Mitochondrial optic neuropathies (MON)

The 2025 Jacobson Lecture revealed a scientific journey that began with the Cuban epidemic of blindness to recent studies of the quantum mechanical underpinnings of Leber's Hereditary Optic Neuropathy (LHON). A sudden outbreak of bilaterally symmetrical optic neuropathy and peripheral neuropathy in more than 50,000 Cubans in 1993 had been blamed on a viral infection. Further investigations by our team revealed synergistic toxicity of folic acid deficiency and the consumption of homemade rum containing small amounts of methanol. This research led to subsequent findings relevant to LHON, a maternally inherited mitochondrial disease involving Complex I, resulting in retinal ganglion cell death. Later studies show that this was not due to the depletion of adenosine triphosphate but through the accumulation of reactive oxygen species (ROS). The quantum mechanical model, which identifies alterations of quantum electron tunneling as the origin of spilled ROS, changes our understanding of mitochondrial optic neuropathies and redefines LHON as a disease of oxidative stress rather than energy deficit.

Leber's hereditary optic neuropathy (LHON) is the most common maternally inherited disease linked to mitochondrial DNA (mtDNA). The patients present with subacute asymmetric bilateral vision loss. Approximately 95% of the LHON cases are caused by m.3460G>A (MTND1), m.11778G>A (MTND4), and m.14484T>C (MTND6) mutations. The hallmark of hereditary optic neuropathies determined by mitochondrial dysfunction is the vulnerability and degeneration of retinal ganglion cells (RGC). We present the case of a 28-year-old man who came to our clinic complaining of a subacute decrease in visual acuity of his left eye. From his medical history, we found out that one month before he had the same symptoms in the right eye. From the family history, we noted that an uncle has had vision problems since childhood. We carried out complete blood tests, including specific antibodies for autoimmune and infectious diseases. Laboratory tests and MRI were within normal limits. A blood test of the mtDNA showed the presence of 11778 G>A mutation on the mtND6 gene. The medical history, the fundus appearance, the OCT, and the paraclinical investigations, made us diagnose our patient with Leber's hereditary optic neuropathy. As soon as possible, we began the treatment with systemic idebenone, 900 mg/day. We examined the patient 2, 6, and 10 weeks after initiating the treatment. Abbreviations: LHON = Leber's Hereditary Optic Neuropathy, mtDNA = mitochondrial DNA, VA = visual acuity, RE = right eye, LE = left eye, OCT = Optical coherence tomography, pRNFL = peripapillary retinal nerve fiber layer, GCL = retinal ganglion cells layer, MRI = magnetic resonance imaging, VEP = visual evoked potentials, VEP IT = VEP implicit time, VEP A = VEP amplitude.

Leber's hereditary optic neuropathy (LHON) is a mitochondrial genetic disease in which optic neuropathy is considered a key feature. Several other manifestations of LHON have been reported; however, only little is known of their incidence and the life expectancy in LHON patients. This study, based on Danish nationwide health registries, included 141 patients diagnosed with LHON and 297 unaffected family members in the maternal line. The incidence of comorbidities and mortality for patients with LHON and unaffected family members was compared with that in the general population. Having LHON was associated with an almost 2-fold risk of mortality with a rate ratio (RR) of 1.95 (95% confidence interval [CI]: 1.47-2.59; P < 0.001). The incidence of several diseases was increased for LHON patients, but not for family members. The incidence of stroke was 5.73 per 1000 patient-years for LHON patients compared to 2.33 for the general population, and the RR was 2.38 (95% CI: 1.58-3.58; P < 0.001). The incidence of demyelinating disorders was 2.24 compared to 0.21 for the general population; RR was 12.89 (95% CI: 6.70-24.77; P < 0.001). A 4-fold risk of dementia was seen for LHON patients (RR: 4.26, 95% CI: 1.91-9.48; P < 0.001), incidence 1.45 for LHON and 0.37 for the general population. Moreover, LHON patients had an increased risk of epilepsy, atherosclerosis, nerve symptoms, neuropathy, and alcohol-related disorders. The manifestation of LHON was associated with increased mortality and increased incidence of several disorders including stroke, demyelinating disorder, dementia, and epilepsy.

