Renal coloboma syndrome/dominant optic atrophy with severe retinal atrophy and de novo digenic mutations in PAX2 and OPA1

Renal coloboma syndrome (RCS) and dominant optic atrophy are mainly caused by heterozygous mutations in PAX2 and OPA1, respectively. We describe a patient with digenic mutations in PAX2 and OPA1. A female infant was born without perinatal abnormalities. Magnetic resonance imaging at 4 months of age showed bilateral microphthalmia and optic nerve hypoplasia. Appropriate body size was present at 2 years of age, and mental development was favorable. Color fundus photography revealed severe retinal atrophy in both eyes. Electroretinography showed slight responses in the right eye, but no responses in the left eye, suggesting a high risk of blindness. Urinalysis results were normal, creatinine-based estimated glomerular filtration rate was 63.5 mL/min/1.73 m2, and ultrasonography showed bilateral hypoplastic kidneys. Whole exome sequencing revealed de novo frameshift mutations in PAX2 and OPA1. Both variants were classified as pathogenic (PVS1, PS2, PM2) based on the guidelines from the American College of Medical Genetics and Genomics (ACMG). Genetic testing for ocular diseases should be considered for patients with suspected RCS and a high risk of total blindness.

Idebenone Treatment in Patients with OPA1-Dominant Optic Atrophy: A Prospective Phase 2 Trial

The aim of this study was to evaluate the therapeutic effect of idebenone in patients with OPA1-dominant optic atrophy (DOA). Sixteen patients with genetically confirmed OPA1-DOA were treated with 900 mg idebenone daily for 12 months. The primary endpoint was the best recovery/least deterioration of visual acuity. Secondary endpoints were the changes of visual acuity, colour vision, contrast sensitivity, visual field, peripapillary retinal nerve fibre layer thickness (pRNFLT), and visual-related quality of life. For the primary endpoint, a significant increase was observed for the right eye (p = .0027), for the left eye (p = .0111) and for the better-seeing eye (p = .0152). For visual fields, a significant improvement was observed for the left eye between baseline and 9 months (p = .0038). Regarding pRNFLT, a significant decrease was found for the left eye between baseline and 3 months (p = .0413) and between baseline and 6 months (p = .0448). In the visual function questionnaire, a significant improvement was observed in the subscale general vision (p = .0156) and in the composite score (p = .0256). In conclusion, best recovery of visual acuity improved, even though the amount of improvement was small. Furthermore, a maintenance of visual function after 12 months of idebenone intake could be observed as well as a significant improvement in vision-related quality of life.Whether this effect is due to idebenone treatment, the placebo effect, or is explainable by the natural progression of DOA, remains unclear. Trial registration: EU Clinical Trials Register, EudraCT Number: 2019-001493-28.

Peripapillary capillary network in dominant optic atrophy linked to OPA1 gene

Peripapillary capillary network using optical coherence tomography angiography (OCT-A) was analysed in two siblings suffering from dominant optic atrophy linked to OPA-1 gene mutation. Peripapillary capillary network has been scarcely described in this type of optic atrophy.

Capturing the experiences of patients with inherited optic neuropathies: a systematic review of patient-reported outcome measures (PROMs) and qualitative studies

PURPOSE

To identify and comprehensively evaluate studies capturing the experience of individuals affected by an inherited optic neuropathy (ION), focusing on patient-reported outcome measures (PROMs) and qualitative studies where the health status and quality of life (QoL) of these individuals have been explored.

METHODS

Systematic review of five databases using a search strategy combining four concepts: (1) ION; (2) QoL and health status; (3) PROMs; and (4) qualitative research. Studies assessing the impact of ION on any QoL domain using a PROM or qualitative methodology were included and appraised, using criteria based on the COSMIN checklist (for PROM studies) and the CASP checklist (for qualitative studies).

