Clinical and molecular characterization of non-syndromic retinal dystrophy due to c.175G>A mutation in ceroid lipofuscinosis neuronal 3 (CLN3)

Multimodal and longitudinal evaluation of novel phenotype-genotype correlation of CLN3 isolated retinal degeneration in an hispanic female with heterozygous mutations c.944dup and c.1305C>G

BACKGROUND

Inherited retinal disorders (IRDs) are a complex group of heritable diseases which are characterized by rod, cone, retinal pigment epithelium, or optic nerve dysfunction. Recently, mutations in CLN3 have also been associated with isolated IRDs. Herein, a case with heterozygous CLN3 variations that had not been previously linked to a CLN3-isolated retinal degeneration (CLN3IRD) phenotype in a Hispanic female and its multimodal imaging findings across a 10-year follow-up are presented.

MATERIAL AND METHODS

An observational, prospective, case report on a hispanic female with CLN3IRD is presented. Patients underwent genetic testing and color fundus photography (CFC) and autofluorescence (FAF), fluorescein angiography (FA), Spectral domain optical coherence tomography (OCT) of the macular area, electroretinogram (ERG) and 30-2 visual field examination through automated perimetry.

RESULTS

A female, aged 24, affected by CLN3IRD phenotype from c.944dup and c.1305C>G compound heterozygous variants, presented with bilateral hypopigmentary changes in the macular area of OU with that corresponded to hyporautofluorescent deposits in the macular area on FAF. An atrophic maculopathy was evident on structural OCT, and FA disclosed a symmetrical macular hyperflourescence with staining in the early and late stages in OU. Humphrey visual field testing showed a marked reduction of the central visual field in OU. Electrophysiological testing revealed an ERG with markedly decreased a and b waves in OU. In ten years follow up developed of bone spiculae in the midperipheral retina.

CONCLUSIONS

We reported a patient with a novel CLN3IRD severe phenotype associated with the variants c.944dup and c.1305C>G, which had previously only been associated with JCNL.

Expanding the phenotypic and genotypic spectrum of patients with HGSNAT-related retinopathy

BACKGROUND

Variants in HGSNAT have historically been associated with syndromic mucopolysaccharidosis type IIIC (MPSIIIC) but more recent studies demonstrate cases of HGSNAT-related non-syndromic retinitis pigmentosa. We describe and expand the genotypic and phenotypic spectrum of this disease.

MATERIALS AND METHODS

This is a retrospective, observational, case series of 11 patients with pericentral retinitis pigmentosa due to variants in HGSNAT gene without a syndromic diagnosis of MPSIIIC. We reviewed ophthalmologic data extracted from medical records, genetic testing, color fundus photos, fundus autofluorescence (FAF), and optical coherence tomography (OCT).

RESULTS

Of the 11 patients, the mean age was 52 years (range: 26-78). The mean age of ophthalmologic symptoms onset was 45 years (range: 15-72). The visual acuity varied from 20/20 to 20/80 (mean 20/30 median 20/20). We described five novel variants in HGSNAT: c.715del (p.Arg239Alafs *37), c.118 G>A (p.Asp40Asn), c.1218_1220delinsTAT, c.1297A>G (p.Asn433Asp), and c.1726 G>T (p.Gly576*).

CONCLUSIONS

HGSNAT has high phenotypic heterogeneity. Data from our cohort showed that all patients who had at least one variant of c.1843 G>A (p.Ala615Thr) presented with the onset of ocular symptoms after the fourth decade of life. The two patients with onset of ocular symptoms before the fourth decade did not carry this variant. This may suggest that c.1843 G>A variant is associated with a later onset of retinopathy.

Ongoing retinal degeneration despite intraventricular enzyme replacement therapy with cerliponase alfa in late-infantile neuronal ceroid lipofuscinosis type 2 (CLN2 disease)

BACKGROUND/AIMS

Late-infantile neuronal ceroid lipofuscinosis type 2 (CLN2) is a neurodegenerative, blinding lysosomal storage disorder. The purpose of the current study was to characterise the progression of CLN2-associated retinal degeneration in patients under intraventricular enzyme replacement therapy (ERT) with cerliponase alfa.

