Compartmental Differences in the Retinal Ganglion Cell Mitochondrial Proteome.

Among neurons, retinal ganglion cells (RGCs) are uniquely sensitive to mitochondrial dysfunction. The RGC is highly polarized, with a somatodendritic compartment in the inner retina and an axonal compartment projecting to targets in the brain. The drastically dissimilar functions of these compartments implies that mitochondria face different bioenergetic and other physiological demands. We hypothesized that compartmental differences in mitochondrial biology would be reflected by disparities in mitochondrial protein composition. Here, we describe a protocol to isolate intact mitochondria separately from mouse RGC somatodendritic and axonal compartments by immunoprecipitating labeled mitochondria from RGC MitoTag mice. Using mass spectrometry, 471 and 357 proteins were identified in RGC somatodendritic and axonal mitochondrial immunoprecipitates, respectively. We identified 10 mitochondrial proteins exclusively in the somatodendritic compartment and 19 enriched ≥2-fold there, while 3 proteins were exclusively identified and 18 enriched in the axonal compartment. Our observation of compartment-specific enrichment of mitochondrial proteins was validated through immunofluorescence analysis of the localization and relative abundance of superoxide dismutase ( SOD2 ), sideroflexin-3 ( SFXN3 ) and trifunctional enzyme subunit alpha ( HADHA ) in retina and optic nerve specimens. The identified compartmental differences in RGC mitochondrial composition may provide promising leads for uncovering physiologically relevant pathways amenable to therapeutic intervention for optic neuropathies.

The recurrent deep intronic pseudoexon-inducing variant COL6A1 c.930+189C>T results in a consistently severe phenotype of COL6-related dystrophy: Towards clinical trial readiness for splice-modulating therapy.

Collagen VI-related dystrophies (COL6-RDs) manifest with a spectrum of clinical phenotypes, ranging from Ullrich congenital muscular dystrophy (UCMD), presenting with prominent congenital symptoms and characterised by progressive muscle weakness, joint contractures and respiratory insufficiency, to Bethlem muscular dystrophy, with milder symptoms typically recognised later and at times resembling a limb girdle muscular dystrophy, and intermediate phenotypes falling between UCMD and Bethlem muscular dystrophy. Despite clinical and immunohistochemical features highly suggestive of COL6-RD, some patients had remained without an identified causative variant in COL6A1, COL6A2 or COL6A3. With combined muscle RNA-sequencing and whole-genome sequencing we uncovered a recurrent, de novo deep intronic variant in intron 11 of COL6A1 (c.930+189C>T) that leads to a dominantly acting in-frame pseudoexon insertion. We subsequently identified and have characterised an international cohort of forty-four patients with this COL6A1 intron 11 causative variant, one of the most common recurrent causative variants in the collagen VI genes. Patients manifest a consistently severe phenotype characterised by a paucity of early symptoms followed by an accelerated progression to a severe form of UCMD, except for one patient with somatic mosaicism for this COL6A1 intron 11 variant who manifests a milder phenotype consistent with Bethlem muscular dystrophy. Characterisation of this individual provides a robust validation for the development of our pseudoexon skipping therapy. We have previously shown that splice-modulating antisense oligomers applied in vitro effectively decreased the abundance of the mutant pseudoexon-containing COL6A1 transcripts to levels comparable to the in vivo scenario of the somatic mosaicism shown here, indicating that this therapeutic approach carries significant translational promise for ameliorating the severe form of UCMD caused by this common recurrent COL6A1 causative variant to a Bethlem muscular dystrophy phenotype.

A multi-centre case series of patients with coexistent intracranial hypertension and malignant arterial hypertension.

