Ceramide synthase TLCD3B as a novel gene associated with human recessive cone-rod dystrophy and maculopathy

Abstract

Purpose : Inherited retinal dystrophy (IRD) is a genetically heterogeneous group of diseases resulting in irreversible vision loss. Identification and functional studies to understand the underlying molecular causes of IRD are important for patient diagnosis and therapy development. Our study aims at identifying novel IRD associated genes through a combination of next generation sequencing and animal model studies.

Methods : Patients were recruited from the inherited retinal disorders clinic. Clinical data included best-corrected visual acuity, fundus autofluorescence, optical coherence tomography, and full-field electroretinography (ERG). Candidate variants in TLCD3B identified by NGS were investigated. RNA-sequencing data was obtained from dbGap for expression analysis of ceramide synthases. The retinal function in Tlcd3b^KO/KO mice was assessed by ERG performed at 7-months. The murine retinal cross-sections were stained with Hematoxylin and eosin (H&E) and immunofluorescent staining was performed on retinal whole mounts to assess the cone photoreceptors.

Results : Novel homozygous mutations in TLCD3B were identified in four patients from three unrelated families diagnosed with cone-rod dystrophy (CRD) with or without maculopathy, providing the first link between TLCD3B and IRD. All patients presented with progressive central vision loss and macular atrophy. Full-field ERG abnormalities were either confined to photopic recordings or showed photopic and scotopic ERG involvement. The retinal function and morphology of Tlcd3b^KO/KO mice showed reduced scotopic and photopic b-wave responses and a 20% reduction of the outer nuclear layer thickness. Immunofluorescent staining revealed a 30% reduction in cone photoreceptors in Tlcd3b^KO/KO mice.

Conclusions : This study is the first to associate mutations in the ceramide gene TLCD3B with CRD and maculopathy in humans. The Tlcd3b^KO/KO mice recapitulate the human peripheral retinal phenotype and can serve as a good model to study the mechanism of degeneration and develop targeted therapies. The Tlcd3b knock out model is the first in vivo model that demonstrates ceramide to be essential for the survival and function of photoreceptor cells.

This is a 2020 ARVO Annual Meeting abstract.