RESULTS

Of 1326 unique articles identified, six studies were included. Five PROMs were identified: Visual Function Index (VF-14); Hospital Anxiety and Depression Scale (HADS); a novel graphical online assessment tool (NGOAT) for reporting emotional response to vision loss; a new PROM informed by the DSM-V Criteria for Major Depressive Disorder; and an interpersonal and career 'impact rating' PROM. The psychometric performance of included PROMs were poorly described. Qualitative studies found that vision loss resulted in psychosocial losses including loss of social and communication skills and loss of independence and freedom. Factors that modified the response to vision loss were also identified.

CONCLUSION

The current PROMs used by individuals with ION have poor content coverage, primarily measuring activity limitation and emotional well-being, and insufficient reporting of psychometric performance. There is a need to develop a PROM for individuals ION to report their experiences of living with their condition.

Dominant optic atrophy: Culprit mitochondria in the optic nerve

Dominant optic atrophy (DOA) is an inherited mitochondrial disease leading to specific degeneration of retinal ganglion cells (RGCs), thus compromising transmission of visual information from the retina to the brain. Usually, DOA starts during childhood and evolves to poor vision or legal blindness, affecting the central vision, whilst sparing the peripheral visual field. In 20% of cases, DOA presents as syndromic disorder, with secondary symptoms affecting neuronal and muscular functions. Twenty years ago, we demonstrated that heterozygous mutations in OPA1 are the most frequent molecular cause of DOA. Since then, variants in additional genes, whose functions in many instances converge with those of OPA1, have been identified by next generation sequencing. OPA1 encodes a dynamin-related GTPase imported into mitochondria and located to the inner membrane and intermembrane space. The many OPA1 isoforms, resulting from alternative splicing of three exons, form complex homopolymers that structure mitochondrial cristae, and contribute to fusion of the outer membrane, thus shaping the whole mitochondrial network. Moreover, OPA1 is required for oxidative phosphorylation, maintenance of mitochondrial genome, calcium homeostasis and regulation of apoptosis, thus making OPA1 the Swiss army-knife of mitochondria. Understanding DOA pathophysiology requires the understanding of RGC peculiarities with respect to OPA1 functions. Besides the tremendous energy requirements of RGCs to relay visual information from the eye to the brain, these neurons present unique features related to their differential environments in the retina, and to the anatomical transition occurring at the lamina cribrosa, which parallel major adaptations of mitochondrial physiology and shape, in the pre- and post-laminar segments of the optic nerve. Three DOA mouse models, with different Opa1 mutations, have been generated to study intrinsic mechanisms responsible for RGC degeneration, and these have further revealed secondary symptoms related to mitochondrial dysfunctions, mirroring the more severe syndromic phenotypes seen in a subgroup of patients. Metabolomics analyses of cells, mouse organs and patient plasma mutated for OPA1 revealed new unexpected pathophysiological mechanisms related to mitochondrial dysfunction, and biomarkers correlated quantitatively to the severity of the disease. Here, we review and synthesize these data, and propose different approaches for embracing possible therapies to fulfil the unmet clinical needs of this disease, and provide hope to affected DOA patients.

Microcystic macular degeneration in autosomal hereditary optic neuropathies: A cross-sectional retrospective study

OBJECTIVE

Patients with autosomal optic neuropathies (AON) may develop microcystic macular degeneration (MMD), observed on retinal optical coherence tomography (OCT) examination. This study aimed to report the prevalence of MMD in AON patients and to assess the consequences of MMD on retinal architecture.

METHODS

Retrospective single-center study conducted between 2001 and 2018. Patients affected by AON secondary to OPA1 or WFS1 gene mutations were included. The following data were collected: visual acuity, macular volume, vitreomacular interface and presence or absence of MMD.

RESULTS

Forty-two subjects (34 OPA1, 8 WFS1) were included. MMD was found in 12 (29%) patients, i.e. 6 of the 8 WFS1 patients (75%) and 6 of the 34 OPA1 patients (17%). In cases with MMD, total retinal volume was greater (P=0.02) in accordance with thickening of the inner nuclear layer (P<0.001). WFS1 subjects had the highest total retinal volume (P=0.01), in relation to a thickening of the inner plexiform layer (P=0.02), inner nuclear layer (P<0.001) and outer plexiform layer (P=0.002). MMD was significantly associated with the WFS1 mutation (P<0.001). No significant association was found between the presence of vitreomacular adhesion and MMD.