OBJECTIVE: To describe the clinical characteristics, outcomes, and management of a large cohort of patients with concomitant malignant arterial hypertension and intracranial hypertension. METHODS: Design: Retrospective case series. SUBJECTS: Patients aged ≥ 18 years with bilateral optic disc oedema (ODE), malignant arterial hypertension and intracranial hypertension at five academic institutions. Patient demographics, clinical characteristics, diagnostic studies, and management were collected. RESULTS: Nineteen patients (58% female, 63% Black) were included. Median age was 35 years; body mass index (BMI) was 30 kg/m2. Fourteen (74%) patients had pre-existing hypertension. The most common presenting symptom was blurred vision (89%). Median blood pressure (BP) was 220 mmHg systolic (IQR 199-231.5 mmHg) and 130 mmHg diastolic (IQR 116-136 mmHg) mmHg), and median lumbar puncture opening pressure was 36.5 cmH2O. All patients received treatment for arterial hypertension. Seventeen (89%) patients received medical treatment for raised intracranial pressure, while six (30%) patients underwent a surgical intervention. There was significant improvement in ODE, peripapillary retinal nerve fibre layer thickness, and visual field in the worst eye (p < 0.05). Considering the worst eye, 9 (47%) presented with acuity ≥ 20/25, while 5 (26%) presented with ≤ 20/200. Overall, 7 patients maintained ≥ 20/25 acuity or better, 6 demonstrated improvement, and 5 demonstrated worsening. CONCLUSIONS: Papilloedema and malignant arterial hypertension can occur simultaneously with potentially greater risk for severe visual loss. Clinicians should consider a workup for papilloedema among patients with significantly elevated blood pressure and bilateral optic disc oedema.

Ophthalmic manifestations of MEPAN syndrome.

BACKGROUND: Mitochondrial enoyl CoA reductase protein-associated neurodegeneration (MEPAN) syndrome is an ultra-rare autosomal recessive disorder caused by loss-of-function mutations in the MECR gene. The syndrome is characterized by dystonia in early childhood, basal ganglia signal abnormalities on MRI, and subsequent optic atrophy, with relative sparing of cognition. We characterize the ophthalmic manifestations observed in a patient with MEPAN syndrome, as a detailed account of ocular findings has not been published to date. METHODS: Case study of a patient with genetically confirmed MEPAN syndrome, with full ophthalmic evaluation including slit-lamp exam, sensorimotor exam, fundus photography, retinal ocular coherence tomography (OCT), electroretinography, visual evoked potentials, and visual field testing. RESULTS: The patient exhibited decreased visual acuity of 20/150 in both eyes with moderate dyschromatopsia on pseudoisochromatic plate testing, while peripheral vision was largely intact on Goldmann visual field testing. Fundus exam revealed bilateral optic atrophy with pallor most pronounced temporally, corresponding to OCT findings of diffuse retinal nerve fiber layer thinning most prominent in the papillomacular bundle region and severe ganglion cell layer thinning in the maculae. She also displayed a high frequency horizontal end-gaze nystagmus and symmetric bilateral external ophthalmoplegia. CONCLUSIONS: The pattern of bilateral optic atrophy in our patient with MEPAN syndrome shows predilection for the papillomacular bundle, similar to that seen in other mitochondrial disorders with optic neuropathy, such as Leber Hereditary Optic Neuropathy and Dominant Optic Atrophy. Our patient's external ophthalmoplegia is another neuro-ophthalmic finding that may be seen in patients with heritable mitochondrial disease, either as an isolated ocular phenotype or within a constellation of systemic manifestations.

Continuous Hypoxia Reduces Retinal Ganglion Cell Degeneration in a Mouse Model of Mitochondrial Optic Neuropathy.

