A Typical Case Presentation with Spontaneous Visual Recovery in Patient Diagnosed with Leber Hereditary Optic Neuropathy Due to Rare Point Mutation in MT-ND4 Gene (m.11253T>C) and Literature Review

Leber hereditary optic neuropathy (LHON) is one of the most common inherited mitochondrial optic neuropathies, caused by mitochondrial DNA (mtDNA) mutations. Three most common mutations, namely m.11778G>A, m.14484T>G and m.3460G>A, account for the majority of LHON cases. These mutations lead to mitochondrial respiratory chain complex I damage. Typically, LHON presents at the 15–35 years of age with male predominance. LHON is associated with severe, subacute, painless bilateral vision loss and account for one of the most common causes of legal blindness in young individuals. Spontaneous visual acuity recovery is rare and has been reported in patients harbouring m.14484T>C mutation. Up to date LHON treatment is limited. Idebenone has been approved by European Medicines Agency (EMA) to treat LHON. However better understanding of disease mechanisms and ongoing treatment trials are promising and brings hope for patients. In this article we report on a patient diagnosed with LHON harbouring rare m.11253T>C mutation in MT-ND4 gene, who experienced spontaneous visual recovery. In addition, we summarise clinical presentation, diagnostic features, and treatment.


Introduction
Leber hereditary optic neuropathy (LHON) is one of the most frequent mitochondrial disorders and hereditary optic neuropathies. It is caused by mitochondrial deoxyribonucleic acid (DNA) mutation. The three most common point mutations result in damage of the mitochondrial respiratory chain complex I. LHON affects young individuals (usually from the age of 15 to 35) with male predominance [1]. Acute, painless bilateral loss of central vision is the main symptom of this disease which makes young people legally blind (V < 0.05) within a few months from disease onset. The loss of vision is usually irreversible, however cases describing spontaneous vision recovery have been reported [2]. In 2014, 120 new cases of LHON were diagnosed in Japan, the population of which is estimated to be approximately 127 million [3]. According to various meta-analysis from Europe, the prevalence of LHON is about 1:45,000, while the incidence of LHON is 1:1,000,000 [2].

Clinical Features
LHON is one of the mitochondrial diseases which in majority of cases exclusively affects eye structures. However, a proportion of cases has been reported to express additional neurological symptoms [14][15][16] or white matter lesions, similar to multiple sclerosis (MS) [17,18]. In such cases, the disease is called LHON plus syndrome.

1.
Functional: • Bilateral, painless subacute failure of central vision. In majority of cases, the second eye is usually affected within the period of 12 months (the average is 3-4 months) since initial presentation. Bilateral concurrent visual loss occurs in about 25 percent of the patients. In most cases visual acuity ranges between counting fingers to perception of light which make patients legally blind (V < 0.05). Spontaneous partial visual regression is possible in rare cases and it is more likely to happen for the patients who have m.14484T>C mutation than for those with m.11778G>A or m.3460G>A pathogenic variant [2]. Other factors of better prognosis were estimated, such as earlier onset of LHON (age < 10 years), subacute manifestation of LHON with slow deterioration of visual acuity and a relatively large optic nerve disc [19][20][21]. • Loss of colour vision affecting mostly the red-green system [20]. • Visual field testing shows dense central or centrocecal scotoma [21,22]. • Reduced contrast sensitivity.

•
Electrophysiological studies: pattern electroretinography (pERG) and visual evoked potentials (VEP) show dysfunction of the optic nerve and the retinal ganglion cells [23]. Some studies show that recording photopic negative response (phNR) could be an informative test in LHON [24].  [25,26]. Some individuals with LHON, usually women, may develop a progressive multiple sclerosis (MS) like illness [27]. The loss of vision is different from the classic LHON: recurrent episodes of visual loss that can be associated with ocular pain occur. After each such episode loss of vision regresses only partially and this eventfully leads to total blindness for half of the patients [27]. Also, with bilateral optic neuropathy, disseminated central nervous system demyelination, characterized by periventricular white matter lesions, develops for these patients but oligoclonal bands in the cerebrospinal fluid are absent [28][29][30].

Stages of LHON
According to consensus, LHON has the following stages:

1.
Asymptomatic (the carriers of the mutation). Using optical coherence tomography (OCT) imaging, thickening of the temporal retinal nerve fibre layer was confirmed in asymptomatic individuals with a LHON-causing mtDNA pathogenic variant, providing evidence that the papillomacular bundle is particularly vulnerable in LHON [31].