METHODS

We analysed visual function, retinal morphology and neuropaediatric data using preferential looking test (PLT), Weill Cornell Batten Scale (WCBS), optical coherence tomography (OCT) imaging and the Hamburg Motor-Language late-infantile neuronal ceroid lipofuscinosis (LINCL) Scale (M-L scale).

RESULTS

Fifty-six eyes of 28 patients had baseline PLT, WCBS and OCT. 15 patients underwent serial examinations, resulting in a total of 132 OCT scans and WCBS results, 66 Hamburg M-L scores and 49 PLT results during a mean follow-up time of 18.2 months (range 5-40). A negative correlation (r=-0.69, p<0.001) was found between central retinal thickness (CRT) values and age at examination with a maximal annual decrease of 23 µm between 56 and 80 months of age. A significant correlation was observed between PLT results and the age at examination (r=0.46, p=0.001), the WCBS scores (r=0.62; p<0.001) and CRT values (r=-0.64; p<0.001). The M-L score correlated with the ocular measurements (CRT: r=0.58, p<0.001; WCBS r=-0.64, p<0.001; PLT score: r=-0.57, p<0.001).

CONCLUSION

Despite intraventricular ERT, retinal degeneration progressed in patients with CLN2 and was particularly pronounced between 56 and 80 months of age. Retina-directed therapies should therefore be initiated before or as early as possible during the phase of rapid retinal degeneration. PLT and WCBS were identified as valuable outcome measures to monitor disease progression.

TRIAL REGISTRATION NUMBER

NCT04613089.

Systematic assessment of the contribution of structural variants to inherited retinal diseases

Despite increasing success in determining genetic diagnosis for patients with inherited retinal diseases (IRDs), mutations in about 30% of the IRD cases remain unclear or unsettled after targeted gene panel or whole exome sequencing. In this study, we aimed to investigate the contributions of structural variants (SVs) to settling the molecular diagnosis of IRD with whole-genome sequencing (WGS). A cohort of 755 IRD patients whose pathogenic mutations remain undefined were subjected to WGS. Four SV calling algorithms including include MANTA, DELLY, LUMPY and CNVnator were used to detect SVs throughout the genome. All SVs identified by any one of these four algorithms were included for further analysis. AnnotSV was used to annotate these SVs. SVs that overlap with known IRD-associated genes were examined with sequencing coverage, junction reads and discordant read pairs. Polymerase Chain Reaction (PCR) followed by Sanger sequencing was used to further confirm the SVs and identify the breakpoints. Segregation of the candidate pathogenic alleles with the disease was performed when possible. A total of 16 candidate pathogenic SVs were identified in 16 families, including deletions and inversions, representing 2.1% of patients with previously unsolved IRDs. Autosomal dominant, autosomal recessive and X-linked inheritance of disease-causing SVs were observed in 12 different genes. Among these, SVs in CLN3, EYS and PRPF31 were found in multiple families. Our study suggests that the contribution of SVs detected by short-read WGS is about 0.25% of our IRD patient cohort and is significantly lower than that of single nucleotide changes and small insertions and deletions.

Early recognition of CLN3 disease facilitated by visual electrophysiology and multimodal imaging

BACKGROUND

Neuronal ceroid lipofuscinosis is a group of neurodegenerative disorders with varying visual dysfunction. CLN3 is a subtype which commonly presents with visual decline. Visual symptomatology can be indistinct making early diagnosis difficult. This study reports ocular biomarkers of CLN3 patients to assist clinicians in early diagnosis, disease monitoring, and future therapy.

METHODS

Retrospective review of 5 confirmed CLN3 patients in our eye clinic. Best corrected visual acuity (BCVA), electroretinogram (ERG), ultra-widefield (UWF) fundus photography and fundus autofluorescence (FAF), and optical coherence tomography (OCT) studies were undertaken.

RESULTS

Five unrelated children, 4 females and 1 male, with median age of 6.2 years (4.6-11.7) at first assessment were investigated at the clinic from 2016 to 2021. Four homozygous and one heterozygous pathogenic CLN3 variants were found. Best corrected visual acuities (BCVAs) ranged from 0.18 to 0.88 logMAR at first presentation. Electronegative ERGs were identified in all patients. Bull's eye maculopathies found in all patients. Hyper-autofluorescence ring surrounding hypo-autofluorescence fovea on FAF was found. Foveal ellipsoid zone (EZ) disruptions were found in all patients with additional inner and outer retinal microcystic changes in one patient. Neurological problems noted included autism, anxiety, motor dyspraxia, behavioural issue, and psychomotor regression.