Purpose: To test whether continuous hypoxia is neuroprotective to retinal ganglion cells (RGCs) in a mouse model of mitochondrial optic neuropathy. Methods: RGC degeneration was assessed in genetically modified mice in which the floxed gene for the complex I subunit NDUFS4 is deleted from RGCs using Vlgut2-driven Cre recombinase. Beginning at postnatal day 25 (P25), Vglut2-Cre;ndufs4loxP/loxP mice and control littermates were housed under hypoxia (11% oxygen) or kept under normoxia (21% oxygen). Survival of RGC somas and axons was assessed at P60 and P90 via histological analysis of retinal flatmounts and optic nerve cross-sections, respectively. Retinal tissue was also assessed for gliosis and neuroinflammation using western blot and immunofluorescence. Results: Consistent with our previous characterization of this model, at least one-third of RGCs had degenerated by P60 in Vglut2-Cre;ndufs4loxP/loxP mice remaining under normoxia. However, continuous hypoxia resulted in complete rescue of RGC somas and axons at this time point, with normal axonal myelination observed on electron microscopy. Though only partial, hypoxia-mediated rescue of complex I-deficient RGC somas and axons remained significant at P90. Hypoxia prevented reactive gliosis at P60, but the retinal accumulation of Iba1+ mononuclear phagocytic cells was not substantially reduced. Conclusions: Continuous hypoxia achieved dramatic rescue of early RGC degeneration in mice with severe mitochondrial dysfunction. Although complete rescue was not durable to P90, our observations suggest that investigating the mechanisms underlying hypoxia-mediated neuroprotection of RGCs may identify useful therapeutic strategies for optic neuropathies resulting from less profound mitochondrial impairment, such as Leber hereditary optic neuropathy.

Association Between Lysine Reduction Therapies and Cognitive Outcomes in Patients With Pyridoxine-Dependent Epilepsy.

BACKGROUND AND OBJECTIVES: Pyridoxine-dependent epilepsy (PDE-ALDH7A1) is a developmental epileptic encephalopathy characterized by seizure improvement after pyridoxine supplementation. Adjunct lysine reduction therapies reduce the accumulation of putative neurotoxic metabolites with the goal to improve developmental outcomes. Our objective was to examine the association between treatment with lysine reduction therapies and cognitive outcomes. METHODS: Participants were recruited from within the International Registry for Patients with Pyridoxine-Dependent Epilepsy from August 2014 through March 2021. The primary outcome was standardized developmental test scores associated with overall cognitive ability. The relationship between test scores and treatment was analyzed with multivariable linear regression using a mixed-effects model. A priori, we hypothesized that treatment in early infancy with pyridoxine and lysine reduction therapies would result in a normal developmental outcome. A sub-analysis was performed to evaluate the association between cognitive outcome and lysine reduction therapies initiated in the first six months of life. RESULTS: A total of 112 test scores from 60 participants were available. On average, treatment with pyridoxine and lysine reduction therapies was associated with a non-significant increase of 6.9 points (95% CI -2.7 to 16.5) on developmental testing compared to treatment with pyridoxine alone. For the sub-analysis, a total of 14 developmental testing scores were available from 8 participants. On average, treatment with pyridoxine and lysine reduction therapies in the first six months of life was associated with a significant increase of 21.9 points (95% CI 1.7 to 42.0) on developmental testing. DISCUSSION: Pyridoxine and lysine reduction therapies at any age was associated with mild improvement in developmental testing and treatment in early infancy was associated with a clinically significant increase in developmental test scores. These results provide insight into the mechanism of intellectual and developmental disability in PDE-ALDH7A1 and emphasize the importance of treatment in early infancy with both pyridoxine and lysine reduction therapies. CLASSIFICATION OF EVIDENCE: This study provides Class IV evidence that in PDE-ALDH7A1, pyridoxine plus lysine reduction therapies compared to pyridoxine alone is not significantly associated with overall higher developmental testing scores, but treatment in the first six months of life is associated with significantly higher developmental testing scores.

Timing of therapy and neurodevelopmental outcomes in 18 families with pyridoxine-dependent epilepsy.

