A novel pathogenic CRB1 variant presenting as Leber Congenital Amaurosis 8 and evaluation of gene editing feasibility.

INTRODUCTION: Leber Congenital Amaurosis (LCA) is an inherited retinal disease that presents in infancy with severely decreased vision, nystagmus, and extinguished electroretinography findings. LCA8 is linked to variants in the Crumbs homolog 1 (CRB1) gene. CASE DESCRIPTION: We report a novel CRB1 variant in a 14-year-old male presenting with nystagmus, worsening vision, and inability to fixate on toys in his infancy. Color fundus photography revealed nummular pigments in the macula and periphery. Imaging studies revealed thickened retina on standard domain optical coherence tomography and widespread atrophy of the retinal pigment epithelium on autofluorescence. Full-field electroretinography revealed extinguished scotopic and significantly reduced photopic responses. Genetic testing demonstrated a novel homozygous variant, c.3057 T > A; p.(Tyr1019Ter), in the CRB1 gene. This variant is not currently amenable to base editing, however, in silico analysis revealed several potential prime editing strategies for correction. CONCLUSION: This case presentation is consistent with LCA8, suggesting pathogenicity of this novel variant and expanding our knowledge of disease-causing CRB1 variants.

Analysis of CRB1 Pathogenic Variants Correctable with CRISPR Base and Prime Editing.

The mouse and human retina contain three major Crumbs homologue-1 (CRB1) isoforms. CRB1-A and CRB1-B have cell-type-specific expression patterns making the choice of gene augmentation strategy unclear. Gene editing may be a viable alternative for the amelioration of CRB1-associated retinal degenerations. To assess the prevalence and spectrum of CRB1-associated pathogenic variants amenable to base and prime editing, we carried out an analysis of the Leiden Open Variation Database. Editable variants accounted for 54.5% for base editing and 99.8% for prime editing of all CRB1 pathogenic variants in the Leiden Open Variation Database. The 10 most common editable pathogenic variants for CRB1 accounted for 34.95% of all pathogenic variants, with the c.2843G>A, p.(Cys948Tyr) being the most common editable CRB1 variant. These findings outline the next step toward developing base and prime editing therapeutics as an alternative to gene augmentation for the amelioration of CRB1-associated retinal degenerations.

CRIM1 haploinsufficiency causes defects in eye development in human and mouse.

Colobomatous macrophthalmia with microcornea syndrome (MACOM, Online Mendelian Inheritance in Man (OMIM) 602499) is an autosomal dominantly inherited malformation of the eye, which is characterized by microcornea with increased axial length, coloboma of the iris and of the optic disc, and severe myopia. We performed whole-exome sequencing (WES) in two affected individuals from the 2p23-p16-linked MACOM family, which includes 13 affected individuals in 3 generations. As no shared novel variation was found on the linked haplotype, we performed copy number variation (CNV) analysis by comparing the coverage of all exons in the WES data sets of the 2 patients with the coverage of 26 control exomes. We identified a heterozygous deletion predicted to span 22 kb including exons 14-17 of CRIM1 (cysteine-rich transmembrane bone morphogenetic protein (BMP) regulator 1). Quantitative PCR (qPCR) analysis confirmed the deletion, which was present in 11 affected individuals. Split-read analysis of WES data followed by breakpoint PCR and Sanger sequencing determined both breakpoints flanked by a 4-bp microhomology (CTTG). In the mouse, Crim1 is a growth-factor-binding protein with pleiotropic roles in the development of multiple organs, including the eye. To investigate the role of Crim1 during eye development in mice, we crossed a Crim1(flox) mouse line with the Ap2α-cre mouse line, which expresses Cre in the head surface ectoderm. Strikingly, we observed alterations of eye development in homozygous mice leading to severe anatomical and morphological changes overlapping with the anomalies observed in MACOM patients. Taken together, these findings identify CRIM1 as the causative gene for MACOM syndrome and emphasize the importance of CRIM1 in eye development.

Mutations in LCA5, encoding the ciliary protein lebercilin, cause Leber congenital amaurosis.