2.
Subacute (from the manifestation of LHON to 6 months). Patients are usually asymptomatic until they develop visual blurring affecting the central visual field in the first eye (acute phase). Similar symptoms appear in the other eye an average of two to three months later, so that both eyes are affected in the majority of cases within six months. Unilateral damage of the optic nerve is very rare in patients with LHON and in such cases another underlying pathologic process should be actively excluded. The most common characteristic is an enlarging central or centrocecal scotoma and as the field defect increases in size and density, visual acuity deteriorates to the level of counting fingers or worse. In this stage, even for the asymptomatic patients, specific alterations of the fundus could be observed: retinal telangiectasia of the peripapillary vessels, edema of the peripapillary retinal nerve fibre layer, which progress, and eventually atrophy of optic nerve occurs [5].

3.
Dynamic (from months 6 to 12). Alterations of the fundus, which occur in the subacute stage, are slowly regressing: the edema of the peripapillary retinal nerve fibre layer is decreasing.

4.
Chronic (more than 12 months). In this stage, optic nerve atrophy is progressing at various rates: it could be observed from 6 weeks to more than 1 year after the loss of vision. Central or centrocecal scotoma is enlarging. Most patients remain severely visually impaired and are within the legal requirements for blind registration [32]. OCT shows the retinal fibre layer thinning, especially in temporal zones.

Diagnostics
LHON diagnosis is established when ophthalmological symptoms (or signs) are recognized and/or one of the mitochondrial DNA pathogenic variants are diagnosed by molecular genetic tests. It is important to exclude other possible cause of optic neuropathy ( Figure 1). ** Cardiac conduction defects and LHON: a Finnish study showed an increased incidence of cardiac arrhythmias secondary to accessory pathways in association with LHON [33], but this finding was not noticed when other populations were examined [34]. *** Neuroradiological tests: MRI results are often normal but may reveal white matter lesions and/or a high signal within the optic nerves [35]. Also, MRI could show thinned optic nerves and optic tract.
Genetic testing: Medical history: Su bacu te p ainless bilateral vision loss at a young age.

Symptoms:
• B ilateral su bacu te p ainless vision loss at a young age.
• Fam ily history of blindness in young age. • In m ost cases visual acuity ranges betw een cou nting fin gers to perception of light.
• V isual field testing show s an en larging d ense central or centrocecal scotom a.
• Preserved pupillary ligh t reflex.   a Finnish study showed an increased incidence of cardiac arrhythmias secondary to accessory pathways in association with LHON [33], but this finding was not noticed when other populations were examined [34]. *** Neuroradiological tests: MRI results are often normal but may reveal white matter lesions and/or a high signal within the optic nerves [35]. Also, MRI could show thinned optic nerves and optic tract.

2.
A multi-gene panel that includes the mitochondrial genes namely, MT-ND1, MT-ND2, MT-ND4, MT-ND4L, MT-ND5, and MT-ND6, that encode subunits of NADH dehydrogenase. The included genes and the sensitivity of multi-gene panels vary by laboratory and over time. Performing this test, not only the most frequent but also rare pathological variants could be determined [42].

3.
Whole mtDNA sequencing if pathogenic variant has not been identified during previous genetic testing.

Treatment
Multiple LHON treatment trials were carried out in order to find the best treatment option for LHON. This includes various neuroprotective agents, stem cell therapy, infrared radiation therapy and even gene therapy [43][44][45][46][47][48][49][50] (Table 1). The most promising of these methods are gene and stem cell therapies but further research is needed to evaluate their effectiveness [51,52]. Increase mitochondrial respiration and simultaneously scavenges free radicals to reduce reactive oxygen species (ROS) and toxic acyl coenzyme A molecules [53].
Effective in combination with Idobenem [54] but effectiveness used as monotherapy in patients with Leber hereditary optic neuropathy (LHON) remains limited and variable [53,55].
Failed in a clinical trial for prophylaxis for second eye involvement in LHON carriers [57].

Cyclosporin A
Has an antiapoptotic effect by holding the mitochondrial permeability transition pore closed [58].
It was thought that these drugs may be beneficial in the early stages of LHON by modifying the natural disease progression but study showed that they did not prevent second-eye involvement [59].

