Laurence Pierrache

Whole-Exome Sequencing Identifies Biallelic IDH3A Variants as a Cause of Retinitis Pigmentosa Accompanied by Pseudocoloboma

PURPOSE To identify the genetic cause of and describe the phenotype in 4 families with autosomal recessive retinitis pigmentosa (arRP) that can be associated with pseudocoloboma. DESIGN Case series. PARTICIPANTS Seven patients from 4 unrelated families with arRP, among whom 3 patients had bilateral early-onset macular pseudocoloboma. METHODS We performed homozygosity mapping and whole-exome sequencing in 5 probands and 2 unaffected family members from 4 unrelated families. Subsequently, Sanger sequencing and segregation analysis were performed in additional family members. We reviewed the medical history of individuals carrying IDH3A variants and performed additional ophthalmic examinations, including full-field electroretinography, fundus photography, fundus autofluorescence imaging, and optical coherence tomography. MAIN OUTCOME MEASURES IDH3A variants, age at diagnosis, visual acuity, fundus appearance, visual field, and full-field electroretinography, fundus autofluorescence, and optical coherence tomography findings. RESULTS We identified 7 different variants in IDH3A in 4 unrelated families, that is, 5 missense, 1 nonsense, and 1 frameshift variant. All participants showed symptoms early in life, ranging from night blindness to decreased visual acuity, and were diagnosed between the ages of 1 and 11 years. Four participants with biallelic IDH3A variants displayed a typical arRP phenotype and 3 participants were diagnosed with arRP and pseudocoloboma of the macula. CONCLUSIONS IDH3A variants were identified as a novel cause of typical arRP in some individuals associated with macular pseudocoloboma. We observed both phenotypes in 2 siblings carrying the same compound heterozygous variants, which could be explained by variable disease expression and warrants caution when making assertions about genotype-phenotype correlations.

Mutations in AGBL5, Encoding alpha-Tubulin Deglutamylase, Are Associated With Autosomal Recessive Retinitis Pigmentosa

Purpose AGBL5, encoding ATP/GTP binding protein-like 5, was previously proposed as an autosomal recessive retinitis pigmentosa (arRP) candidate gene based on the identification of missense variants in two families. In this study, we performed next-generation sequencing to reveal additional RP cases with AGBL5 variants, including protein-truncating variants. Methods Whole-genome sequencing (WGS) or whole-exome sequencing (WES) was performed in three probands. Subsequent Sanger sequencing and segregation analysis were performed in the selected candidate genes. The medical history of individuals carrying AGBL5 variants was reviewed and additional ophthalmic examinations were performed, including fundus photography, fundus autofluorescence imaging, and optical coherence tomography. Results AGBL5 variants were identified in three unrelated arRP families, comprising homozygous variants in family 1 (c.1775G>A:p.(Trp592*)) and family 2 (complex allele: c.[323C>G; 2659T>C]; p.[(Pro108Arg; *887Argext*1)]), and compound heterozygous variants (c.752T>G:p.(Val251Gly) and c.1504dupG:p.(Ala502Glyfs*15)) in family 3. All affected individuals displayed typical RP phenotypes. Conclusions Our study convincingly shows that variants in AGBL5 are associated with arRP. The identification of AGBL5 and TTLL5, a previously described RP-associated gene encoding the tubulin tyrosine ligase-like family, member 5 protein, highlights the importance of poly- and deglutamylation in retinal homeostasis. Further studies are required to investigate the underlying disease mechanism associated with AGBL5 variants.

Method for segmentation of the layers in the outer retina

This paper presents a method to determine the number of visible layers in the outer retina and perform segmentation. Each layer in the outer retina is represented by a Gaussian function, and multiple models with a different number of layers are used to form the outer retina. Parameters of competing models are calculated by using maximum likelihood estimation after which the model that best describes the data is selected. Model selection is based on the goodness of fit and model complexity thereby ensuring that the model that best represents the data is chosen. The method was applied to in-vivo macular images of human retinas acquired by optical coherence tomography after conversion to attenuation coefficients. Examples of detected number of visible layers and corresponding segmentation results are shown in both normal and retinitis pigmentosa affected retinas.

Antisense Oligonucleotide-Based Splicing Correction in Individuals with Leber Congenital Amaurosis due to Compound Heterozygosity for the c.2991+1655A>G Mutation in CEP290

Leber congenital amaurosis (LCA) is a rare inherited retinal disorder affecting approximately 1:50,000 people worldwide. So far, mutations in 25 genes have been associated with LCA, with CEP290 (encoding the Centrosomal protein of 290 kDa) being the most frequently mutated gene. The most recurrent LCA-causing CEP290 mutation, c.2991+1655A>G, causes the insertion of a pseudoexon into a variable proportion of CEP290 transcripts. We previously demonstrated that antisense oligonucleotides (AONs) have a high therapeutic potential for patients homozygously harbouring this mutation, although to date, it is unclear whether rescuing one single allele is enough to restore CEP290 function. Here, we assessed the AON efficacy at RNA, protein and cellular levels in samples that are compound heterozygous for this mutation, together with a protein-truncating mutation in CEP290. We demonstrate that AONs can efficiently restore splicing and increase protein levels. However, due to a high variability in ciliation among the patient-derived cell lines, the efficacy of the AONs was more difficult to assess at the cellular level. This observation points towards the importance of the severity of the second allele and possibly other genetic variants present in each individual. Overall, AONs seem to be a promising tool to treat CEP290-associated LCA, not only in homozygous but also in compound heterozygous carriers of the c.2991+1655A>G variant.