Leber congenital amaurosis (LCA) causes blindness or severe visual impairment at or within a few months of birth. Here we show, using homozygosity mapping, that the LCA5 gene on chromosome 6q14, which encodes the previously unknown ciliary protein lebercilin, is associated with this disease. We detected homozygous nonsense and frameshift mutations in LCA5 in five families affected with LCA. In a sixth family, the LCA5 transcript was completely absent. LCA5 is expressed widely throughout development, although the phenotype in affected individuals is limited to the eye. Lebercilin localizes to the connecting cilia of photoreceptors and to the microtubules, centrioles and primary cilia of cultured mammalian cells. Using tandem affinity purification, we identified 24 proteins that link lebercilin to centrosomal and ciliary functions. Members of this interactome represent candidate genes for LCA and other ciliopathies. Our findings emphasize the emerging role of disrupted ciliary processes in the molecular pathogenesis of LCA.

Gene therapy in patient-specific stem cell lines and a preclinical model of retinitis pigmentosa with membrane frizzled-related protein defects.

Defects in Membrane Frizzled-related Protein (MFRP) cause autosomal recessive retinitis pigmentosa (RP). MFRP codes for a retinal pigment epithelium (RPE)-specific membrane receptor of unknown function. In patient-specific induced pluripotent stem (iPS)-derived RPE cells, precise levels of MFRP, and its dicistronic partner CTRP5, are critical to the regulation of actin organization. Overexpression of CTRP5 in naïve human RPE cells phenocopied behavior of MFRP-deficient patient RPE (iPS-RPE) cells. AAV8 (Y733F) vector expressing human MFRP rescued the actin disorganization phenotype and restored apical microvilli in patient-specific iPS-RPE cell lines. As a result, AAV-treated MFRP mutant iPS-RPE recovered pigmentation and transepithelial resistance. The efficacy of AAV-mediated gene therapy was also evaluated in Mfrp(rd6)/Mfrp(rd6) mice--an established preclinical model of RP--and long-term improvement in visual function was observed in AAV-Mfrp-treated mice. This report is the first to indicate the successful use of human iPS-RPE cells as a recipient for gene therapy. The observed favorable response to gene therapy in both patient-specific cell lines, and the Mfrp(rd6)/Mfrp(rd6) preclinical model suggests that this form of degeneration caused by MFRP mutations is a potential target for interventional trials.

Clinical and Therapeutic Evaluation of the Ten Most Prevalent CRB1 Mutations.

Mutations in the Crumbs homolog 1 (CRB1) gene lead to severe inherited retinal dystrophies (IRDs), accounting for nearly 80,000 cases worldwide. To date, there is no therapeutic option for patients suffering from CRB1-IRDs. Therefore, it is of great interest to evaluate gene editing strategies capable of correcting CRB1 mutations. A retrospective chart review was conducted on ten patients demonstrating one or two of the top ten most prevalent CRB1 mutations and receiving care at Columbia University Irving Medical Center, New York, NY, USA. Patient phenotypes were consistent with previously published data for individual CRB1 mutations. To identify the optimal gene editing strategy for these ten mutations, base and prime editing designs were evaluated. For base editing, we adopted the use of a near-PAMless Cas9 (SpRY Cas9), whereas for prime editing, we evaluated the canonical NGG and NGA prime editors. We demonstrate that for the correction of c.2843G>A, p.(Cys948Tyr), the most prevalent CRB1 mutation, base editing has the potential to generate harmful bystanders. Prime editing, however, avoids these bystanders, highlighting its future potential to halt CRB1-mediated disease progression. Additional studies investigating prime editing for CRB1-IRDs are needed, as well as a thorough analysis of prime editing's application, efficiency, and safety in the retina.

Venous Tortuosity in COL4A2-Associated Gould Syndrome.

Mutations in collagen-encoding genes have been linked to numerous systemic diseases. Specifically, pathologic alterations in COL4A2 have been linked to Gould syndrome, a hereditary angiopathy affecting the brain, kidneys, and eyes. However, the ocular phenotype associated with COL4A2-associated disease has yet to be fully characterized. In this report, we describe a novel variant in COL4A2 identified in a 48-year-old woman and her 15-year-old daughter. Funduscopic examination demonstrated significant venous and arteriolar tortuosity. Genetic testing revealed a novel variant, c.2321G>A:p.(Gly774Glu), in COL4A2. This vascular phenotype is similar to the familial retinal arterial tortuosity seen in COL4A2-associated Gould syndrome with additional venous involvement. [Ophthalmic Surg Lasers Imaging Retina 2023;54:536-539.].