The pathological mechanisms and novel therapeutics for Leber's hereditary optic neuropathy.

Leber's hereditary optic neuropathy is a maternally inherited disease associated with the late onset of bilateral loss of central vision and cardiac dysrhythmias. The maternal inheritance is explained by the mitochondrial origin of the disease. Analysis of the sequence of a mitochondrial DNA has indicated that a single nucleotide change at position 11778 is associated with this disease. This mutation converts the 340th amino acid of NADH dehydrogenase subunit 4 from an arginine to a histidine and eliminates an SfaNI endonuclease restriction site. A survey of restriction-fragment-length polymorphisms in the mitochondrial DNA of three independent families with this disease (an American black and two white European families) and 10 controls confirmed that this SfaNI site is associated with the disease. A phylogenetic tree for mitochondrial DNA polymorphism and sequence variants from three probands with Leber's disease and four controls was constructed, and the mutation at position 11778 was found to be associated with two mitochondrial DNA backgrounds--an American black mitochondrial DNA and a European mitochondrial DNA. Thus, this mutation must have arisen twice independently. Since the mutation correlated with symptoms of Leber's disease in both cases, these findings indicate that the mutation is a cause of the disease. This genetic analysis has identified the specific point mutation in the mitochondrial DNA that results in Leber's hereditary optic neuropathy.

Optic neuropathies are characterized by the degeneration of the optic nerves and represent a considerable individual and societal burden. Notably, Leber's hereditary optic neuropathy (LHON) is a devastating vision disease caused by mitochondrial gene mutations that hinder oxidative phosphorylation and increase oxidative stress, leading to the loss of retinal ganglion neurons and axons. Loss of vision is rapid and severe, predominantly in young adults. Penetrance is incomplete, and the time of onset is unpredictable. Recent findings revealed that the incidence of genetic LHON susceptibility is around 1 in 1000, much higher than believed till now. Environmental factors are critical in LHON triggering or severity. Families at risk have a very strong demand for how to prevent the onset or limit the severity of the disease. Here, we review recent knowledge of the extrinsic determinants of LHON expression, including lifestyle, dietary supplements, common chemicals, and drugs.

The mechanisms of the complex pathophysiology of Leber's hereditary optic neuropathy (LHON) are still insufficiently clarified. The role of oxidative stress as an etiological factor has been proposed and demonstrated in vitro, but without conclusive data that rely on clinical samples. The aim of the study was to evaluate and characterize the existence of oxidative stress in the plasma of LHON patients and healthy individuals. Whole mitochondrial genome sequencing has been performed in order to identify primary LHON mutations. For the assessment of oxidative stress, the following biomarkers were determined in plasma: total oxidant status (TOS), total antioxidant status (TAS), and oxidative stress index (OSI), while oxidative damage of cellular proteins was estimated by quantifying advanced oxidation protein products (AOPP). All three primary LHON mutations (m.3460G > A, m.11778G > A and m.14484 T > C) were identified as a genetic cause of the disease, where the most prevalent one was m.11778G > A. LHON patients have a highly significant increase of TOS and a marked decrease of TAS levels, which suggests the existence of substantial oxidative stress. OSI is high in LHON patients, which definitely implies the presence of redox imbalance. Elevated level of AOPP in LHON patients refers to the significant deleterious effects of oxidative stress on cellular proteins. Oxidative stress parameters do not significantly differ between LHON individuals with different primary mutations. Both symptomatic and asymptomatic LHON patients have an augmented level of oxidative stress which suggests that primary mutations exhibit a pro-oxidative phenotype. Gender and smoking habit significantly influence examined biochemical parameters when LHON patients are compared with the control group. Different mitochondrial haplogroups are characterized by altered levels of OSI in LHON group. The absence of physiological correlations between redox parameters reflects the deregulation of homeostatic oxidative/antioxidative balance in LHON patients. This is the greatest series of LHON patients that were evaluated for oxidative stress and the first case-controlled study that evaluated TOS, TAS, OSI, and AOPP and their influence on disease phenotype. It is evident that the presence of oxidative stress represents an important pathophysiological event in LHON and that it could potentially serve as a circulatory biomarker for a therapy efficacy understanding.