BACKGROUND: Seventy-five percent of patients with pyridoxine-dependent epilepsy due to α-aminoadipic semialdehyde dehydrogenase deficiency (PDE-ALDH7A1) suffer intellectual developmental disability despite pyridoxine treatment. Adjunct lysine reduction therapies (LRT), aimed at lowering putative neurotoxic metabolites, are associated with improved cognitive outcomes. However, possibly due to timing of treatment, not all patients have normal intellectual function. METHODS: This retrospective, multi-center cohort study evaluated the effect of timing of pyridoxine monotherapy and pyridoxine with adjunct LRT on neurodevelopmental outcome. Patients with confirmed PDE-ALDH7A1 with at least one sibling with PDE-ALDH7A1 and a difference in age at treatment initiation were eligible and identified via the international PDE registry, resulting in thirty-seven patients of 18 families. Treatment regimen was pyridoxine monotherapy in ten families and pyridoxine with adjunct LRT in the other eight. Primary endpoints were standardized and clinically assessed neurodevelopmental outcomes. Clinical neurodevelopmental status was subjectively assessed over seven domains: overall neurodevelopment, speech/language, cognition, fine and gross motor skills, activities of daily living and behavioral/psychiatric abnormalities. RESULTS: The majority of early treated siblings on pyridoxine monotherapy performed better than their late treated siblings on the clinically assessed domain of fine motor skills. For siblings on pyridoxine and adjunct LRT, the majority of early treated siblings performed better on clinically assessed overall neurodevelopment, cognition, and behavior/psychiatry. Fourteen percent of the total cohort was assessed as normal on all domains. CONCLUSION: Early treatment with pyridoxine and adjunct LRT may be beneficial for neurodevelopmental outcome. When evaluating a more extensive neurodevelopmental assessment, the actual impairment rate may be higher than the 75% reported in literature. TAKE- HOME MESSAGE: Early initiation of lysine reduction therapies adjunct to pyridoxine treatment in patients with PDE-ALDH7A1 may result in an improved neurodevelopmental outcome.

At this junction .

An 81-year-old woman developed painful vision loss to hand motions in the right eye over a several-day period. Dilated fundus examination revealed no acute pathology, but automated perimetry showed a superotemporal visual field defect in the asymptomatic left eye, suggestive of a junctional defect. Magnetic resonance imaging demonstrated enhancement of the right optic nerve extending to its junction with the optic chiasm. The patient's vision failed to improve with intravenous corticosteroids, but demonstrated significant improvement with therapeutic plasma exchange. She was subsequently found to be seropositive for aquaporin-4 autoantibodies, confirming the diagnosis of neuromyelitis optic spectrum disorder.

BILATERAL PARACENTRAL ACUTE MIDDLE MACULOPATHY AFTER CARDIOPULMONARY BYPASS.

PURPOSE: To report the first two observations of bilateral paracentral acute middle maculopathy in the early postoperative period after cardiopulmonary bypass procedures. METHODS: Comprehensive ophthalmic examinations were performed, including best-corrected visual acuity, Humphrey visual field testing, dilated fundus examination, and optical coherence tomography. RESULTS: Two patients complained of unilateral vision loss after cardiac surgery involving cardiopulmonary bypass. Unilateral optic disc edema consistent with ischemic optic neuropathy was observed in the symptomatic eye of each patient, whereas scattered cotton-wool spots were identified bilaterally. In addition, optical coherence tomography imaging revealed bilateral paracentral acute middle maculopathy, correlating with visual field defects detected on automated perimetry in the asymptomatic eyes. CONCLUSION: Although symptomatic postoperative vision loss is a rare complication of cardiac surgery, intraoperative retinal microvascular nonperfusion as a consequence of extracorporeal circulation of blood may be a more common and under-recognized occurrence.

Untargeted metabolomics and infrared ion spectroscopy identify biomarkers for pyridoxine-dependent epilepsy.

