Early-onset Retinal Degeneration Research Articles

Atypical Retinal Phenotype in a Patient With Alström Syndrome and Biallelic Novel Pathogenic Variants in ALMS1, Including a de novo Variation

Alström syndrome (ALMS) is a rare autosomal recessive multi-organ syndrome considered to date as a ciliopathy and caused by variations in ALMS1. Phenotypic variability is well-documented, particularly for the systemic disease manifestations; however, early-onset progressive retinal degeneration affecting both cones and rods (cone-rod type) is universal, leading to blindness by the teenage years. Other features include cardiomyopathy, kidney dysfunction, sensorineural deafness, and childhood obesity associated with hyperinsulinemia and type 2 diabetes mellitus. Here, we present an unusual and delayed retinal dystrophy phenotype associated with ALMS in a 14-year-old female, with affected cone function and surprising complete preservation of rod function on serial electroretinograms (ERGs). High-throughput sequencing of the affected proband revealed compound heterozygosity with two novel nonsense variations in the ALMS1 gene, including one variant of de novo inheritance, an unusual finding in autosomal recessive diseases. To confirm the diagnosis in the context of an unusually mild phenotype and identification of novel variations, we demonstrated the biallelic status of the compound heterozygous variations (c.[286C > T];[1211C > G], p.[(Gln96*)];[(Ser404*)]). This unique case extends our knowledge of the phenotypic variability and the pathogenic variation spectrum in ALMS patients.

Retinal Degeneration Caused by Rod-Specific Dhdds Ablation Occurs without Concomitant Inhibition of Protein N-Glycosylation.

SummaryDehydrodolichyl diphosphate synthase (DHDDS) catalyzes the committed step in dolichol synthesis. Recessive mutations in DHDDS cause retinitis pigmentosa (RP59), resulting in blindness. We hypothesized that rod photoreceptor-specific ablation of Dhdds would cause retinal degeneration due to diminished dolichol-dependent protein N-glycosylation. Dhddsflx/flx mice were crossed with rod-specific Cre recombinase-expressing (Rho-iCre75) mice to generate rod-specific Dhdds knockout mice (Dhddsflx/flx iCre+). In vivo morphological and electrophysiological evaluation of Dhddsflx/flx iCre+ retinas revealed mild retinal dysfunction at postnatal (PN) 4 weeks, compared with age-matched controls; however, rapid photoreceptor degeneration ensued, resulting in almost complete loss of rods and cones by PN 6 weeks. Retina dolichol levels were markedly decreased by PN 4 weeks in Dhddsflx/flx iCre+ mice, relative to controls; despite this, N-glycosylation of retinal proteins, including opsin (the dominant rod-specific glycoprotein), persisted in Dhddsflx/flx iCre+ mice. These findings challenge the conventional mechanistic view of RP59 as a congenital disorder of glycosylation.

Chromatic Full-Field Stimulus Threshold and Pupillography as Functional Markers for Late-Stage, Early-Onset Retinitis Pigmentosa Caused by CRB1 Mutations.

PurposeMutations in the CRB1 gene cause early-onset retinal degeneration (EORD). Clinical disease progression markers, such as visual fields or electrophysiology, are not reliably measurable in most patients to follow the retinal function in patients with CRB1-mutations.MethodsTen patients (five females, five males; age 22–56 years) with EORD caused by CRB1 mutations were examined in a cross-sectional manner using best corrected visual acuity (BCVA), perimetry, full-field and multifocal electroretinography, full-field stimulus threshold (FST), and pupillography to red and blue light. Disease duration was defined as the difference between the age at the first symptoms to the age at examination in years.ResultsBCVA was quantifiable in six patients and ranged from light perception to 20/50. The visual field was measurable only in three patients who had the shortest disease duration. Full-field and multifocal electroretinography were not measurable in any patient. FST to blue and red light were measurable in all patients except the one with the longest disease duration; the thresholds ranged from −16.7 to 1.5 dB for red light and from −40.2 to 2.5 dB for blue light (0 dB = 0.01 cd.s/m2) and showed correlations with disease duration (r = 0.87 for blue, r = 0.65 for red, r = 0.8 for blue–red difference). The maximal relative pupil constriction amplitude (MRA) showed low or no correlations with disease duration (r = −0.55 for blue, r = −0.3 for red light); the blue–red difference in the post-illumination pupil responses (PIPR) showed no correlation with disease duration (r = −0.05). Compared to healthy eyes, the MRA to red and blue light was significantly decreased (P < 0.001) and the blue–red PIPR difference was significantly increased (P = 0.003).ConclusionsFST features a valid clinical marker in late-stage early-onset retinitis pigmentosa caused by CRB1 mutations correlating with disease duration. This indicates the potential as a progression marker of disease. The pupil responses to full-field chromatic stimuli show significant differences from the normal population: the remaining responses, although reduced, indicate a partially preserved inner retinal function despite severe photoreceptor dysfunction.Translational RelevanceThe functional measurements presented in this study present a valid clinical progression marker in late-stage early onset retinitis pigmentosa caused by biallelic CRB1 mutations. Additionally, they can be used as outcome measures for safety and efficacy in clinical therapy trials.

