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