BackgroundPyridoxine-dependent epilepsy (PDE-ALDH7A1) is an inborn error of lysine catabolism that presents with refractory epilepsy in newborns. Biallelic ALDH7A1 variants lead to deficiency of α-aminoadipic semialdehyde dehydrogenase/antiquitin, resulting in accumulation of piperideine-6-carboxylate (P6C), and secondary deficiency of the important cofactor pyridoxal-5'-phosphate (PLP, active vitamin B6) through its complexation with P6C. Vitamin B6 supplementation resolves epilepsy in patients, but intellectual disability may still develop. Early diagnosis and treatment, preferably based on newborn screening, could optimize long-term clinical outcome. However, no suitable PDE-ALDH7A1 newborn screening biomarkers are currently available.MethodsWe combined the innovative analytical methods untargeted metabolomics and infrared ion spectroscopy to discover and identify biomarkers in plasma that would allow for PDE-ALDH7A1 diagnosis in newborn screening.ResultsWe identified 2S,6S-/2S,6R-oxopropylpiperidine-2-carboxylic acid (2-OPP) as a PDE-ALDH7A1 biomarker, and confirmed 6-oxopiperidine-2-carboxylic acid (6-oxoPIP) as a biomarker. The suitability of 2-OPP as a potential PDE-ALDH7A1 newborn screening biomarker in dried bloodspots was shown. Additionally, we found that 2-OPP accumulates in brain tissue of patients and Aldh7a1-knockout mice, and induced epilepsy-like behavior in a zebrafish model system.ConclusionThis study has opened the way to newborn screening for PDE-ALDH7A1. We speculate that 2-OPP may contribute to ongoing neurotoxicity, also in treated PDE-ALDH7A1 patients. As 2-OPP formation appears to increase upon ketosis, we emphasize the importance of avoiding catabolism in PDE-ALDH7A1 patients.FundingSociety for Inborn Errors of Metabolism for Netherlands and Belgium (ESN), United for Metabolic Diseases (UMD), Stofwisselkracht, Radboud University, Canadian Institutes of Health Research, Dutch Research Council (NWO), and the European Research Council (ERC).

Traumatic chiasmopathy following mild trauma in a patient with thyroid orbitopathy.

PURPOSE: Traumatic injury to the optic chiasm is rare and most frequently caused by high-velocity head trauma. It classically results in bitemporal hemianopsia and often presents in conjunction with multiple other traumatic injuries, such as skull fractures and cerebrospinal fluid leaks. We present the case of a 40-year-old woman with pre-existing thyroid orbitopathy who struck her forehead after a fall from standing height. OBSERVATIONS: This patient suffered immediate profound unilateral vision loss from traumatic optic neuropathy and possible optic nerve avulsion. The fellow eye manifested a temporal hemianopsia with delayed retinal nerve fiber layer and nasal hemimacular ganglion cell layer thinning on optical coherence tomography, consistent with chiasmal pathology. Magnetic resonance imaging showed no definitive lesions at the optic chiasm or more posteriorly along the afferent visual pathway. CONCLUSIONS AND IMPORTANCE: This patient's severe vision loss suggests that proptosis from thyroid orbitopathy can sensitize the anterior visual pathway to trauma. In this case, we propose that the lack of laxity in the intra-orbital optic nerves allowed transmission of stretching forces to the optic chiasm in the setting of low-velocity blunt trauma.

Magnetic Resonance Imaging Abnormalities of the Optic Nerve Sheath and Intracranial Internal Carotid Artery in Giant Cell Arteritis.