The Liberfarb syndrome, a multisystem disorder affecting eye, ear, bone, and brain development, is caused by a founder pathogenic variant in the PISD gene

PurposeWe observed four individuals in two unrelated but consanguineous families from Portugal and Brazil affected by early-onset retinal degeneration, sensorineural hearing loss, microcephaly, intellectual disability, and skeletal dysplasia with scoliosis and short stature. The phenotype precisely matched that of an individual of Azorean descent published in 1986 by Liberfarb and coworkers. MethodsPatients underwent specialized clinical examinations (including ophthalmological, audiological, orthopedic, radiological, and developmental assessment). Exome and targeted sequencing was performed on selected individuals. Minigene constructs were assessed by quantitative polymerase chain reaction (qPCR) and Sanger sequencing. ResultsAffected individuals shared a 3.36-Mb region of autozygosity on chromosome 22q12.2, including a 10-bp deletion(NM_014338.3:c.904-12_904-3delCTATCACCAC), immediately upstream of the last exon of the PISD (phosphatidylserine decarboxylase) gene. Sequencing of PISD from paraffin-embedded tissue from the 1986 case revealed the identical homozygous variant. In HEK293T cells, this variant led to aberrant splicing of PISD transcripts. ConclusionWe have identified the genetic etiology of the Liberfarb syndrome, affecting brain, eye, ear, bone, and connective tissue. Our work documents the migration of a rare Portuguese founder variant to two continents and highlights the link between phospholipid metabolism and bone formation, sensory defects, and cerebral development, while raising the possibility of therapeutic phospholipid replacement.

Natural History and Genotype-Phenotype Correlations in RDH12-Associated Retinal Degeneration.

Mutations in retinol dehydrogenase 12 (RDH12) cause a severe early-onset retinal degeneration, for which there is no treatment. RDH12 is involved in photoreceptor retinoid metabolism and is a potential target for gene therapy, which has been successful in treating RPE65-associated LCA. RDH12-associated retinal degeneration is particularly devastating due to early macular atrophy, which will likely impact therapeutic outcomes. Defining the unique features and natural history of disease associated with RDH12 mutations is a critical first step in developing treatments. The purpose of this review is to aggregate and summarize the body of literature on phenotypes in RDH12-associated retinal degeneration to help map the natural history of disease and identify phenotypic milestones in disease progression. The results reveal a severe blinding disorder with onset in early childhood and frequent retention of reduced yet useful vision until adolescence. The severity is associated with genotype in some cases. Distinct phenotypic features include macular atrophy followed by bone spicule pigment early in life, in contrast to other forms of LCA which often have a relatively normal fundus appearance in childhood despite severe visual dysfunction. Formal natural history studies are needed to define milestones in disease progression and identify appropriate outcome measures for future therapy trials.

Gene Therapy Rescues Retinal Degeneration in Receptor Expression-Enhancing Protein 6 Mutant Mice.