Marfan syndrome.

Marfan syndrome (MFS) is an autosomal dominant, age-related but highly penetrant condition with substantial intrafamilial and interfamilial variability. MFS is caused by pathogenetic variants in FBN1, which encodes fibrillin-1, a major structural component of the extracellular matrix that provides support to connective tissues, particularly in arteries, the pericondrium and structures in the eye. Up to 25% of individuals with MFS have de novo variants. The most prominent manifestations of MFS are asymptomatic aortic root aneurysms, aortic dissections, dislocation of the ocular lens (ectopia lentis) and skeletal abnormalities that are characterized by overgrowth of the long bones. MFS is diagnosed based on the Ghent II nosology; genetic testing confirming the presence of a FBN1 pathogenetic variant is not always required for diagnosis but can help distinguish MFS from other heritable thoracic aortic disease syndromes that can present with skeletal features similar to those in MFS. Untreated aortic root aneurysms can progress to life-threatening acute aortic dissections. Management of MFS requires medical therapy to slow the rate of growth of aneurysms and decrease the risk of dissection. Routine surveillance with imaging techniques such as transthoracic echocardiography, CT or MRI is necessary to monitor aneurysm growth and determine when to perform prophylactic repair surgery to prevent an acute aortic dissection.

Compound heterozygous inheritance of two novel COQ2 variants results in familial coenzyme Q deficiency.

BACKGROUND: Primary coenzyme Q10 deficiency is a rare disease that results in diverse and variable clinical manifestations. Nephropathy, myopathy and neurologic involvement are commonly associated, however retinopathy has also been observed with certain pathogenic variants of genes in the coenzyme Q biosynthesis pathway. In this report, we describe a novel presentation of the disease that includes nephropathy and retinopathy without neurological involvement, and which is the result of a compound heterozygous state arising from the inheritance of two recessive potentially pathogenic variants, previously not described. MATERIALS AND METHODS: Retrospective report, with complete ophthalmic examination, multimodal imaging, electroretinography, and whole exome sequencing performed on a family with three affected siblings. RESULTS: We show that affected individuals in the described family inherited two heterozygous variants of the COQ2 gene, resulting in a frameshift variant in one allele, and a predicted deleterious missense variant in the second allele (c.288dupC,p.(Ala97Argfs*56) and c.376C > G,p.(Arg126Gly) respectively). Electroretinography results were consistent with rod-cone dystrophy in the affected individuals. All affected individuals in the family exhibited the characteristic retinopathy as well as end-stage nephropathy, without evidence of any neurological involvement. CONCLUSIONS: We identified two novel compound heterozygous variants of the COQ2 gene that result in primary coenzyme Q deficiency. Targeted sequencing of coenzyme Q biosynthetic pathway genes may be useful in diagnosing oculorenal clinical presentations syndromes not explained by more well known syndromes (e.g., Senior-Loken and Bardet-Biedl syndromes).

Compound heterozygous novel frameshift variants in the PROM1 gene result in Leber congenital amaurosis.

The PROM1 (prominin 1) gene encodes an 865-amino acid glycoprotein that is expressed in retinoblastoma cell lines and in the adult retina. The protein is localized to photoreceptor outer segment disc membranes, where it plays a structural role, and in the retinal pigment epithelium (RPE), where it acts as a cytosolic protein that mediates autophagy. Mutations in PROM1 are typically associated with cone-rod dystrophy 12 (OMIM#3612657), autosomal dominant retinal macular dystrophy 2 (OMIM#608051), autosomal recessive retinitis pigmentosa 41 (OMIM#612095), and Stargardt disease 4 (OMIM#603786). Here we describe the first case of PROM1-associated Leber congenital amaurosis (LCA) in a 12-yr-old Asian male, caused by two not previously described deleterious frameshift variants in the compound heterozygous state. Clinical features include the presence of bull's eye maculopathy, pendular horizontal nystagmus, and photodysphoria consistent with the clinical diagnosis of LCA. The patient was evaluated using ophthalmic imaging, electroretinography, and whole-exome sequencing. Electroretinography revealed extinguished retinal activity.

Aniridia with preserved visual function: a report of four cases with no mutations in PAX6.