CONCLUSIONS

CLN3 patients presented at median age 6.2 years with visual decline. Early onset maculopathy with an electronegative ERG and variable cognitive and motor decline should prompt further investigations including neuropaediatric evaluation and genetic assessment for CLN3 disease. The structural parameters such as EZ and FAF will facilitate ocular monitoring.

Phenotypic Variability of Retinal Disease Among a Cohort of Patients With Variants in the CLN Genes

Purpose

To describe the phenotype of CLN-associated retinal dystrophy in a subset of patients at the Columbia University Medical Center, United States, and the Hospital das Clínicas de Pernambuco, Brazil, in comparison to the published literature.

Methods

Eleven patients with confirmed biallelic variants in the CLN genes were evaluated via dilated fundus examination, clinical imaging, and full-field electroretinogram. A thorough literature search was conducted to determine previously published variants and associated phenotypes.

Results

Genetic testing confirmed the presence of variants in CLN3, CLN7/MFSD8, CLN8, and GRN/CLN11. Five novel variants were identified, and four novel phenotypes of previously published alleles were described. The phenotype differed among patients with variants in the same gene and sometimes among patients with the same allele.

Conclusions

Substantial phenotypic variability among variants in the CLN genes makes identification of genotype-phenotype or allele-phenotype correlations challenging. Further study is required to establish an extensive database for adequate patient counseling.

Systematic assessment of the contribution of structural variants to inherited retinal diseases

Despite increasing success in determining genetic diagnosis for patients with inherited retinal diseases (IRDs), mutations in about 30% of the IRD cases remain unclear or unsettled after targeted gene panel or whole exome sequencing. In this study, we aimed to investigate the contributions of structural variants (SVs) to settling the molecular diagnosis of IRD with whole-genome sequencing (WGS). A cohort of 755 IRD patients whose pathogenic mutations remain undefined was subjected to WGS. Four SV calling algorithms including include MANTA, DELLY, LUMPY, and CNVnator were used to detect SVs throughout the genome. All SVs identified by any one of these four algorithms were included for further analysis. AnnotSV was used to annotate these SVs. SVs that overlap with known IRD-associated genes were examined with sequencing coverage, junction reads, and discordant read pairs. PCR followed by Sanger sequencing was used to further confirm the SVs and identify the breakpoints. Segregation of the candidate pathogenic alleles with the disease was performed when possible. In total, sixteen candidate pathogenic SVs were identified in sixteen families, including deletions and inversions, representing 2.1% of patients with previously unsolved IRDs. Autosomal dominant, autosomal recessive, and X-linked inheritance of disease-causing SVs were observed in 12 different genes. Among these, SVs in CLN3, EYS, PRPF31 were found in multiple families. Our study suggests that the contribution of SVs detected by short-read WGS is about 0.25% of our IRD patient cohort and is significantly lower than that of single nucleotide changes and small insertions and deletions.

Top-down and bottom-up propagation of disease in the neuronal ceroid lipofuscinoses

Background

The Neuronal Ceroid Lipofuscinoses (NCLs) may be considered distinct neurodegenerative disorders with separate underlying molecular causes resulting from monogenetic mutations. An alternative hypothesis is to consider the NCLs as related diseases that share lipofuscin pathobiology as the common core feature, but otherwise distinguished by different a) initial anatomic location, and b) disease propagation.

Methods

We have tested this hypothesis by comparing known differences in symptomatology and pathology of the CLN1 phenotype caused by complete loss of PPT1 function (i.e., the classical infantile form) and of the classical juvenile CLN3 phenotype. These two forms of NCL represent early onset and rapidly progressing vs. late onset and slowly progressing disease modalities respectively.