Hereditary retinal dystrophy is clinically defined as a broad group of chronic and progressive disorders that affect visual function by causing photoreceptor degeneration. Previously, we identified mutations in the gene encoding receptor expression-enhancing protein 6 (REEP6), in individuals with autosomal recessive retinitis pigmentosa (RP), the most common form of inherited retinal dystrophy. One individual was molecularly diagnosed with biallelic REEP6 mutations, a missense mutation over a frameshift mutation. In this study, we generated Reep6 compound heterozygous mice, Reep6L135P/-, which mimic the patient genotype and recapitulate the early-onset retinal degeneration phenotypes observed in the individual with RP. To determine the feasibility of rescuing the Reep6 mutant phenotype via gene replacement therapy, we delivered Reep6.1, the mouse retina-specific isoform of REEP6, to photoreceptors of Reep6 mutant mice on postnatal day 20. Evaluation of the therapeutic effects 2 months posttreatment showed improvements in the photoresponse as well as preservation of photoreceptor cells. Importantly, guanylyl cyclase 1 (GC1) expression was also restored to the outer segment after treatment. Furthermore, rAAV8-Reep6.1 single treatment in Reep6 mutant mice 1 year postinjection showed significant improvements in retinal function and morphology, suggesting that the treatment is effective even after a prolonged period. Findings from this study show that gene replacement therapy in the retina with rAAV overexpressing Reep6 is effective, preserving photoreceptor function in Reep6 mutant mice. These findings provide evidence that rAAV8-based gene therapy can prolong survival of photoreceptors in vivo and can be potentially used as a therapeutic modality for treatment of patients with RP.

The P2Y12 Receptor Antagonist Ticagrelor Reduces Lysosomal pH and Autofluorescence in Retinal Pigmented Epithelial Cells From the ABCA4-/- Mouse Model of Retinal Degeneration.

The accumulation of partially degraded lipid waste in lysosomal-related organelles may contribute to pathology in many aging diseases. The presence of these lipofuscin granules is particularly evident in the autofluorescent lysosome-associated organelles of the retinal pigmented epithelial (RPE) cells, and may be related to early stages of age-related macular degeneration. While lysosomal enzymes degrade material optimally at acidic pH levels, lysosomal pH is elevated in RPE cells from the ABCA4-/- mouse model of Stargardt’s disease, an early onset retinal degeneration. Lowering lysosomal pH through cAMP-dependent pathways decreases accumulation of autofluorescent material in RPE cells in vitro, but identification of an appropriate receptor is crucial for manipulating this pathway in vivo. As the P2Y12 receptor for ADP is coupled to the inhibitory Gi protein, we asked whether blocking the P2Y12 receptor with ticagrelor could restore lysosomal acidity and reduce autofluorescence in compromised RPE cells from ABCA4-/- mice. Oral delivery of ticagrelor giving rise to clinically relevant exposure lowered lysosomal pH in these RPE cells. Ticagrelor also partially reduced autofluorescence in the RPE cells of ABCA4-/- mice. In vitro studies in ARPE-19 cells using more specific antagonists AR-C69931 and AR-C66096 confirmed the importance of the P2Y12 receptor for lowering lysosomal pH and reducing autofluorescence. These observations identify P2Y12 receptor blockade as a potential target to lower lysosomal pH and clear lysosomal waste in RPE cells.

CRISPR-Cas9-Mediated Correction of the 1.02 kb Common Deletion in CLN3 in Induced Pluripotent Stem Cells from Patients with Batten Disease.

Juvenile neuronal ceroid lipofuscinosis (Batten disease) is a rare progressive neurodegenerative disorder caused by mutations in CLN3. Patients present with early-onset retinal degeneration, followed by epilepsy, progressive motor deficits, cognitive decline, and premature death. Approximately 85% of individuals with Batten disease harbor at least one allele containing a 1.02 kb genomic deletion spanning exons 7 and 8. This study demonstrates CRISPR-Cas9-based homology-dependent repair of this mutation in induced pluripotent stem cells generated from two independent patients: one homozygous and one compound heterozygous for the 1.02 kb deletion. Our strategy included delivery of a construct that carried >3 kb of DNA: wild-type CLN3 sequence and a LoxP-flanked, puromycin resistance cassette for positive selection. This strategy resulted in correction at the genomic DNA and mRNA levels in the two independent patient lines. These CRISPR-corrected isogenic cell lines will be a valuable tool for disease modeling and autologous retinal cell replacement.

A mutation in IFT43 causes non-syndromic recessive retinal degeneration.