PURPOSE: To report four patients with aniridia, preserved visual function, and no detectable mutations in PAX6. DESIGN: Retrospective case series. METHODS: The clinical records and molecular genetic findings of four patients from three clinical practices were reviewed retrospectively. RESULTS: All four patients had anterior segment findings characteristic of aniridia with good vision, no nystagmus in three of four patients, and no mutations on PAX6. An optical coherence tomography study from one of the patients showed a very shallow foveal pit. At the latest examination, none of the patients demonstrated a Wilms tumor. CONCLUSIONS: These four cases provide evidence for genetic heterogeneity in aniridia. In aniridic patients without a PAX6 mutation, vision seems to be relatively well preserved.

Congenital cavitary optic disc anomaly and Axenfeld's anomaly in Wolf-Hirschhorn syndrome: A case report and review of the literature.

BACKGROUND: Wolf-Hirschhorn syndrome is a rare genetic syndrome caused by a heterozygous deletion on chromosome 4p16.3 and is characterized by a "Greek warrior helmet" facies, hypotonia, developmental delay, seizures, structural central nervous system defects, intrauterine growth restriction, sketelal anomalies, cardiac defects, abnormal tooth development, and hearing loss. A variety of ocular manifestations may occur in up to 40% of patients. MATERIALS/METHODS: We report the genetic testing results, systemic findings, and complete ophthalmologic examination findings in a patient with Wolf-Hirschhorn syndrome, including external photography, RetCam3 (Clarity Medical Systems, Pleasonton, CA) goniography, and fundus photography. In addition, we review the literature on ocular manifestations of Wolf-Hirschhorn syndrome. RESULTS: Microarray analysis revealed an unbalanced translocation between 4p16.3-15.3 and Xp22.33-p22.2. Systemic findings included "Greek warrior helmet" facies, hypotonia, cleft palate, neonatal tooth eruption, talipes equinovarus, bilateral clinodactyly, clitoromegaly, partial agenesis of the corpus callosum, bilateral renal hypoplasia, and two atrial septal defects. Ocular findings included normal intraocular pressures and corneal diameters, large-angle exotropia, downward slanting of the palpebral fissures, absent eyelid creases, upper and lower eyelid retraction with shortage of the anterior eyelid lamellae, euryblepharon, lagophthalmos with poor Bell's reflex and exposure keratopathy, hypertelorism, Axenfeld's anomaly, megalopapillae, and cavitary optic disc anomaly. CONCLUSIONS: We describe the ocular phenotype of a patient with Wolf-Hirschhorn syndrome, including the rare descriptions and photographs of Axenfeld's anomaly, megalopapilla, and cavitary optic disc anomaly in this condition.

Missense mutation in SLIT2 associated with congenital myopia, anisometropia, connective tissue abnormalities, and obesity.

BACKGROUND: SLIT2 is a protein ligand for the Roundabout (ROBO) receptor and was found to play a major role in repulsive midline axon guidance in central nervous system development. Based on studies utilizing knockout models, it has been postulated that SLIT2 is important for preventing inappropriate axonal routing during mammalian optic chiasm development. METHODS: Case report. RESULTS: Here, we report a case of congenital myopia, anisometropia, and obesity in a patient with a SLIT2 point mutation. Examination of the patient's skin biopsy revealed abnormalities in elastin and collagen fibrils that suggest an underlying connective tissue disorder. Structural modeling placed the novel mutation (p.D1407G) in the EGF-like domain 8 and was predicted to affect interactions with SLIT2 binding partners. CONCLUSIONS: To the authors' knowledge, this is the first report of a SLIT2 variant in the context of these ocular findings.

Identification of novel mutations in patients with Leber congenital amaurosis and juvenile RP by genome-wide homozygosity mapping with SNP microarrays.