Chapter 3 - Mitochondrial optic neuropathies

Incomplete penetrance in mitochondrial optic neuropathies

Gene therapy offers a promising treatment for Leber's hereditary optic neuropathy (LHON), a disease of retinal ganglion cell (RGC) degeneration with severe vision loss caused by mitochondria-NADH dehydrogenase 4 (MT-ND4) mutations. However, optimizing mitochondria-targeted gene delivery to promote RGC regeneration and visual-photoreception recovery remains challenging in LHON. Here, mitochondria-targeted wireless charging gold nanoparticles (WCGs), doubling as a wireless charging-mediated gene-delivery platform and electric stimulus-restored phototransduction, are developed for LHON treatment. Upon high-frequency magnetic field (HFMF) irradiation, WCGs enhanced MT-ND4 transfection efficiency, restored complex I activity and mitochondrial homeostasis in vitro, and further promoted RGC neurite outgrowth in LHON patient-derived iPSC-differentiated retinal organoids. Wireless charging combined with electric stimulation also facilitated in vivo gene delivery, effectively promoting neuronal recovery, preventing RGC degeneration, suppressing inflammation, and enhancing retinal electrophysiological function in the damaged retinas of LHON mice. Furthermore, single-cell RNA sequencing and spatiotemporal transcriptomic analysis revealed that HFMF-treatment reprograms Müller glia to enhance dendritic development, restore mitochondrial function, and express phototransduction genes to support photoreceptor function in vivo. Finally, functional retinal-optic-electrophysiological findings with spatiotemporal transcriptomic analysis at the single-cell level support that HFMF synergized with WCG/hND4 therapy, promoting retinal repairment with RGC neurite regeneration and recovering visual phototransduction in LHON mouse models.

Natural History of Leber's Hereditary Optic Neuropathy: Longitudinal Analysis of the Retinal Nerve Fiber Layer by Optical Coherence Tomography

Aim: The aim was to report the phenotypic expression of chronic Leber's hereditary optic neuropathy (LHON) patients with primary and secondary mitochondrial mutations presenting at a tertiary eye care center in South India. Materials and Methods: Of 51 patients suspected to have LHON, 15 patients turned out to be positive for mitochondrial mutations. All 15 patients with LHON are in the chronic phase of the disease and have undergone clinical examination that included visual acuity, fundus examination, visual fields, and optical coherence tomography. Clinical data were compared among the LHON patients with primary mutations of G11778A and T14484C and grouped secondary mutations. Descriptive analysis was reported. Results: There was no significant difference found in visual acuities in both the eyes of the three genotypic groups (G11778A, T14484C, and secondary mutations) (P &gt; 0.05). Retinal nerve fiber layer (RNFL) analysis showed that nine patients carrying G11778A and three patients carrying secondary mutations were similar, while two patients with T14484C showed severe thinning of RNFL in all four quadrants. Conclusions: Among a small percentage of patients who were positive for LHON mutations, severe RNFL thinning was the most prominent finding in the T14484C mutation that differentiates from G11778A and secondary mutations. Other clinical features seem to be similar among all genotypic groups examined.

The m.11778 A > G variant associated with the coexistence of Leber's hereditary optic neuropathy and multiple sclerosis-like illness dysregulates the metabolic interplay between mitochondrial oxidative phosphorylation and glycolysis

This article presents the results of a noncontrolled clinical study of 20 persons with Leber's hereditary optic neuropathy who were treated from 1976 to 1990 at the Low Vision Centre, Finnish Federation of the Visually Handicapped. It emphasizes the importance of early functional visual rehabilitation and the use of low vision aids to help patients perform their daily activities.

Gene Therapy for Leber's Hereditary Optic Neuropathy: Time to Include a True Placebo Arm?