The aim of this work is to identify the molecular cause of autosomal recessive early onset retinal degeneration in a consanguineous pedigree. Seventeen members of a four-generation Pakistani family were recruited and underwent a detailed ophthalmic examination. Exomes of four affected and two unaffected individuals were sequenced. Variants were filtered using exomeSuite to identify rare potentially pathogenic variants in genes expressed in the retina and/or brain and consistent with the pattern of inheritance. Effect of the variant observed in the gene Intraflagellar Transport Protein 43 (IFT43) was studied by heterologous expression in mIMCD3 and MDCK cells. Expression and sub-cellular localization of IFT43 in the retina and transiently transfected cells was examined by RT-PCR, western blot analysis, and immunohistochemistry. Affected members were diagnosed with early onset non-syndromic progressive retinal degeneration and the presence of bone spicules distributed throughout the retina at younger ages while the older affected members showed severe central choroidal atrophy. Whole-exome sequencing analysis identified a novel homozygous c.100 G > A change in IFT43 segregating with retinal degeneration and not present in ethnicity-matched controls. Immunostaining showed IFT43 localized in the photoreceptors, and to the tip of the cilia in transfected mIMCD3 and MDCK cells. The cilia in mIMCD3 and MDCK cells expressing mutant IFT43 were found to be significantly shorter (P < 0.001) than cells expressing wild-type IFT43. Our studies identified a novel homozygous mutation in the ciliary protein IFT43 as the underlying cause of recessive inherited retinal degeneration. This is the first report demonstrating the involvement of IFT43 in retinal degeneration.

Effects of Subretinal Gene Transfer at Different Time Points in a Mouse Model of Retinal Degeneration

Lysophosphatidylcholine acyltransferase 1 (LPCAT1) is necessary for photoreceptors to generate an important lipid component of their membranes. The absence of LPCAT1 results in early and rapid rod and cone degeneration. Retinal degeneration 11 (rd11) mice carry a mutation in the Lpcat1 gene, and are an excellent model of early-onset rapid retinal degeneration (RD). To date, no reports have documented gene therapy administration in the rd11 mouse model at different ages. In this study, the AAV8 (Y733F)-smCBA-Lpcat1 vector was subretinally injected at postnatal day (P) 10, 14, 18, or 22. Four months after injection, immunohistochemistry and analysis of retinal morphology showed that treatment at P10 rescued about 82% of the wild-type retinal thickness. However, the diffusion of the vector and the resulting rescue were limited to an area around the injection site that was only 31% of the total retinal area. Injection at P14 resulted in vector diffusion that covered approximately 84% of the retina, and we found that gene therapy was more effective against RD when exposure to light was limited before and after treatment. We observed long-term preservation of electroretinogram (ERG) responses, and preservation of retinal structure, indicating that early treatment followed by limited light exposure can improve gene therapy effectiveness for the eyes of rd11 mice. Importantly, delayed treatment still partially preserved M-cones, but not S-cones, and M-cones in the rd11 retina appeared to have a longer window of opportunity for effective preservation with gene therapy. These results provide important information regarding the effects of subretinal gene therapy in the mouse model of LPCAT1-deficiency.

A missense mutation in ASRGL1 is involved in causing autosomal recessive retinal degeneration.

Inherited retinal dystrophies are a group of genetically heterogeneous conditions with broad phenotypic heterogeneity. We analyzed a large five-generation pedigree with early-onset recessive retinal degeneration to identify the causative mutation. Linkage analysis and homozygosity mapping combined with exome sequencing were carried out to map the disease locus and identify the p.G178R mutation in the asparaginase like-1 gene (ASRGL1), segregating with the retinal dystrophy phenotype in the study pedigree. ASRGL1 encodes an enzyme that catalyzes the hydrolysis of L-asparagine and isoaspartyl-peptides. Studies on the ASRGL1 expressed in Escherichia coli and transiently transfected mammalian cells indicated that the p.G178R mutation impairs the autocatalytic processing of this enzyme resulting in the loss of functional ASRGL1 and leaving the inactive precursor protein as a destabilized and aggregation-prone protein. A zebrafish model overexpressing the mutant hASRGL1 developed retinal abnormalities and loss of cone photoreceptors. Our studies suggest that the p.G178R mutation in ASRGL1 leads to photoreceptor degeneration resulting in progressive vision loss.