PURPOSE: Leber congenital amaurosis (LCA) and juvenile retinitis pigmentosa (RP) cause severe visual impairment early in life. Thus far, mutations in 13 genes have been associated with autosomal recessive LCA and juvenile RP. The purpose of this study was to use homozygosity mapping to identify mutations in known LCA and juvenile RP genes. METHODS: The genomes of 93 consanguineous and nonconsanguineous patients with LCA and juvenile RP were analyzed for homozygous chromosomal regions by using SNP microarrays. This patient cohort was highly selected, as mutations in the known genes had been excluded with the LCA mutation chip, or a significant number of LCA genes had been excluded by comprehensive mutation analysis. Known LCA and juvenile RP genes residing in the identified homozygous regions were analyzed by sequencing. Detailed ophthalmic examinations were performed on the genotyped patients. RESULTS: Ten homozygous mutations, including seven novel mutations, were identified in the CRB1, LRAT, RPE65, and TULP1 genes in 12 patients. Ten patients were from consanguineous marriages, but in two patients no consanguinity was reported. In 10 of the 12 patients, the causative mutation was present in the largest or second largest homozygous segment of the patient's genome. CONCLUSIONS: Homozygosity mapping using SNP microarrays identified mutations in a significant proportion (30%) of consanguineous patients with LCA and juvenile RP and in a small number (3%) of nonconsanguineous patients. Significant homozygous regions which did not map to known LCA or juvenile RP genes and may be instrumental in identifying novel disease genes were detected in 33 patients.

Biometry Characteristics in Adults and Children With Marfan Syndrome: From the Marfan Eye Consortium of Chicago.

PURPOSE: To report on the biometric findings of adults and children with Marfan syndrome (MFS) recruited from 2 annual National Marfan Foundation conferences (2012 and 2015). DESIGN: Cross-sectional study. METHODS: Subjects diagnosed with MFS by Ghent 2 nosology were included for analysis. Subjects were divided into "adults" (≥16 years of age) and "children" (5-15 years of age). Biometric data included values for refractive error, axial length (AL), corneal curvature, anterior chamber depth, lens thickness, and central corneal thickness. RESULTS: Of the 117 subjects evaluated, 74 (35 adults, 32 children, and 7 children <5 years of age) had a definite diagnosis of MFS and were included in the study. The AL was longer (25.25 ± 0.32 mm vs 24.24 ± 0.33 mm, P = .03) and the lens was thicker (3.94 ± 0.09 mm vs 3.62 ± 0.10 mm, P = .03) in adults. Both groups had flat corneas (average keratometry [Kmed] of 41.59 ± 0.35 diopters [D] in adults vs 40.89 ± 0.36 D in children, P = .17). A negative correlation was found between AL and Kmed (-0.33, P < .001). The corneas of patients with MFS with ectopia lentis (EL) were significantly flatter and with higher degree of corneal astigmatism compared to patients without EL (Kmed of 40.68 ± 0.31 D vs 41.75 ± 0.28 D, P < .01 and corneal astigmatism of 1.68 ± 0.16 D vs 1.13 ± 0.14 D, P = .01). CONCLUSIONS: Children with established MFS have flat corneas at least to the same degree as adults. Corneas of patients with MFS with EL are flatter and have a higher degree of corneal astigmatism. We strongly suggest that corneal parameters should be measured if MFS is suspected, especially in children that may not yet have developed EL.

Comparative data on SD-OCT for the retinal nerve fiber layer and retinal macular thickness in a large cohort with Marfan syndrome.

PURPOSE: To report the distribution of macular and optic nerve topography in the eyes of individuals with Marfan syndrome aged 8-56 years using spectral domain optical coherence tomography (SD-OCT). METHODS: Thirty-three patients with Marfan syndrome underwent a full eye examination including slit-lamp biomicroscopy, indirect ophthalmoscopy, and axial length measurement; and SD-OCT measurements of the retinal nerve fiber layer (RNFL) and macular thickness. RESULTS: For patients between the ages of 8 and 12 years, the average RNFL thickness is 98 ± 9 µm, the vertical cup to disc (C:D) ratio is 0.50 ± 0.10, the central subfield thickness (CST) is 274 ± 38 µm, and the macular volume is 10.3 ± 0.6 mm3. For patients between the ages of 13 and 17 years, the average RNFL is 86 ± 16 µm, the vertical C:D ratio is 0.35 ± 0.20, the CST is 259 ± 15 µm, and the macular volume is 10.1 ± 0.5 mm3. For patients 18 years or older, the average RNFL is 89 ± 12 µm, the vertical C:D ratio is 0.46 ± 0.18, the CST is 262 ± 20 µm, and the macular volume is 10.2 ± 0.4 mm3. When the average RNFL data are compared to a normative, age-adjusted database, 6 of 33 (18%) were thinner than the 5% limit. CONCLUSION: This study reports the distribution of SD-OCT data for patients with Marfan syndrome. Compared to a normative database, 18% of eyes with Marfan syndrome had RNFL thickness < 5% of the population.