Phytoestrogens
Targeting estrogen receptor b improve cell viability by reducing apoptosis, inducing mitochondrial biogenesis and strongly reducing the levels of ROS in LHON cells [60]. Idebenone is the first and the only approved medication for LHON treatment. Idebenone (Raxone) was approved by European Medicines Agency (EMA) in September of 2015. The recommended dose is 900 mg/day (300 mg, 3 times a day). It is an antioxidant which is capable of transferring electrons directly to complex III of the mitochondrial electron transport chain, thereby circumventing complex I (which is damaged due to LHONcausing mtDNA mutations) and restoring cellular energy (ATP-adenosine triphosphate) generation in the cells [43]. In accordance with this biochemical mechanism, Idebenone may re-activate viable but inactive retinal ganglion cells in LHON patients. This was confirmed by in vivo testing [44]. According to international LHON consensus [48], Idebenone treatment not only prevents regression of the visual function but also improves it.

Case Report
At the age of 21 male patient of Lithuanian origin presented with sudden painless central vision loss in both eyes. At that time visual acuity (Snellen chart, Landolt C optotype) was 0.3 in both eyes. At the age of 25 based on increased levels of chloride in the sweat, recurrent respiratory infections caused by pathogens specific for cystic fibrosis (P. Aeruginosa, S. Aureus), insufficient respiratory function and positive tests for fecal elastase, patient was diagnosed with cystic fibrosis (CF). Later, a genetic molecular research using a sequencing denaturing gradient gel electrophoresis (DGGE) fluorescent-polymerase chain reaction method searching for cystic fibrosis transmembrane conductance regulator (CFTR) gene was conducted, which was negative. At the age of 27 chloride levels in the sweat were almost normal, a gene responsible for the CF was not yet found and so a multidiscipline team of specialists made a conclusion that the diagnosis of CF can not be determined. In addition, patient was diagnosed with asthma. At the age 4 patient had episodes manifesting with ataxia, headaches, and changes in the electroencephalography (EEG), hence diagnosis of epilepsy is not established yet. Patient is a non-smoker and denies any past and present alcohol or recreational drug use.
There was no relevant family history. Intraocular pressure (IOP) was normal (right eye-13.3 mmHg; left eye-15 mmHg). On slit lamp examination, the findings of the anterior segment were within normal limits. Ophthalmoscopy revealed bilateral optic nerve atrophy (Figure 2a  Visual field test revealed bilateral central scotomas (Figure 3a,b). Fundus examination showed bilateral optic nerve atrophy (Figure 2a,b). Visual electrophysiology, visual evoked potentials, were performed which showed diminished latency in the right eye, with an prolonged latency in the left eye.   Neurological examination and neuroimaging studies showed slender optic nerves and atrophy of chiasm, without any signs of neuroinflammatory process or compressive lesions ( Figure 5). Neurological examination and neuroimaging studies showed slender optic nerves and atrophy of chiasm, without any signs of neuroinflammatory process or compressive lesions ( Figure 5).  Neurological examination and neuroimaging studies showed slender optic nerves and atrophy of chiasm, without any signs of neuroinflammatory process or compressive lesions ( Figure 5). The usual blood test and inflammatory tests were within normal limit. During follow up visits no new signs or symptoms were noticed. During the latest patient visit (2018) we were able to perform genetic studies, whole mitochondrial DNA sequencing was initiated ( Figure 6 TA, MT-TT, MT-TP, MT-TE, MT-TL2, MT-TS2, MT-TH, MT-TR, MT-TG, MT-TK, MT-TD, MT-TS1, MT-TC, MT-TY, MT-TN, MT-TW,  MT-TM, MT-TI, MT-TQ, MT-TL1, MT-TF, MT-TV. A homoplasmic pathogenic variant NC_012920: m.11253T>C p.(Ile165Thr) in MT-ND4 gene was identified.
Based on the clinical presentation, ophthalmological investigations findings and whole mtDNA sequencing results, the diagnosis of LHON caused by pathogenic variant m.11253T>C in MT-ND4 gene was established.
Visual acuity remained stable until the patient was 25 years old (2018) when a sudden visual recovery was documented (a gain of 3 and 4 lines for the right and left eye, respectively) with no change in structural appearance.
At the age of 26 (5 years since disease onset), 2019 May treatment with Idebenone was initiated with a daily dose of 300 mg 3 times a day. Five months later patient's visual acuity kept improving with 0.8 (right eye) and 0.9 (left eye).  TA, MT-TT, MT-TP, MT-TE, MT-TL2,  MT-TS2, MT-TH, MT-TR, MT-TG, MT-TK, MT-TD, MT-TS1, MT-TC, MT-TY, MT-TN, MT-TW, MT-TM, MT-TI, MT-TQ, MT-TL1, MT-TF, MT-TV. A homoplasmic pathogenic variant NC_012920: m.11253T>C p.(Ile165Thr) in MT-ND4 gene was identified. Visual acuity remained stable until the patient was 25 years old (2018) when a sudden visual recovery was documented (a gain of 3 and 4 lines for the right and left eye, respectively) with no change in structural appearance.
At the age of 26 (5 years since disease onset), 2019 May treatment with Idebenone was initiated with a daily dose of 300 mg 3 times a day. Five months later patient's visual acuity kept improving with 0.8 (right eye) and 0.9 (left eye).

