Variants in UBAP1L lead to autosomal recessive rod-cone and cone-rod dystrophy.

PURPOSE: Progressive inherited retinal degenerations (IRDs) affecting rods and cones are clinically and genetically heterogeneous and can lead to blindness with limited therapeutic options. The major gene defects have been identified in subjects of European and Asian descent with only few reports of North African descent. METHODS: Genome, targeted next-generation, and Sanger sequencing was applied to cohort of ∼4000 IRDs cases. Expression analyses were performed including Chip-seq database analyses, on human-derived retinal organoids (ROs), retinal pigment epithelium cells, and zebrafish. Variants' pathogenicity was accessed using 3D-modeling and/or ROs. RESULTS: Here, we identified a novel gene defect with three distinct pathogenic variants in UBAP1L in 4 independent autosomal recessive IRD cases from Tunisia. UBAP1L is expressed in the retinal pigment epithelium and retina, specifically in rods and cones, in line with the phenotype. It encodes Ubiquitin-associated protein 1-like, containing a solenoid of overlapping ubiquitin-associated domain, predicted to interact with ubiquitin. In silico and in vitro studies, including 3D-modeling and ROs revealed that the solenoid of overlapping ubiquitin-associated domain is truncated and thus ubiquitin binding most likely abolished secondary to all variants identified herein. CONCLUSION: Biallelic UBAP1L variants are a novel cause of IRDs, most likely enriched in the North African population.

DEEP PHENOTYPING AND FURTHER INSIGHTS INTO ITM2B-RELATED RETINAL DYSTROPHY.

PURPOSE: To reappraise the presentation and the course of ITM2B-related retinal dystrophy and give further insights into ITM2B expression in the retina. METHODS: The clinical data of nine subjects with ITM2B-related retinal dystrophy were retrospectively reviewed. The genetic mutation was assessed for its influence on splicing in cultured fibroblasts. The cellular expression of ITM2B within the inner retina was investigated in wild-type mice through mRNA in situ hybridization. RESULTS: All patients complained of decreased vision and mild photophobia around their twenties-thirties. The peculiar feature was the hyperreflective material on optical coherence tomography within the inner retina and the central outer nuclear layer with thinning of the retinal nerve fiber layer. Although retinal imaging revealed very mild or no changes over the years, the visual acuity slowly decreased with about one Early Treatment Diabetic Retinopathy Study letter per year. Finally, full-field electroretinography showed a mildly progressive inner retinal and cone dysfunction. ITM2B mRNA is expressed in all cellular types of the inner retina. Disease mechanism most likely involves mutant protein misfolding and/or modified protein interaction rather than misplicing. CONCLUSION: ITM2B-related retinal dystrophy is a peculiar, rare, slowly progressive retinal degeneration. Functional examinations (full-field electroretinography and visual acuity) seem more accurate in monitoring the progression in these patients because imaging tends to be stable over the years.

Generation of human induced pluripotent stem cell lines from a subject with UBAP1L-associated retinal dystrophy and CRISPR/cas9-corrected isogenic iPSC lines.

A Human induced pluripotent stem cell (iPSC) line was generated from dermal fibroblasts of a patient affected with an autosomal recessive retinal dystrophy carrying the homozygous c.910-7G>A variant in UBAP1L. Three isogenic control iPSC lines derived from this affected subject line were created using CRISPR/Cas9 engineering. All iPSC lines expressing the pluripotency markers, were able to differentiate into the three germ layers, and exhibit a normal karyotype. These cellular models will provide a powerful tool to study disease mechanisms associated with the recently reported UBAP1L- associated retinal dystrophy and better understand the role of the protein in retinal physiology.

Generation of gene corrected human isogenic iPSC lines (IDVi003-A_CR13, IDVi003-A_CR21, IDVi003-A_CR24) from an inherited retinal dystrophy patient-derived IPSC line ITM2B-5286-3 (IDVi003-A) carrying the ITM2B c.782A > C variant using CRISPR/Cas9.

The ITM2B-related retinal dystrophy (ITM2B-RD) was identified within patients carrying the autosomal dominant variant [c.782A > C, p.(Glu261Ala)] in ITM2B from whom induced pluripotent stem cell (IPSC) lines were previously generated. Here, we report the generation of three isogenic control iPSC lines from the derived affected subject cell line (ITM2B-5286-3) using CRISPR/Cas9 engineering. The three generated lines express pluripotency markers, can be differentiated into the three germ layers and present a normal karyotype. The generated iPSC lines can be used to study the implications of ITM2B-RD variant in vitro.

Generation of human induced pluripotent stem cell lines from a patient with ITM2B-related retinal dystrophy and a non mutated brother.

Human induced pluripotent stem cell (iPSC) lines were generated from fibroblasts of a patient affected with an autosomal dominant retinal dystrophy carrying the mutation c.782A>C, p.Glu261Ala in ITM2B and from an unaffected brother. Three different iPSC lines were generated and characterized from primary dermal fibroblasts of the affected subject and two from the unaffected brother. All iPSC lines expressed the pluripotency markers, were able to differentiate into the three germ layers and presented normal karyotypes. This cellular model will provide a powerful tool to study this retinal dystrophy and better understand the role of ITM2B.