Results

Despite displaying similar pathological endpoints, the clinical phenotypes and the evidence of imaging and postmortem studies reveal strikingly different time courses and distributions of disease propagation. Data from CLN1 disease are indicative of disease propagation from the body, with early effects within the spinal cord and subsequently within the brainstem, the cerebral hemispheres, cerebellum and retina. In contrast, the retina appears to be the most vulnerable organ in CLN3, and the site where pathology is first present. Pathology subsequently is present in the occipital connectome of the CLN3 brain, followed by a top-down propagation in which cerebral and cerebellar atrophy in early adolescence is followed by involvement of the peripheral nerves in later adolescence/early twenties, with the extrapyramidal system also affected during this time course.

Discussion

The propagation of disease in these two NCLs therefore has much in common with the “Brain-first” vs. “Body-first” models of alpha-synuclein propagation in Parkinson's disease. CLN1 disease represents a “Body-first” or bottom-up disease propagation and CLN3 disease having a “Brain-first” and top-down propagation. It is noteworthy that the varied phenotypes of CLN1 disease, whether it starts in infancy (infantile form) or later in childhood (juvenile form), still fit with our proposed hypothesis of a bottom-up disease propagation in CLN1. Likewise, in protracted CLN3 disease, where both cognitive and motor declines are delayed, the initial manifestations of disease are also seen in the outer retinal layers, i.e., identical to classical Juvenile NCL disease.

Contribution of Whole-Genome Sequencing and Transcript Analysis to Decipher Retinal Diseases Associated with MFSD8 Variants

Biallelic gene defects in MFSD8 are not only a cause of the late-infantile form of neuronal ceroid lipofuscinosis, but also of rare isolated retinal degeneration. We report clinical and genetic data of seven patients compound heterozygous or homozygous for variants in MFSD8, issued from a French cohort with inherited retinal degeneration, and two additional patients retrieved from a Swiss cohort. Next-generation sequencing of large panels combined with whole-genome sequencing allowed for the identification of twelve variants from which seven were novel. Among them were one deep intronic variant c.998+1669A>G, one large deletion encompassing exon 9 and 10, and a silent change c.750A>G. Transcript analysis performed on patients’ lymphoblastoid cell lines revealed the creation of a donor splice site by c.998+1669A>G, resulting in a 140 bp pseudoexon insertion in intron 10. Variant c.750A>G produced exon 8 skipping. In silico and in cellulo studies of these variants allowed us to assign the pathogenic effect, and showed that the combination of at least one severe variant with a moderate one leads to isolated retinal dystrophy, whereas the combination in trans of two severe variants is responsible for early onset severe retinal dystrophy in the context of late-infantile neuronal ceroid lipofuscinosis.

Retinal Phenotype of Patients With Isolated Retinal Degeneration Due to CLN3 Pathogenic Variants in a French Retinitis Pigmentosa Cohort

Importance

Biallelic variants in CLN3 lead to a spectrum of diseases, ranging from severe neurodegeneration with retinal involvement (juvenile neuronal ceroid lipofuscinosis) to retina-restricted conditions.

Objective

To provide a detailed description of the retinal phenotype of patients with isolated retinal degeneration harboring biallelic CLN3 pathogenic variants and to attempt a phenotype-genotype correlation associated with this gene defect.

Design, Setting, and Participants

This retrospective cohort study included patients carrying biallelic CLN3 variants extracted from a cohort of patients with inherited retinal disorders (IRDs) investigated at the National Reference Center for Rare Ocular Diseases of the Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts from December 2007 to August 2020. Data were analyzed from October 2019 to August 2020.

Main Outcome and Measures

Functional (best-corrected visual acuity, visual field, color vision, and full-field electroretinogram), morphological (multimodal retinal imaging), and clinical data from patients were collected and analyzed. Gene defect was identified by either next-generation sequencing or whole-exome sequencing and confirmed by Sanger sequencing, quantitative polymerase chain reaction, and cosegregation analysis.

Results

Of 1533 included patients, 843 (55.0%) were women and 690 (45.0%) were men. A total of 15 cases from 11 unrelated families harboring biallelic CLN3 variants were identified. All patients presented with nonsyndromic IRD. Two distinct patterns of retinal disease could be identified: a mild rod-cone degeneration of middle-age onset (n = 6; legal blindness threshold reached by 70s) and a severe retinal degeneration with early macular atrophic changes (n = 9; legal blindness threshold reached by 40s). Eleven distinct pathogenic variants were detected, of which 4 were novel. All but 1, p.(Arg405Trp), CLN3 point variants and their genotypic associations were clearly distinct between juvenile neuronal ceroid lipofuscinosis and retina-restricted disease. Mild and severe forms of retina-restricted CLN3-linked IRDs also had different genetic background.