Discussion
We report a case of LHON which was caused by a rare point mutation in MT-ND4 gene. The patient was identified to carry pathogenic m.11253T>C (MT-ND4) variant, which previously has been reported in patient with LHON with spontaneous visual recovery [63].
Spontaneous partial visual recovery is rare and it is mostly observed in patients harbouring m.14484T>C mutation [19,20,64]. It is known that the progression of LHON for patients with this mutation is milder and the chance of visual improvement is from 37 to

Discussion
We report a case of LHON which was caused by a rare point mutation in MT-ND4 gene. The patient was identified to carry pathogenic m.11253T>C (MT-ND4) variant, which previously has been reported in patient with LHON with spontaneous visual recovery [63].
Spontaneous partial visual recovery is rare and it is mostly observed in patients harbouring m.14484T>C mutation [19,20,64]. It is known that the progression of LHON for patients with this mutation is milder and the chance of visual improvement is from 37 to 71%. In comparison, patients with m.11778G>A and m.3460G>A mutations have only a 4% chance of spontaneous recovery [2].
There are some reports of LHON cases which are caused by rare mutations and later spontaneous clinical recovery was noticed. Emperador et al. published a case where LHON was likely to be caused by m.13094T>C and m.15527C>T mutations in a 10-year-old boy who later experienced spontaneous visual recovery [65].
The m.11253T>C mutation which is associated with LHON in our patient, has previously been reported in patient with proven Parkinson's disease [63], hence our patient's family history is negative for this neurodegenerative disorder.
To date, the mechanism of spontaneous visual recovery in LHON remains unknown. Recently it was noted that remission is quite common if LHON manifests in childhood [65] but such cases are rare. Ramos et al. in their study showed that relatively bigger optic nerve head could be a prognostic factor for a spontaneous visual recovery in LHON patients [18]. Moon and others carried out a retrospective study where they tried to identify some factors of possible spontaneous visual recovery which was described as a gain of 3 or more lines. 21 of 80 eyes had visual recovery and such patients were younger at LHON onset (21 vs. 29 years old) and had better vision at the nadir. In the study, fundus photos were evaluated, and it was noticed that the presence of peripapillary telangiectasia and optic disc hyperemia may serve as predictive factors for poor visual prognosis in patients with LHON [66]. In comparison, our patient was 25 years old when the visual recovery happened, and the visual acuity was 0.3 at the nadir. Also, there were not any peripapillary telangiectasias or optic disc hyperemia during ophthalmoscopy and optic nerve head size was medium in both eyes.
Our case also showed that treatment with Idebenone could be effective even after spontaneous remission already occurred and atrophy of optic nerve disc developed. Initially Idebenone was only recommended for patients in early LHON stages but Pemp et al. conducted a research which revealed that this treatment is effective even in late stages when optic nerve atrophy had developed. Treatment was started in seven patients 5 to 51 years after LHON onset and there was a significant increase in visual acuity by an average of −0.20 ± 0.10 logMAR or 10 ± 5 ETDRS letters [67]. This proves that Idebenone should be prescribed even if the LHON is found in the late stages.
Author Contributions: R.L. and B.G. conceived and designed the experiments; R.L. performed the experiments; N.J. and B.G. analyzed the data; R.L., A.S. and L.K. contributed to materials and analysis tools; R.L. and A.S. wrote the paper, R.Z., A.G. and L.A.-B. revised paper. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.

Institutional Review Board Statement:
This study approved by Kaunas Regional Ethics Committee for Biomedical Research, approved code: Nr-BE-2-102, approved date: 6, September 2019.
Informed Consent Statement: Informed consent was obtained from all subjects involved in the study.
Data Availability Statement: All data could be seen in this manuscript.

Conflicts of Interest:
The authors declare no conflict of interest.