BACKGROUND: Giant cell arteritis (GCA) is an important diagnostic consideration in elderly patients with vision changes. Superficial temporal artery biopsy (TAB) has long been considered the gold standard diagnostic approach for GCA, but MRI has gained interest as an alternative diagnostic modality. Although most of the literature has focused on imaging abnormalities of branches of the external carotid artery, there have been a few reports of GCA-related inflammatory involvement of the orbit and internal carotid arteries (ICAs) on MRI. METHODS: This was a retrospective cross-sectional study of patients undergoing TAB at a single tertiary referral center over a 5-year period. Patients who had undergone contrast-enhanced MRI of the brain and orbits within 1 month of biopsy were included. Fifty-four TAB-positive and 78 TAB-negative patients were reviewed, with the MRI studies of 7 TAB-positive and 6 TAB-negative patients deemed adequate for interpretation. MRI studies were reviewed by 2 masked neuroradiologists, and the findings were correlated with biopsy results and clinical findings. RESULTS: Intracranial ICA vessel wall enhancement was identified in 6 of 7 TAB-positive patients (sensitivity 86%), compared with 2 of 6 TAB-negative patients (specificity 67%). Optic nerve sheath enhancement was identified in 5 of 7 TAB-positive patients (sensitivity 71%) and in 2 of 6 TAB-negative patients (specificity 67%), bilateral in all such cases. The combination of both abnormal imaging findings was observed in 5 of 7 TAB-positive patients (sensitivity 71%) and in none of the 6 TAB-negative patients (specificity 100%). CONCLUSIONS: Intracranial ICA and optic nerve sheath enhancement were observed in a majority of patients with TAB-proven GCA, and the combination of these findings was highly specific for GCA. Identification of these abnormalities on MRI should raise concern for GCA and prompt a thorough review of systems, laboratory testing, and consideration of TAB in patients with ocular complaints potentially consistent with ischemia.

QUANTITATIVE TOPOGRAPHIC CURVATURE MAPS OF THE POSTERIOR EYE UTILIZING OPTICAL COHERENCE TOMOGRAPHY.

PURPOSE: Deformations of the retina such as staphylomas in myopia or scleral flattening in high intracranial pressure can be challenging to quantify with en face imaging. We describe an optical coherence tomography-based method for the generation of quantitative posterior eye topography maps in normal and pathologic eyes. METHODS: Using "whole eye" optical coherence tomography, we corrected for subjects' optical distortions to generate spatially accurate posterior eye optical coherence tomography volumes and created local curvature (KM, mm-1) topography maps for each consented subject. We imaged nine subjects, three normal, two with myopic degeneration, and four with papilledema including one that was imaged longitudinally. RESULTS: Normal subjects mean temporal KM was 0.0923 mm-1, nasal KM was 0.0927 mm-1, and KM local variability was 0.0162 mm-1. In myopic degeneration, subjects KM local variability was higher at 0.0836 mm-1. In papilledema subjects nasal KM was flatter compared with temporal KM (0.0709 vs. 0.0885 mm-1). Mean intrasession KM repeatability for all subjects was 0.0036 mm-1. CONCLUSION: We have developed an optical coherence tomography based method for quantitative posterior eye topography that offers the ability to analyze local curvature with micron scale resolution and offers the potential to help clinicians and researchers characterize subtle, local retinal deformations earlier in patients and follow their development over time.

Neuromyelitis optica spectrum disorder and myelin oligodendrocyte glycoprotein associated disorder-optic neuritis: a comprehensive review of diagnosis and treatment.

Optic neuritis (ON) is the most common cause of acute optic neuropathy in patients younger than 50 years of age and is most frequently idiopathic or associated with multiple sclerosis. However, the discovery of aquaporin-4 immunoglobulin G (IgG) and myelin oligodendrocyte glycoprotein (MOG)-IgG as biomarkers for two separate central nervous system inflammatory demyelinating diseases has revealed that neuromyelitis optica spectrum disorder (NMSOD) and MOG-IgG-associated disease (MOGAD) are responsible for clinically distinct subsets of ON. NMOSD-ON and MOGAD-ON both demonstrate tendencies for bilateral optic nerve involvement and often exhibit a relapsing course with the potential for devastating long-term visual outcomes. Early and accurate diagnosis is therefore essential. This review will summarize the current understanding of the clinical spectra of NMOSD and MOGAD, the radiographic and serological findings which support their diagnoses, and the current evidence behind various acute and long-term therapeutic strategies for ON related to these conditions. A particular emphasis is placed on a number of recent multi-centre randomized placebo-controlled trials, which provide the first level I evidence for long-term treatment of NMOSD.