Delivery from episcleral exoplants.

PURPOSE: To assess the impact of an episcleral exoplant on transscleral delivery. METHODS: New Zealand White rabbits were given a periocular injection of sodium fluorescein (fluorescein, 376 Da) or an episcleral exoplant loaded with fluorescein. Two types of exoplants were tested: (1) a rigid polyethylene device, impermeable on one side and open to the sclera on the other, that contained compressed pellets of fluorescein and was sutured loosely (apposition group) or tightly to indent the sclera (indentation group) and (2) flexible refillable silicone exoplants also open to the sclera that were secured by suturing, to form a sealed episcleral chamber that was filled with a fluorescein solution. Ocular and plasma fluorophotometry were performed at several time points, and histology was performed to evaluate the effect of exoplants on the periocular tissue. RESULTS: Within 20 minutes of a periocular injection of fluorescein, peak fluorescence was visible in the anterior chamber (AC) and at later time points was displaced toward the retina; at all time points, the highest fluorescence was in the AC. For the polyethylene device indentation group, peak fluorescence was in the retina and posterior vitreous and spread to the AC over time. For the apposition exoplant group, two peaks of fluorescence were seen initially, one in the retina and posterior vitreous and one in the AC. The area under the concentration time curve (AUC +/- SE) for fluorescein concentration was 144.4 +/- 15.1 mug . h/mL for the retinal peak and 43.6 +/- 7.1 mug . h/mL for the posterior vitreous peak after injection of 5 mg of fluorescein into a silicone exoplant, compared with a retinal peak of 3.9 +/- 0.3 and a posterior vitreous peak of 0.99 +/- 0.26 mug . h/mL after periocular injection of 5 mg of fluorescein (P < 0.01 for each). Peak plasma fluorescein levels were significantly reduced in the exoplant group compared with periocular injection. CONCLUSIONS: An episcleral exoplant facilitates diffusion of fluorescein through the sclera resulting in high levels in the retina and posterior vitreous; levels are markedly increased compared with periocular injection of the same amount of fluorescein. It also reduces peak plasma levels indicating reduction of systemic absorption. This procedure provides a new approach that can be combined with sustained-release preparations to optimize delivery of agents to the retina and choroid while minimizing the potential for systemic toxicity.

Genotyping microarray (disease chip) for Leber congenital amaurosis: detection of modifier alleles.

PURPOSE: Leber congenital amaurosis (LCA) is an early-onset inherited disorder of childhood blindness characterized by visual impairment noted soon after birth. Variants in at least six genes (AIPL1, CRB1, CRX, GUCY2D, RPE65, and RPGRIP1) have been associated with a diagnosis consistent with LCA or early-onset retinitis pigmentosa (RP). Genetically heterogeneous inheritance complicates the analyses of LCA cases, especially in patients without a family history of the disorder, and conventional methods are of limited value. METHODS: To overcome these limitations, arrayed primer extension (APEX) technology was used to design a genotyping microarray for early-onset, severe retinal degenerations that includes all of the >300 disease-associated variants currently described in eight genes (in addition to the six just listed, the early-onset RP genes LRAT and MERTK were added). The resultant LCA array allows simultaneous detection of all known disease-associated alleles in any patient with early-onset RP. The array was validated by screening 93 confirmed patients with LCA who had known mutations. Subsequently, 205 novel LCA cases were screened on the array, followed by segregation analyses in families, if applicable. RESULTS: The microarray was >99% effective in determining the existing genetic variation and yielded at least one disease-associated allele in approximately one third of the novel patients. More than two (expected) variants were discovered in a substantial fraction (22/300) of the patients, suggesting a modifier effect from more than one gene. In support of the latter hypothesis, the third allele segregated with a more severe disease phenotype in at least five families. CONCLUSIONS: The LCA genotyping microarray is a robust and cost-effective screening tool, representing the prototype of a disease chip for genotyping patients with a genetically heterogeneous condition. Simultaneous screening for all known LCA-associated variants in large LCA cohorts allows systematic detection and analysis of genetic variation, facilitating prospective diagnosis and ultimately predicting disease progression.