CONCLUSION

MMD was found in 29% of patients affected by AON and was more frequent in cases with a WFS1 gene mutation. MMD appears to be related to primary ganglion cell degeneration and Müller cell dysfunction. The vitreomacular interface does not appear to play a role in the occurrence of MMD.

Neuro-ophthalmic manifestations of mitochondrial disorders and their management

The visual system has high metabolic requirements and is therefore particularly vulnerable to mitochondrial dysfunction. The most commonly affected tissues include the extraocular muscles, photoreceptors, retinal pigment epithelium, optic nerve and visual cortex. Hence, the most common manifestations of mitochondrial disorders are progressive external ophthalmoplegia, macular pattern dystrophy, pigmentary retinopathy, optic neuropathy and retrochiasmal visual field loss. With the exception of Leber hereditary optic neuropathy and stroke-like episodes seen in mitochondrial encephalopathy, lactic acidosis and stroke-like episodes, the majority of neuro-ophthalmic manifestations have an insidious onset. As such, some patients may not recognize subtle progressive visual symptoms. When mitochondrial disorders are highly suspected, meticulous examination performed by an ophthalmologist with targeted ancillary testing can help confirm the diagnosis. Similarly, neuro-ophthalmic symptoms and signs may be the first indication of mitochondrial disease and should prompt systemic investigations for potentially life-threatening associations, such as cardiac conduction defects. Finally, the ophthalmologist can offer symptomatic treatments for some of the most disabling manifestations of these disorders.

First submicroscopic inversion of the OPA1 gene identified in dominant optic atrophy - a case report

Background

Dominant optic atrophy (DOA) is an inherited optic neuropathy that mainly affects visual acuity, central visual fields and color vision due to a progressive loss of retinal ganglion cells and their axons that form the optic nerve. Approximately 45–90% of affected individuals with DOA harbor pathogenic variants in the OPA1 gene. The mutation spectrum of OPA1 comprises nonsense, canonical and non-canonical splice site, frameshift and missense as well as copy number variants, but intragenic inversions have not been reported so far.

Case presentation

We report a 33-year-old male with characteristic clinical features of DOA. Whole-genome sequencing identified a structural variant of 2.4 kb comprising an inversion of 937 bp at the OPA1 locus. Fine mapping of the breakpoints to single nucleotide level revealed that the structural variation was an inversion flanked by two deletions. As this rearrangement inverts the entire first exon of OPA1, it was classified as likely pathogenic.

Conclusions

We report the first DOA case harboring an inversion in the OPA1 gene. Our study demonstrates that copy-neutral genomic rearrangements have to be considered as a possible cause of disease in DOA cases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12881-020-01166-z.

Subjective and polysomnographic evaluation of sleep in mitochondrial optic neuropathies

Leber hereditary optic neuropathy and Dominant optic atrophy are associated with a selective loss of retinal ganglion cells (RGC). A subtype of RGC is responsible for light-dependent physiological processes. The aim of our study was to evaluate both subjective and objective sleep parameters in 36 (18 males; mean age 33.8 ± 16.7) symptomatic/asymptomatic subjects with Leber hereditary optic neuropathy and dominant optic atrophy. The Pittsburgh Sleep Quality Index (PSQI), the Epworth Sleepiness Scale (ESS) and nocturnal polysomnography were used to assess sleep disturbances and sleep quality. The questionnaires indicated significantly worse sleep quality (PSQI > 5; average 7.7 ± 3.8) in 21 (70%) and excessive daytime sleepiness (ESS > 10; average 6.3 ± 5.8) in six (20%) individuals. Nocturnal polysomnography has not revealed any significant changes of sleep structure. Rapid eye movement (REM) sleep without atonia was observed in two patients with Leber hereditary optic neuropathy. Obstructive sleep apnea was noted in eight cases. No correlation between subjective and polysomnographic data and no differences between symptomatic and asymptomatic groups were observed. None of the subjects fulfilled criteria for a circadian sleep disorder. In both symptomatic and asymptomatic individuals, a subjective decrease of the quality of sleep and wakefulness was noted without any correlation on polysomnography.