Conclusions and Relevance

These findings suggest CLN3 should be included in next-generation sequencing panels when investigating patients with nonsyndromic rod-cone dystrophy. These results document phenotype-genotype correlations associated with specific variants in CLN3. However, caution seems warranted regarding the potential neurological outcome if a pathogenic variant in CLN3 is detected in a case of presumed isolated IRD for the onset of neurological symptoms could be delayed.

Unique Variant Spectrum in a Jordanian Cohort with Inherited Retinal Dystrophies

Whole Exome Sequencing (WES) is a powerful approach for detecting sequence variations in the human genome. The aim of this study was to investigate the genetic defects in Jordanian patients with inherited retinal dystrophies (IRDs) using WES. WES was performed on proband patients' DNA samples from 55 Jordanian families. Sanger sequencing was used for validation and segregation analysis of the detected, potential disease-causing variants (DCVs). Thirty-five putatively causative variants (6 novel and 29 known) in 21 IRD-associated genes were identified in 71% of probands (39 of the 55 families). Three families showed phenotypes different from the typically reported clinical findings associated with the causative genes. To our knowledge, this is the largest genetic analysis of IRDs in the Jordanian population to date. Our study also confirms that WES is a powerful tool for the molecular diagnosis of IRDs in large patient cohorts.

Rapid and Progressive Loss of Multiple Retinal Cell Types in Cathepsin D-Deficient Mice-An Animal Model of CLN10 Disease

Vision loss is among the characteristic symptoms of neuronal ceroid lipofuscinosis (NCL), a fatal neurodegenerative lysosomal storage disorder. Here, we performed an in-depth analysis of retinal degeneration at the molecular and cellular levels in mice lacking the lysosomal aspartyl protease cathepsin D, an animal model of congenital CLN10 disease. We observed an early-onset accumulation of storage material as indicated by elevated levels of saposin D and subunit C of the mitochondrial ATP synthase. The accumulation of storage material was accompanied by reactive astrogliosis and microgliosis, elevated expression of the autophagy marker sequestosome 1/p62 and a dysregulated expression of several lysosomal proteins. The number of cone photoreceptor cells was reduced as early as at postnatal day 5. At the end stage of the disease, the outer nuclear layer was almost atrophied, and all cones were lost. A significant loss of rod and cone bipolar cells, amacrine cells and ganglion cells was found at advanced stages of the disease. Results demonstrate that cathepsin D deficiency results in an early-onset and rapidly progressing retinal dystrophy that involves all retinal cell types. Data of the present study will serve as a reference for studies aimed at developing treatments for retinal degeneration in CLN10 disease.

A human model of Batten disease shows role of CLN3 in phagocytosis at the photoreceptor-RPE interface

Mutations in CLN3 lead to photoreceptor cell loss in CLN3 disease, a lysosomal storage disorder characterized by childhood-onset vision loss, neurological impairment, and premature death. However, how CLN3 mutations cause photoreceptor cell death is not known. Here, we show that CLN3 is required for phagocytosis of photoreceptor outer segment (POS) by retinal pigment epithelium (RPE) cells, a cellular process essential for photoreceptor survival. Specifically, a proportion of CLN3 in human, mouse, and iPSC-RPE cells localized to RPE microvilli, the site of POS phagocytosis. Furthermore, patient-derived CLN3 disease iPSC-RPE cells showed decreased RPE microvilli density and reduced POS binding and ingestion. Notably, POS phagocytosis defect in CLN3 disease iPSC-RPE cells could be rescued by wild-type CLN3 gene supplementation. Altogether, these results illustrate a novel role of CLN3 in regulating POS phagocytosis and suggest a contribution of primary RPE dysfunction for photoreceptor cell loss in CLN3 disease that can be targeted by gene therapy.

