptic ultrastructure and ERGs. USH1C patients had abnormal rod and cone ERGs. Rod- and cone-mediated sensitivities and retinal laminar architecture were normal across 50 degrees -60 degrees of visual field. A transition zone to severely abnormal function and structure was present at greater eccentricities.

CONCLUSIONS

The largest harmonin isoforms are not expressed in the retina. A major retinal concentration of harmonin is in the photoreceptor synapses, both pre- and post-synaptically. The dfcr mouse retina is unaffected by its mutant Ush1c. Patients with USH1C retained regions of normal central retina surrounded by degeneration. Perhaps the human disease is simply more aggressive than that in the mouse. Alternatively, the dfcr mouse may be a model for nonsyndromic deafness, due to the nonpathologic effect of its mutation on the retinal isoforms.