Canine genome assembly correction facilitates identification of a MAP9 deletion as a potential age of onset modifier for RPGRIP1-associated canine retinal degeneration.

Retinal degeneration (RD) in the Miniature Long Haired Dachshund (MLHD) is a cone-rod dystrophy resulting in eventual blindness in affected individuals. In a previous study, a 44-nucleotide insertion (ins44) in exon 2 of RPGRIP1 was associated with RD. However, results on an extended population of MLHD revealed a variable RD onset age for ins44 homozygous dogs. Further investigations using a genome-wide association study comparing early onset and late onset RD cases identified an age of onset modifying locus for RD, approximately 30Mb upstream of RPGRIP1 on chr15. In this investigation, target enriched sequencing identified a MAP9 deletion spanning approximately 22kb associated with early RD onset. Identification of the deletion required correction to the CanFam3.1 genome build as canine MAP9 is part of a historic tandem duplication, resulting in incomplete assembly of this genome region. The deletion breakpoints were identified in MAP9 intron 10 and in a downstream partial MAP9 pseudogene. The fusion of these two genes, which we have called MAP9 EORD (microtubule-associated protein, early onset retinal degeneration), is in frame and is expressed at the RNA level, with the 3' region containing several predicted deleterious variants. We speculate that MAP9 associates with α-tubulin in the basal body of the cilium. RPGRIP1 is also known to locate to the cilium, where it is closely associated with RPGR. RPGRIP1 mutations also cause redistribution of α-tubulin away from the ciliary region in photoreceptors. Hence, a MAP9 partial deficit is a particularly attractive candidate to synergise with a partial RPGRIP1 deficit to cause a more serious disease.

Ciliopathy-associated protein CEP290 modifies the severity of retinal degeneration due to loss of RPGR

Mutations in RPGR (retinitis pigmentosa GTPase regulator) are the most common cause of X-linked RP, a severe blindness disorder. RPGR mutations result in clinically variable disease with early- to late-onset phenotypic presentation. Molecular mechanisms underlying such heterogeneity are unclear. Here we show that phenotypic expression of Rpgr-loss in mice is influenced genetically by the loss of Cep290, a human ciliopathy gene. We found that Rpgrko/Y mice with a heterozygous hypomorphic allele of Cep290 (Cep290rd16/+) but not of a heterozygous null allele of Cep290 (Cep290null/+) or of other ciliopathy genes, Rpgrip1, Nphp1, Nphp4 and Nphp5, exhibit relatively early onset (by 3 months of age) retinal degeneration and dysfunction when compared with the onset at ∼7 months of age in the Rpgrko/Y mice. We also observed disorganized photoreceptor outer-segment morphology and defective trafficking of opsins in the Rpgrko/Y::Cep290rd16/+ mice. Together with a physical interaction between RPGR and the C-terminal domain of CEP290, our data suggest that RPGR and CEP290 genetically interact and highlight the involvement of hypomorphic alleles of genes as potential modifiers of heterogeneous retinal ciliopathies.

FAM161A and TTC8 are Differentially Expressed in Non-Allelelic Early Onset Retinal Degeneration.

Ciliary genes FAM161A and TTC8 have been implicated in retinal degeneration (RD) in humans and in dogs. The identification of FAM161A and TTC8 mutations in canine RD is exciting as there is the potential to develop novel large animal models for RD. However, the disease phenotypes in the dog and the roles of abnormal genes in disease pathology have yet to be fully characterized. The present study evaluated the expression patterns of FAM161A and TTC8 during normal retinal development in dogs, and in three non-allelic, early onset canine RD models at critical time points of the disease: RCD1, XLPRA2 and ERD. Both genes were differentially expressed in RCD1 and ERD, but not in XLPRA2. These results add evidence to the hypothesis that (a) mutations in many retinal genes have a cascade effect on the expression of multiple, possibly unrelated genes and (b) a large number and wide range of genes probably contribute to RD in general.

Investigating the Molecular Basis of Retinal Degeneration in a Familial Cohort of Pakistani Decent by Exome Sequencing.