OPA1: 516 unique variants and 831 patients registered in an updated centralized Variome database

BACKGROUND

The dysfunction of OPA1, a dynamin GTPase involved in mitochondrial fusion, is responsible for a large spectrum of neurological disorders, each of which includes optic neuropathy. The database dedicated to OPA1 ( https://www.lovd.nl/OPA1 ), created in 2005, has now evolved towards a centralized and more reliable database using the Global Variome shared Leiden Open-source Variation Database (LOVD) installation.

RESULTS

The updated OPA1 database, which registers all the patients from our center as well as those reported in the literature, now covers a total of 831 patients: 697 with isolated dominant optic atrophy (DOA), 47 with DOA "plus", and 83 with asymptomatic or unclassified DOA. It comprises 516 unique OPA1 variants, of which more than 80% (414) are considered pathogenic. Full clinical data for 118 patients are documented using the Human Phenotype Ontology, a standard vocabulary for referencing phenotypic abnormalities. Contributors may now make online submissions of phenotypes related to OPA1 mutations, giving clinical and molecular descriptions together with detailed ophthalmological and neurological data, according to an international thesaurus.

CONCLUSIONS

The evolution of the OPA1 database towards the LOVD, using unified nomenclature, should ensure its interoperability with other databases and prove useful for molecular diagnoses based on gene-panel sequencing, large-scale mutation statistics, and genotype-phenotype correlations.

Optical Coherence Tomography of the Retinal Ganglion Cell Complex in Leber's Hereditary Optic Neuropathy and Dominant Optic Atrophy

Background: Mitochondrial optic neuropathies such as Leber's Hereditary Optic Neuropathy (LHON) and Dominant Optic Atrophy (DOA) have been shown to produce an optic neuropathy secondary to retinal ganglion cell loss with thinning of the retinal ganglion cell complex (RGCC). Methods: We performed a retrospective analysis assessing the thicknesses of the peripapillary retinal nerve fiber layer (pRNFL) along with the macular retinal ganglion cell-inner plexiform layer (RGC-IPL) using optical coherence tomography (OCT). We compared these changes among acute and chronic LHON, DOA, and normal healthy control patients. Results: Patients with chronic LHON exhibited statistically significant thinning of the RNFL in the superior, nasal, and inferior quadrants of the retina. In acute LHON, the RNFL was relatively thicker in all but the temporal quadrant when compared with respective quadrants in normal eyes; however, statistical significance was not achieved. In DOA, the RNFL was thinnest in the superior and inferior quadrants of the retina, measuring between acute and chronic LHON thickness values. In chronic LHON and DOA, both the pRNFL and RGC-IPL were significantly thinner in all four retinal quadrants relative to controls. Conclusions: This article represents the first comparative study of the RGCC between LHON and DOA. Our findings demonstrated significant thickness reductions in pRNFL and macular RGC-IPL in patients with LHON and DOA, with different specific patterns consistent with the general patterns of thinning classically observed. This study suggests the usefulness of the RGCC as a potential in vivo biomarker for assessing disease in patients with LHON and DOA.

OPA1: How much do we know to approach therapy?

OPA1 is a GTPase that controls several functions, such as mitochondrial dynamics and energetics, mtDNA maintenance and cristae integrity. In the last years, there have been described other cellular pathways and mechanisms involving OPA1 directly or through its interaction. All this new information, by implementing our knowledge on OPA1 is instrumental to elucidating the pathogenic mechanisms of OPA1 mutations. Indeed, these are associated with dominant optic atrophy (DOA), one of the most common inherited optic neuropathies, and with an increasing number of heterogeneous neurodegenerative disorders. In this review, we overview all recent findings on OPA1 protein functions, on its dysfunction and related clinical phenotypes, focusing on the current therapeutic options and future perspectives to treat DOA and the other associated neurological disorders due to OPA1 mutations.

