The Italian reappraisal of the most frequent genetic defects in hereditary optic neuropathies and the global top 10

Clinical and genetic landscape of optic atrophy in 826 families: insights from 50 nuclear genes

Hereditary optic neuropathies (HON) comprise a group of diseases caused by genetic defects in either the mitochondrial or nuclear genomes. The increasing availability of genetic testing has expanded the genetic and phenotypic spectrum of HON more broadly than previously recognized. The genetic and phenotypic landscape of HON is attributed to 50 nuclear genes, so we genetically analysed patients with suspected HON from a group of 4776 index cases following our previous study on 1516 probands with Leber's HON (LHON) who had mitochondrial DNA variants. Exome sequencing was performed in 473 probands diagnosed with nuclear gene-related HON (nHON) and 353 cases with unsolved LHON. Sequencing and variant interpretation of the 50 nuclear genes indicated that the diagnostic yield of exome sequencing for nHON was 31.50% (149/473), while it was markedly lower [1.42% (5/353)] for LHON patients without primary mtDNA mutations. The top five genes implicated in nHON in our in-house cohort were OPA1, WFS1, FDXR, ACO2 and AFG3L2, which accounted for 82.46% of probands. Although OPA1 was the most prevalent nHON-causative gene in both our cohort (53.25%) and a literature review (37.09%), the predominance of OPA1, WFS1 and FDXR differed significantly between our in-house cohort and the literature review (P-adjusted < 0.001). Fundus changes in nHON could be stratified into three categories: the most common was optic atrophy at examination (78.79%); the rarest was LHON-like optic atrophy (3.64%); and optic atrophy with concurrent retinal degeneration (17.57%), an independent risk factor for visual prognosis in nHON, occurred at an intermediate frequency. A systematic genotype-phenotype analysis highlighted different genetic contributions for ocular, extraocular neurological and extraocular non-neurological phenotypes. In addition, systemic variant analysis at the individual gene level suggested a revised interpretation of the pathogenicity of a WFS1 heterozygous truncation variant. This study provides a panoramic view of the genetic and phenotypic profiles of HON in a real-world study and the literature. The categories of nHON fundus phenotypes will benefit future studies on the molecular mechanisms underlying HON and targeted therapies. In addition to routine ophthalmic examinations, careful examination of extraocular symptoms and meaningful genetic counselling are warranted for patients with nHON.

Mutation of CRYAB encoding a conserved mitochondrial chaperone and antiapoptotic protein causes hereditary optic atrophy

The degeneration of retinal ganglion cells (RGC) due to mitochondrial dysfunctions manifests optic neuropathy. However, the molecular components of RGC linked to optic neuropathy manifestations remain largely unknown. Here, we identified a potentially novel optic atrophy-causative CRYAB gene encoding a highly conserved major lens protein acting as mitochondrial chaperone and possessing antiapoptotic activities. The heterozygous CRYAB mutation (c.313G>A, p. Glu105Lys) was cosegregated with autosomal dominant inheritance of optic atrophy in 3 Chinese families. The p.E105K mutation altered the structure and function of CRYAB, including decreased stability, reduced formation of oligomers, and decreased chaperone activity. Coimmunoprecipitation indicated that the p.E105K mutation reduced the interaction of CRYAB with apoptosis-associated cytochrome c and voltage-dependent anion channel protein. The cell lines carrying the p.E105K mutation displayed promotion of apoptosis and defective assembly, stability, and activities of oxidative phosphorylation system as well as imbalance of mitochondrial dynamics. Involvement of CRYAB in optic atrophy was confirmed by phenotypic evaluations of Cryabp.E105K-knockin mice. These mutant mice exhibited ocular lesions that included alteration of intraretinal layers, degeneration of RGCs, photoreceptor deficits, and abnormal retinal vasculature. Furthermore, Cryab-deficient mice displayed elevated apoptosis and mitochondrial dysfunctions. Our findings provide insight of pathophysiology of optic atrophy arising from RGC degeneration caused by CRYAB deficiency-induced elevated apoptosis and mitochondrial dysfunctions.

Mitochondrial retinopathies and optic neuropathies: The impact of retinal imaging on modern understanding of pathogenesis, diagnosis, and management

Advancements in ocular imaging have significantly broadened our comprehension of mitochondrial retinopathies and optic neuropathies by examining the structural and pathological aspects of the retina and optic nerve in these conditions. This article aims to review the prominent imaging characteristics associated with mitochondrial retinopathies and optic neuropathies, aiming to deepen our insight into their pathogenesis and clinical features. Preceding this exploration, the article provides a detailed overview of the crucial genetic and clinical features, which is essential for the proper interpretation of in vivo imaging. More importantly, we will provide a critical analysis on how these imaging modalities could serve as biomarkers for characterization and monitoring, as well as in guiding treatment decisions. However, these imaging methods have limitations, which will be discussed along with potential strategies to mitigate them. Lastly, the article will emphasize the potential advantages and future integration of imaging techniques in evaluating patients with mitochondrial eye disorders, considering the prospects of emerging gene therapies.

Mitochondrial DNA mutations in Korean patients with Leber's hereditary optic neuropathy

In order to explore the spectrum of mitochondrial DNA (mtDNA) mutations in Korean patients with Leber's hereditary optic neuropathy (LHON), we investigated the spectrum of mtDNA mutations in 145 Korean probands confirmed with the diagnosis of LHON. Total genomic DNA was isolated from the peripheral blood leukocytes of the patients with suspected LHON, and mtDNA mutations were identified by direct sequencing. Analysis of mtDNA mutations revealed seven primary LHON mutations including the nucleotide positions (nps) 11778A (101 probands, 69.2%), 14484C (31 probands, 21.2%), 3460A (5 probands, 3.4%), and G3635A, G3733A, C4171A, and G13051A mutations in one proband each. In addition, two provisional mtDNA mutations at nps T3472C, and G13259A were each found in one proband, respectively. Another provisional mtDNA mutation at np T3394C was found in two probands. In conclusion, the spectrum of mtDNA mutations in Korean patients with LHON may differ from other ethnicities, which is characterized by high prevalence of 11778A and 14484C mutations, and a low prevalence of the 3460A mutation.