PurposeTo define the molecular basis of retinal degeneration in consanguineous Pakistani pedigrees with early onset retinal degeneration.MethodsA cohort of 277 individuals representing 26 pedigrees from the Punjab province of Pakistan was analyzed. Exomes were captured with commercial kits and sequenced on an Illumina HiSeq 2500. Candidate variants were identified using standard tools and analyzed using exomeSuite to detect all potentially pathogenic changes in genes implicated in retinal degeneration. Segregation analysis was performed by dideoxy sequencing and novel variants were additionally investigated for their presence in ethnicity-matched controls.ResultsWe identified a total of nine causal mutations, including six novel variants in RPE65, LCA5, USH2A, CNGB1, FAM161A, CERKL and GUCY2D as the underlying cause of inherited retinal degenerations in 13 of 26 pedigrees. In addition to the causal variants, a total of 200 variants each observed in five or more unrelated pedigrees investigated in this study that were absent from the dbSNP, HapMap, 1000 Genomes, NHLBI ESP6500, and ExAC databases were identified, suggesting that they are common in, and unique to the Pakistani population.ConclusionsWe identified causal mutations associated with retinal degeneration in nearly half of the pedigrees investigated in this study through next generation whole exome sequencing. All novel variants detected in this study through exome sequencing have been cataloged providing a reference database of variants common in, and unique to the Pakistani population.

Destructive Changes in the Neuronal Structure of the FVB/N Mouse Retina.

We applied a series of selective antibodies for labeling the various cell types in the mammalian retina. These were used to identify the progressive loss of neurons in the FVB/N mouse, a model of early onset retinal degeneration produced by a mutation in the pde6b gene. The immunocytochemical studies, together with electroretinogram (ERG) recordings, enabled us to examine the time course of the degenerative changes that extended from the photoreceptors to the ganglion cells at the proximal end of the retina. Our study indicates that photoreceptors in FVB/N undergo a rapid degeneration within three postnatal weeks, and that there is a concomitant loss of retinal neurons in the inner nuclear layer. Although the loss of rods was detected at an earlier age during which time M- and S-opsin molecules were translocated to the cone nuclei; by 6 months all cones had also degenerated. Neuronal remodeling was also seen in the second-order neurons with horizontal cells sprouting processes proximally and dendritic retraction in rod-driven bipolar cells. Interestingly, the morphology of cone-driven bipolar cells were affected less by the disease process. The cellular structure of inner retinal neurons, i.e., ChAT amacrine cells, ganglion cells, and melanopsin-positive ganglion cells did not exhibit any gross changes of cell densities and appeared to be relatively unaffected by the massive photoreceptor degeneration in the distal retina. However, Muller cell processes began to express GFAP at their endfeet at p14, and it climbed progressively to the cell’s distal ends by 6 months. Our study indicates that FVB/N mouse provides a useful model with which to assess possible intervention strategies to arrest photoreceptor death in related diseases.

Animals deficient in C2Orf71, an autosomal recessive retinitis pigmentosa-associated locus, develop severe early-onset retinal degeneration.

Genetic mapping was recently used to identify the underlying cause for a previously uncharacterized cohort of autosomal recessive retinitis pigmentosa cases. Genetic mapping of affected individuals resulted in the identification of an uncharacterized gene, C2Orf71, as the causative locus. However, initial homology searches failed to reveal similarities to any previously characterized protein or domain. To address this issue, we characterized the mouse homolog, BC027072. Immunohistochemistry with a custom polyclonal antibody showed staining localized to the inner segments (IS) of photoreceptor cells, as well as the outer segments (OS) of cone cells. A knockout mouse line (BC(-/-)) was generated and demonstrated that loss of this gene results in a severe, early-onset retinal degeneration. Histology and electron microscopy (EM) revealed disorganized OS as early as 3 weeks with complete loss by 24 weeks of age. EM micrographs displayed packets of cellular material containing OS discs or IS organelles in the OS region and abnormal retinal pigmented epithelium cells. Analyses of retinoids and rhodopsin levels showed <20% in BC(-/-) versus wild-type mice early in development. Electroretinograms demonstrated that affected mice were virtually non-responsive to light by 8 weeks of age. Lastly, RNAseq analysis of ocular gene expression in BC(-/-) mice revealed clues to the causes of the progressive retinal degenerations. Although its function remains unknown, this protein appears essential for normal OS development/maintenance and vision in humans and mice. RNAseq data are available in the GEO database under accession: GSE63810.