Incomplete penetrance in mitochondrial optic neuropathies

Incomplete penetrance characterizes the two most frequent inherited optic neuropathies, Leber's Hereditary Optic Neuropathy (LHON) and dominant optic atrophy (DOA), due to genetic errors in the mitochondrial DNA (mtDNA) and the nuclear DNA (nDNA), respectively. For LHON, compelling evidence has accumulated on the complex interplay of mtDNA haplogroups and environmental interacting factors, whereas the nDNA remains essentially non informative. However, a compensatory mechanism of activated mitochondrial biogenesis and increased mtDNA copy number, possibly driven by a permissive nDNA background, is documented in LHON; when successful it maintains unaffected the mutation carriers, but in some individuals it might be hampered by tobacco smoking or other environmental factors, resulting in disease onset. In females, mitochondrial biogenesis is promoted and maintained within the compensatory range by estrogens, partially explaining the gender bias in LHON. Concerning DOA, none of the above mechanisms has been fully explored, thus mtDNA haplogroups, environmental factors such as tobacco and alcohol, and further nDNA variants may all participate as protective factors or, on the contrary, favor disease expression and severity. Next generation sequencing, complemented by transcriptomics and proteomics, may provide some answers in the next future, even if the multifactorial model that seems to apply to incomplete penetrance in mitochondrial optic neuropathies remains problematic, and careful stratification of patients will play a key role for data interpretation. The deep understanding of which factors impinge on incomplete penetrance may shed light on the pathogenic mechanisms leading to optic nerve atrophy, on their possible compensation and, thus, on development of therapeutic strategies.

Melanopsin-expressing retinal ganglion cells are resistant to cell injury, but not always

Melanopsin retinal ganglion cells (mRGCs) are intrinsically photosensitive RGCs deputed to non-image forming functions of the eye such as synchronization of circadian rhythms to light-dark cycle. These cells are characterized by unique electrophysiological, anatomical and biochemical properties and are usually more resistant than conventional RGCs to different insults, such as axotomy and different paradigms of stress. We also demonstrated that these cells are relatively spared compared to conventional RGCs in mitochondrial optic neuropathies (Leber's hereditary optic neuropathy and Dominant Optic Atrophy). However, these cells are affected in other neurodegenerative conditions, such as glaucoma and Alzheimer's disease. We here review the current evidences that may underlie this dichotomy. We also present our unpublished data on cell experiments demonstrating that melanopsin itself does not explain the robustness of these cells and some preliminary data on immunohistochemical assessment of mitochondria in mRGCs.

A neurodegenerative perspective on mitochondrial optic neuropathies

Mitochondrial optic neuropathies constitute an important cause of chronic visual morbidity and registrable blindness in both the paediatric and adult population. It is a genetically heterogeneous group of disorders caused by both mitochondrial DNA (mtDNA) mutations and a growing list of nuclear genetic defects that invariably affect a critical component of the mitochondrial machinery. The two classical paradigms are Leber hereditary optic neuropathy (LHON), which is a primary mtDNA disorder, and autosomal dominant optic atrophy (DOA) secondary to pathogenic mutations within the nuclear gene OPA1 that encodes for a mitochondrial inner membrane protein. The defining neuropathological feature is the preferential loss of retinal ganglion cells (RGCs) within the inner retina but, rather strikingly, the smaller calibre RGCs that constitute the papillomacular bundle are particularly vulnerable, whereas melanopsin-containing RGCs are relatively spared. Although the majority of patients with LHON and DOA will present with isolated optic nerve involvement, some individuals will also develop additional neurological complications pointing towards a greater vulnerability of the central nervous system (CNS) in susceptible mutation carriers. These so-called “plus” phenotypes are mechanistically important as they put the loss of RGCs within the broader perspective of neuronal loss and mitochondrial dysfunction, highlighting common pathways that could be modulated to halt progressive neurodegeneration in other related CNS disorders. The management of patients with mitochondrial optic neuropathies still remains largely supportive, but the development of effective disease-modifying treatments is now within tantalising reach helped by major advances in drug discovery and delivery, and targeted genetic manipulation.

