Early photoreceptor outer segment loss and retinoschisis in Cohen syndrome

A rare canonical splice-site variant in VPS13B causes attenuated Cohen syndrome

BACKGROUND

To describe a patient with a history of obesity, retinal dystrophy, type II diabetes, and mild cognitive impairment; found to harbour biallelic splice-site variants in VPS13B.

MATERIALS & METHODS

A complete ophthalmic evaluation was performed at Moorfields Eye Hospital (London, United Kingdom), consisting of measurement of best-corrected visual acuity (BCVA), slit lamp and dilated fundus evaluation, colour, autofluorescence and near-infrared retinal imaging, spectral domain-optical coherence tomography, and electroretinogram (ERG). Whole-genome sequencing was performed as part of the UK's 100,000 Genomes Project.

RESULTS

A 26-year-old Pakistani man with normal appearance, stature, and head size presented with decreased BCVA and severely constricted visual fields to our Ophthalmic Genetics clinic. He had a history of obesity, type II diabetes, and mild cognitive impairment. His evaluation showed retina-wide, severe photoreceptor dysfunction in both eyes, with undetectable scotopic and photopic ERG waveforms. Genomic analysis identified a homozygous rare splice donor variant in the VPS13B gene (c.5024+2T>C) that was demonstrated to lead to skipping of the in-frame exon 31 (p.Gln1607_Ser1675delinsHis).

CONCLUSIONS

Exon 31 skipping in VPS13B may lead to a hypomorphic change, with partial gene function and an incomplete, mild Cohen syndrome-like phenotype.

Cystoid maculopathy is a frequent feature of Cohen syndrome-associated retinopathy

Cohen syndrome (CS) is a rare syndromic form of rod-cone dystrophy. Recent case reports have suggested that cystoid maculopathy (CM) could affect CS patients with an early onset and high prevalence. Our study aims at improving our understanding and management of CM in CS patients through a retrospective case series of ten CS patients with identified pathogenic variants in VPS13B. Longitudinal optical coherence tomography (OCT) imaging was performed and treatment with carbonic anhydrase inhibitors (CAI) was provided to reduce the volume of cystoid spaces. CM affected eight out of ten patients in our cohort. The youngest patient showed a strong progression of macular cysts from the age of 4.5 to 5 years despite oral CAI medication. Other teenage and young adult patients showed stable macular cysts with and without treatment. One patient showed a moderate decrease of cystoid spaces in the absence of treatment at 22 years of age. Through a correlative analysis we found that the volume of cystoid spaces was positively correlated to the thickness of peripheral and macular photoreceptor-related layers. This study suggests that CAI treatments may not suffice to improve CM in CS patients, and that CM may resolve spontaneously during adulthood as photoreceptor dystrophy progresses.

Resolution of cystoid macular edema with topical carbonic anhydrase inhibitor in a patient with retinal dystrophy associated with Cohen syndrome

Background: Cohen Syndrome (CS) is an autosomal recessive multisystemic disorder characterized by various ophthalmologic findings, including retinal dystrophy and associated cystoid macular edema (CME), in which there was no known effective treatment approach.Material and Methods: We describe a CS patient with a homozygous c.62 T > G, p.(Leu21*) mutation in the VPS13B gene with a topical carbonic anhydrase inhibitor (CAI; brinzolamide %1, thrice daily) responding CME.Case Description: A seven-year-old girl with an established diagnosis of CS was referred with a primary complaint of nyctalopia. On ophthalmologic examination, bilateral decreased visual acuity and normal-appearing macula with mild optic disc pallor were present. However, the detailed evaluation revealed bilateral blunted foveal reflexes, barely visible foveal pigmentation, and slightly attenuated retinal vessels without any peripheral retinal pigmentary changes in dilated fundus examination, and CME on optical coherence tomography. Bilateral topical brinzolamide thrice daily was initiated for CME. Visual acuity increased, and CME was resolved except for minimal schisis at the inner nuclear layer level at the third-month follow-up visit and remained stable up to one-year follow-up. CME reappeared after five months of self-discontinuation of the patient's therapy but resolved again with treatment resumption.Conclusion: We report the first case of CME secondary to rod-cone dystrophy associated with CS showing improvement in anatomy and visual acuity with a topical CAI.

Cohen Syndrome-Associated Cataract Is Explained by VPS13B Functions in Lens Homeostasis and Is Modified by Additional Genetic Factors

Purpose

Cohen syndrome (CS) is a rare genetic disorder caused by variants of the VPS13B gene. CS patients are affected with a severe form of retinal dystrophy, and in several cases cataracts also develop. The purpose of this study was to investigate the mechanisms and risk factors for cataract in CS, as well as to report on cataract surgeries in CS patients.

Methods

To understand how VPS13B is associated with visual impairments in CS, we generated the Vps13b^{∆Ex3/∆Ex3} mouse model. Mice from 1 to 3 months of age were followed by ophthalmoscopy and slit-lamp examinations. Phenotypes were investigated by histology, immunohistochemistry, and western blot. Literature analysis was performed to determine specific characteristic features of cataract in CS and to identify potential genotype–phenotype correlations.

Results

Cataracts rapidly developed in 2-month-old knockout mice and were present in almost all lenses at 3 months. Eye fundi appeared normal until cataract development. Lens immunostaining revealed that cataract formation was associated with the appearance of large vacuoles in the cortical area, epithelial–mesenchymal transition, and fibrosis. In later stages, cataracts became hypermature, leading to profound retinal remodeling due to inflammatory events. Literature analysis showed that CS-related cataracts display specific features compared to other forms of retinitis pigmentosa-related cataracts, and their onset is modified by additional genetic factors. Corroboratively, we were able to isolate a subline of the Vps13b^{∆Ex3/∆Ex3} model with delayed cataract onset.