TULP1 mutations causing early-onset retinal degeneration: preserved but insensitive macular cones.

To investigate visual function and outer and inner retinal structure in the rare form of retinal degeneration (RD) caused by TULP1 (tubby-like protein 1) mutations. Retinal degeneration patients with TULP1 mutations (n = 5; age range, 5-36 years) were studied by kinetic and chromatic static perimetry, en face autofluorescence imaging, and spectral-domain optical coherence tomography (OCT) scans. Outer and inner retinal laminar thickness were measured and mapped across the central retina. Comparisons were made with results from patients with RD associated with four ciliopathy genotypes (MAK, RPGR, BBS1, and USH2A). The TULP1-RD patients were severely affected already in the first decade of life and there was rapidly progressive visual loss. No evidence of rod function was present at any age. Small central islands showed melanized retinal pigment epithelium by autofluorescence imaging and well-preserved photoreceptor laminar thickness by OCT imaging. There was extracentral loss of laminar architecture and increased inner retinal thickening. Structure-function relationships in residual foveal cone islands were made in TULP1-RD patients and in other retinopathies considered ciliopathies. Patients with TULP1-RD, unlike the others, had greater dysfunction for the degree of foveal structural preservation. Retinal degeneration with TULP1 mutations leads to a small central island of residual foveal cones at early ages. These cones are less sensitive than expected from the residual structure. The human phenotype is consistent with experimental evidence in the Tulp1 knockout mouse model that visual dysfunction could be complicated by abnormal processes proximal to cone outer segments.

Renal-retinal ciliopathy gene Sdccag8 regulates DNA damage response signaling.

Nephronophthisis-related ciliopathies (NPHP-RCs) are developmental and degenerative kidney diseases that are frequently associated with extrarenal pathologies such as retinal degeneration, obesity, and intellectual disability. We recently identified mutations in a gene encoding the centrosomal protein SDCCAG8 as causing NPHP type 10 in humans. To study the role of Sdccag8 in disease pathogenesis, we generated a Sdccag8 gene-trap mouse line. Homozygous Sdccag8(gt/gt) mice lacked the wild-type Sdccag8 transcript and protein, and recapitulated the human phenotypes of NPHP and retinal degeneration. These mice exhibited early onset retinal degeneration that was associated with rhodopsin mislocalization in the photoreceptors and reduced cone cell numbers, and led to progressive loss of vision. By contrast, renal histologic changes occurred later, and no global ciliary defects were observed in the kidneys. Instead, renal pathology was associated with elevated levels of DNA damage response signaling activity. Cell culture studies confirmed the aberrant activation of DNA damage response in Sdccag8(gt/gt)-derived cells, characterized by elevated levels of γH2AX and phosphorylated ATM and cell cycle profile abnormalities. Our analysis of Sdccag8(gt/gt) mice indicates that the pleiotropic phenotypes in these mice may arise through multiple tissue-specific disease mechanisms.

Homozygous loss‐of‐function mutation of the LEPREL1 gene causes severe non‐syndromic high myopia with early‐onset cataract

High myopia is a severe visual impairment which can increase the risk of retinal degeneration, subretinal hemorrhage, choroidal neovascularization, cataract and retinal detachment. We recruited an autosomal-recessive high myopia family, with affected subjects who also present early-onset cataract, retinal degeneration and other complications. Using targeted capturing and whole exome sequencing, we identified a homozygous non-sense mutation in the LEPREL1 gene which causes premature termination of the translation at the fifth amino acid (c.13C>T; p.Q5X), co-segregating with the phenotypes. LEPREL1 encodes a proline hydroxylase called prolyl 3-hydroxylase 2 (P3H2), a 2-oxoglutarate-dependent dioxygenase that hydroxylates collagens. The results show that LEPREL1 plays an important role in eye development and homozygous loss-of-function mutation of this gene can cause severely high myopia and early-onset cataract. Our study also strongly suggests that the disruption of collagen modification is one of the pathogenic mechanisms of high myopia and cataract.