Gene correction of the CLN3 c.175G>A variant in patient-derived induced pluripotent stem cells prevents pathological changes in retinal organoids

Background

Mutations in CLN3 cause Batten disease, however non‐syndromic CLN3 disease, characterized by retinal‐specific degeneration, has been also described. Here, we characterized an induced pluripotent stem cell (iPSC)‐derived disease model derived from a patient with non‐syndromic CLN3‐associated retinopathy.

Methods

Patient‐iPSC, carrying the 1 kb‐deletion and c.175G>A variants in CLN3, coisogenic iPSC, in which the c.175G>A variant was corrected, and control iPSC were differentiated into neural retinal organoids (NRO) and cardiomyocytes. CLN3 transcripts were analyzed by Sanger sequencing. Gene expression was characterized by qPCR and western blotting. NRO were characterized by immunostaining and electron microscopy.

Results

Novel CLN3 transcripts were detected in adult human retina and control‐NRO. The major transcript detected in patient‐NRO displayed skipping of exons 2 and 4–9. Accumulation of subunit‐C of mitochondrial ATPase (SCMAS) protein was demonstrated in patient‐derived cells. Photoreceptor progenitor cells in patient‐NRO displayed accumulation of peroxisomes and vacuolization of inner segments. Correction of the c.175G>A variant restored CLN3 mRNA and protein expression and prevented SCMAS and inner segment vacuolization.

Conclusion

Our results demonstrate the expression of novel CLN3 transcripts in human retinal tissues. The c.175G>A variant alters splicing of the CLN3 pre‐mRNA, leading to features consistent with CLN3 deficiency, which were prevented by gene correction.

Deep learning segmentation of hyperautofluorescent fleck lesions in Stargardt disease

Stargardt disease is one of the most common forms of inherited retinal disease and leads to permanent vision loss. A diagnostic feature of the disease is retinal flecks, which appear hyperautofluorescent in fundus autofluorescence (FAF) imaging. The size and number of these flecks increase with disease progression. Manual segmentation of flecks allows monitoring of disease, but is time-consuming. Herein, we have developed and validated a deep learning approach for segmenting these Stargardt flecks (1750 training and 100 validation FAF patches from 37 eyes with Stargardt disease). Testing was done in 10 separate Stargardt FAF images and we observed a good overall agreement between manual and deep learning in both fleck count and fleck area. Longitudinal data were available in both eyes from 6 patients (average total follow-up time 4.2 years), with both manual and deep learning segmentation performed on all (n = 82) images. Both methods detected a similar upward trend in fleck number and area over time. In conclusion, we demonstrated the feasibility of utilizing deep learning to segment and quantify FAF lesions, laying the foundation for future studies using fleck parameters as a trial endpoint.

Gene Therapy Targeting the Inner Retina Rescues the Retinal Phenotype in a Mouse Model of CLN3 Batten Disease

The neuronal ceroid lipofuscinoses (NCLs), often referred to as Batten disease, are inherited lysosomal storage disorders that represent the most common neurodegeneration during childhood. Symptoms include seizures, vision loss, motor and cognitive decline, and premature death. The development of brain-directed treatments for NCLs has made noteworthy progress in recent years. Clinical trials are currently ongoing or planned for different forms of the disease. Despite these promising advances, it is unlikely that therapeutic interventions targeting the brain will prevent loss of vision in patients as retinal cells remain untreated and will continue to degenerate. Here, we demonstrate that Cln3^Δex7/8 mice, a mouse model of CLN3 Batten disease with juvenile onset, suffer from a decline in inner retinal function resulting from the death of rod bipolar cells, interneurons vital for signal transmission from photoreceptors to ganglion cells in the retina. We also show that this ocular phenotype can be treated by adeno-associated virus (AAV)-mediated expression of CLN3 in cells of the inner retina, leading to significant survival of bipolar cells and preserved retinal function. In contrast, the treatment of photoreceptors, which are lost in patients at late disease stages, was not therapeutic in Cln3^Δex7/8 mice, underlining the notion that CLN3 disease is primarily a disease of the inner retina with secondary changes in the outer retina. These data indicate that bipolar cells play a central role in this disease and identify this cell type as an important target for ocular AAV-based gene therapies for CLN3 disease.