Conclusions

VPS13B participates in lens homeostasis, and the CS-related cataract development dynamic is linked to additional genetic factors.

Coexistence of bilateral macular edema and pale optic disc in the patient with Cohen syndrome

Background

Cohen syndrome (Q87.8;ORPHA:193; OMIM#216550) is an autosomal recessive inherited genetic disorder caused by mutation in the VPS13B/COH1 gene. It is characterized by variable clinical symptoms such as deformity of the head, face, hands and feet, eye abnormalities, abdominal obesity, neutropenia and nonprogressive intellectual disability. The typical lesions in the eyeball in Cohen syndrome include high myopia, retinal dystrophy, strabismus, maculopathy and lens subluxation. The present study describes the coexistence of bilateral macular edema with pale optic disc in a patient with a homozygous deletion in the VPS13B/COH1 gene.

Material and methods

A 6-year-old Caucasian girl with facial dysmorphism, microcephaly, prominent upper incisors, narrow hands with slender fingers, congenital heart defect and ophthalmic symptoms was subjected to genetic testing. The genetic evaluation revealed a homozygous deletion on the long arm of chromosome 8 encompassing 20-25 exons of the VPS13 gene, as confirmed by Cohen syndrome. She underwent a full ophthalmological examination with the assessment of slit lamp examination of anterior segment and fundoscopy, refraction error, biometry, central corneal thickness and additionally electroretinography, optical coherence tomography and fundus photography.

Results

In the ophthalmologic examination, the girl had bilateral astigmatism accompanied by myopia and a marked reduction in central corneal thickness. Fundus examination showed pale optic nerve discs and "salt and pepper" retinopathy. Bilateral cystic macular edema was revealed in handheld optical coherence tomography. Electroretinography showed a reduced response amplitude of cones and rods.

Conclusion

In a patient with high myopia, macular edema, pale optic disc and facial dysmorphism, Cohen syndrome should be considered in the differential diagnosis. The severity of individual clinical features in patients with Cohen syndrome varies. It can be assumed that the type of mutation affects the occurrence and severity of individual symptoms.

Optical coherence tomography findings in Cohen syndrome

Cohen syndrome is a rare disease that causes myopia and retinal degeneration in the setting of developmental delay and characteristic craniofacial features. We report optical coherence tomography (OCT) abnormalities in 4 patients with Cohen syndrome, 2 of whom have longitudinal follow-up. All subjects had schisis-like changes, with cystoid spaces in the inner retina as well as diffuse outer retinal atrophy sparing the subfoveal region. Ophthalmologic findings in 1 patient led to the work-up that resulted in a diagnosis of Cohen syndrome, suggesting that characteristic retinal abnormalities visualized by fundus examination and OCT may represent distinguishing features of this syndrome.

NMNAT1-ASSOCIATED CONE-ROD DYSTROPHY: EVIDENCE FOR A SPECTRUM OF FOVEAL MALDEVELOPMENT

PURPOSE

To describe in detail the phenotype of two siblings with biallelic NMNAT1 mutations.

METHODS

A 4-year-old male patient (P1) and his 7-year-old sister (P2), product of a nonconsanguineous union of Egyptian ancestry, underwent a comprehensive ophthalmic examination, retinal imaging with spectral domain optical coherence tomography and near infrared (NIR) fundus autofluorescence (FAF), and full-field electroretinograms (ERG).

RESULTS

Patients had blurred vision and nystagmus at ∼3 years of age. P2 was hyperopic (+6D). Visual acuity in P1 was 20/100 at age 3 and remained at ∼20/125 at age 4; P2 visual acuity was 20/70 at age 4 and declined to ∼20/200 at age 7. ERGs recorded in P1 showed relatively large rod-mediated responses but nearly undetectable cone signals. There was foveal/parafoveal depigmentation. Spectral domain optical coherence tomography showed hypoplastic foveas, a thin outer nuclear layer centrally but normal thickness beyond the vascular arcades. At the foveal center, cone outer segments were absent and the outer nuclear layer was further hyporreflective. The inner retina was mostly within normal limits. There was central depigmentation on near infrared fundus autofluorescence. Biallelic mutations were identified in NMNAT1: One was previously reported (c.769 G>A; pGlu257Lys), and the other one (c.245T>C; pVal82Ala) was novel.

CONCLUSION

NMNAT1 mutations cause a consistent phenotype characterized by early-onset, progressive, cone>rod retinawide dysfunction and predominantly central abnormalities ranging from a hypoplastic to an atrophic fovea, supporting a critical role for NMNAT1 in central retinal development and maintenance. Relatively preserved inner retina and detectable photoreceptors may become therapeutic targets.

CDG and immune response: From bedside to bench and back

Glycosylation is an essential biological process that adds structural and functional diversity to cells and molecules, participating in physiological processes such as immunity. The immune response is driven and modulated by protein-attached glycans that mediate cell-cell interactions, pathogen recognition and cell activation. Therefore, abnormal glycosylation can be associated with deranged immune responses. Within human diseases presenting immunological defects are congenital disorders of glycosylation (CDG), a family of around 130 rare and complex genetic diseases. In this review, we have identified 23 CDG with immunological involvement, characterized by an increased propensity to-often life-threatening-infection. Inflammatory and autoimmune complications were found in 7 CDG types. CDG natural history(ies) and the mechanisms behind the immunological anomalies are still poorly understood. However, in some cases, alterations in pathogen recognition and intracellular signaling (eg, TGF-β1, NFAT, and NF-κB) have been suggested. Targeted therapies to restore immune defects are only available for PGM3-CDG and SLC35C1-CDG. Fostering research on glycoimmunology may elucidate the involved pathophysiological mechanisms and open new therapeutic avenues, thus improving CDG patients' quality of life.