Clinical variability in hereditary optic neuropathies: Two novel mutations in two patients with dominant optic atrophy and Wolfram syndrome

Dominant optic atrophy (DOA) and Wolfram syndrome share a great deal of clinical variability, including an association with hearing loss and the presence of optic atrophy at similar ages. The objective of this paper was to discuss the phenotypic variability of these syndromes with respect to the presentation of two clinical cases.

We present two patients, each with either DOA or Wolfram syndrome, and contribute to the research literature through our findings of two novel mutations.

The overlapping of several clinical characteristics in hereditary optic neuropathies can complicate the differential diagnosis. Future studies are needed to better determine the genotype-phenotype correlation for these diseases.

Neuroradiological findings expand the phenotype of OPA1-related mitochondrial dysfunction

OBJECTIVE

OPA1 mutations are responsible for more than half of autosomal dominant optic atrophy (ADOA), a blinding disease affecting the retinal ganglion neurons. In most patients the clinical presentation is restricted to the optic nerve degeneration, albeit in 20% of them, additional neuro-sensorial symptoms might be associated to the loss of vision, as frequently encountered in mitochondrial diseases. This study describes clinical and neuroradiological features of OPA1 patients.

METHODS

Twenty two patients from 17 families with decreased visual acuity related to optic atrophy and carrying an OPA1 mutation were enrolled. Patients underwent neuro-ophthalmological examinations. Brain magnetic resonance imaging (T1, T2 and flair sequences) was performed on a 1.5-Tesla MR Unit. Twenty patients underwent 2-D proton spectroscopic imaging.

RESULTS

Brain imaging disclosed abnormalities in 12 patients. Cerebellar atrophy mainly involving the vermis was observed in almost a quarter of the patients; other abnormalities included unspecific white matter hypersignal, hemispheric cortical atrophy, and lactate peak. Neurological examination disclosed one patient with a transient right hand motor deficit and ENT examination revealed hearing impairment in 6 patients. Patients with abnormal MRI were characterized by: (i) an older age (ii) more severe visual impairment with chronic visual acuity deterioration, and (iii) more frequent associated deafness.

CONCLUSIONS

Our results demonstrate that brain imaging abnormalities are common in OPA1 patients, even in those with normal neurological examination. Lactate peak, cerebellar and cortical atrophies are consistent with the mitochondrial dysfunction related to OPA1 mutations and might result from widespread neuronal degeneration.

[Hereditary optic neuropathies: from clinical signs to diagnosis]

Inherited optic atrophy must be considered when working up any optic nerve involvement and any systemic disease with signs of optic atrophy, even with a negative family history. There are two classical forms: dominant optic atrophy, characterized by insidious, bilateral, slowly progressive visual loss and temporal disc pallor, and Leber's optic atrophy, characterized by acute loss of central vision followed by the same event in the fellow eye within a few weeks to months, with disc hyperemia in the acute phase. Family history is critical for diagnosis. In the absence of family history, the clinician must rule out an identifiable acquired cause, i.e. toxic, inflammatory, perinatal injury, traumatic or tumoral, with orbital and brain imaging (MRI). Recessive optic atrophies are more rare and more severe and occur as part of multisystemic disorders, particularly Wolfram syndrome (diabetes mellitus, diabetes insipidus, and hearing loss). Effective treatments are limited; alcohol and smoking should be avoided. A cyclosporine trial (taken immediately upon visual loss in the first eye) is in progress in Leber's optic atrophy to prevent involvement of the fellow eye.