Loss of CLN3, the gene mutated in juvenile neuronal ceroid lipofuscinosis, leads to metabolic impairment and autophagy induction in retinal pigment epithelium

Juvenile neuronal ceroid lipofuscinosis (JNCL, aka. juvenile Batten disease or CLN3 disease) is a lysosomal storage disease characterized by progressive blindness, seizures, cognitive and motor failures, and premature death. JNCL is caused by mutations in the Ceroid Lipofuscinosis, Neuronal 3 (CLN3) gene, whose function is unclear. Although traditionally considered a neurodegenerative disease, CLN3 disease displays eye-specific effects: Vision loss not only is often one of the earliest symptoms of JNCL, but also has been reported in non-syndromic CLN3 disease. Here we described the roles of CLN3 protein in maintaining healthy retinal pigment epithelium (RPE) and normal vision. Using electroretinogram, fundoscopy and microscopy, we showed impaired visual function, retinal autofluorescent lesions, and RPE disintegration and metaplasia/hyperplasia in a Cln3 ~ 1 kb-deletion mouse model [1] on C57BL/6J background. Utilizing a combination of biochemical analyses, RNA-Seq, Seahorse XF bioenergetic analysis, and Stable Isotope Resolved Metabolomics (SIRM), we further demonstrated that loss of CLN3 increased autophagic flux, suppressed mTORC1 and Akt activities, enhanced AMPK activity, and up-regulated gene expression of the autophagy-lysosomal system in RPE-1 cells, suggesting autophagy induction. This CLN3 deficiency induced autophagy induction coincided with decreased mitochondrial oxygen consumption, glycolysis, the tricarboxylic acid (TCA) cycle, and ATP production. We also reported for the first time that loss of CLN3 led to glycogen accumulation despite of impaired glycogen synthesis. Our comprehensive analyses shed light on how loss of CLN3 affect autophagy and metabolism. This work suggests possible links among metabolic impairment, autophagy induction and lysosomal storage, as well as between RPE atrophy/degeneration and vision loss in JNCL.

Novel homozygous CLN3 missense variant in isolated retinal dystrophy: A case report and electron microscopic findings

Background

Biallelic CLN3 gene variants have been found in either juvenile‐onset neuronal ceroid lipofuscinosis (JNCL) or isolated retinal dystrophy. It has been reported that most JNCL patients carry a common 1.02‐kb deletion variant homozygously. Clinical characteristics of patients with biallelic CLN3 missense variants are not well elucidated.

Methods

We described a 26‐year‐old Japanese male patient with isolated retinal dystrophy. Whole‐exome sequencing (WES) and transmission electron microscopy (TEM) were performed.

Results

Whole‐exome sequencing identified a novel homozygous CLN3 missense variant [c.482C>T; p.(Ser161Leu)]. Ophthalmoscopy revealed retinal degeneration and macular atrophy, and later attenuated retinal vessels. Severely reduced responses were observed in both rod and cone electroretinograms. In TEM of the patient's lymphocytes, fingerprint profiles, which are specific findings in CLN3‐associated JNCL, were observed in 16/624 (2.56%) lymphocytes of the patient, who has never exhibited neurological signs during the 13‐year follow‐up period.

Conclusion

Our results indicated that this novel CLN3 missense variant is associated with teenage‐onset isolated retinal dystrophy. This is the first report of any patient with CLN3‐associated disorder in the Japanese population. Although fingerprint profiles have never been reported in CLN3‐associated isolated retinal dystrophy, these profiles were observed, albeit infrequently, suggesting that frequency of the fingerprint profiles might depend on variant types.

Eye involvement in inherited metabolic disorders

Inherited metabolic disorders are a large group of rare disorders affecting normal biochemical pathways. Many metabolic disorders can present with symptoms affecting the eye, and eye disorders can evolve later in the natural history of an already diagnosed metabolic disorder. The ophthalmic involvement can be very varied affecting any part of the eye, including abnormalities of cornea, lens dislocation and cataracts, retina and the distal optic pathway, and extraocular muscles. Awareness of inherited metabolic disorders is important to facilitate early diagnosis and in some cases instigate early treatment if a patient presents with eye involvement suggestive of a metabolic disorder. Ophthalmological interventions are also an important component of the multisystem holistic approach to treating patients with metabolic disorders.