Leber hereditary optic neuropathy plus dystonia, and transverse myelitis due to double mutations in MT-ND4 and MT-ND6

Pearls & Oy-sters: Leber Hereditary Optic Neuropathy-Plus Masquerading as Neuromyelitis Optica Spectrum Disorder in a 2-Year-Old Child

"Leber hereditary optic neuropathy (LHON-Plus)" is a phenotype of LHON that is characterized by extraocular neurologic manifestations, which may be the first manifestations of the disease.

Effective treatment of choreaballism due to an MT-CYB variant with haloperidol, tetrabenazine, and antioxidants

Hypokinetic and hyperkinetic movement disorders are a common phenotypic feature of mitochondrial disorders. Choreaballism has been reported particularly in patients with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome and in maternally inherited diabetes and deafness syndrome. The pathophysiological basis of movement disorders in mitochondrial disorders is the involvement of the basal ganglia or the midbrain. Haloperidol and mitochondrial cocktails have proven beneficial in some of these cases. Here we present another patient with mitochondrial choreaballism who benefited significantly from symptomatic therapy. The patient is a 14-year-old male with a history of hypoacusis, ptosis, and focal tonic-clonic seizures of the upper/lower limbs on either side since childhood. Since this time he has also developed occasional, abnormal involuntary limb movements, choreaballism, facial grimacing, carpopedal spasms, and abnormal lip sensations. He was diagnosed with a non-syndromic mitochondrial disorder after detection of the variant m.15043G > A in MT-CYB. Seizures have been successfully treated with lamotrigine. Hypocalcemia was treated with intravenous calcium. For hypoparathyroidism calcitriol was given. Choreaballism was treated with haloperidol and tetrabenazine. In addition, he received coenzyme Q10, L-carnitine, thiamine, riboflavin, alpha-lipoic acid, biotin, vitamin-C, vitamin-E, and creatine-monohydrate. With this therapy, the choreaballism disappeared completely. This case shows that mitochondrial disorders can manifest with cognitive impairment, seizures, movement disorder, hypoacusis, endocrinopathy, cardiomyopathy, neuropathy, and myopathy, that choreaballism can be a phenotypic feature of multisystem mitochondrial disorders, and that choreaballism favorably responds to haloperidol, tetrabenazine, and possibly to a cocktail of antioxidants, cofactors, and vitamins.

Dystonia genes and their biological pathways

High-throughput sequencing has been instrumental in uncovering the spectrum of pathogenic genetic alterations that contribute to the etiology of dystonia. Despite the immense heterogeneity in monogenic causes, studies performed during the past few years have highlighted that many rare deleterious variants associated with dystonic presentations affect genes that have roles in certain conserved pathways in neural physiology. These various gene mutations that appear to converge towards the disruption of interconnected cellular networks were shown to produce a wide range of different dystonic disease phenotypes, including isolated and combined dystonias as well as numerous clinically complex, often neurodevelopmental disorder-related conditions that can manifest with dystonic features in the context of multisystem disturbances. In this chapter, we summarize the manifold dystonia-gene relationships based on their association with a discrete number of unifying pathophysiological mechanisms and molecular cascade abnormalities. The themes on which we focus comprise dopamine signaling, heavy metal accumulation and calcifications in the brain, nuclear envelope function and stress response, gene transcription control, energy homeostasis, lysosomal trafficking, calcium and ion channel-mediated signaling, synaptic transmission beyond dopamine pathways, extra- and intracellular structural organization, and protein synthesis and degradation. Enhancing knowledge about the concept of shared etiological pathways in the pathogenesis of dystonia will motivate clinicians and researchers to find more efficacious treatments that allow to reverse pathologies in patient-specific core molecular networks and connected multipathway loops.

Magnetic resonance imaging negative myelopathy in Leber's hereditary optic neuropathy: a case report

BACKGROUND

Leber's hereditary optic neuropathy (LHON) is a common form of mitochondrial disease. The typical clinical presentation of LHON is subacute, painless loss of vision resulting from bilateral optic nerve atrophy. Moreover, extra-ocular manifestations such as cardiac conduction abnormalities and neurological manifestations such as multiple sclerosis (MS) like disease or parkinsonism are encountered in some patients. Abnormal findings in spinal cord MR imaging or in the cerebrospinal fluid (CSF) have been observed in previous cases of LHON-associated myelopathy.

CASE PRESENTATION

We report a male patient with LHON who developed symptoms of myelopathy including gait unsteadiness, enhanced deep tendon reflexes and sensory loss of the lower extremities. Imaging of the brain and spinal cord, CSF analysis, as well as neurography and electromyography did not disclose any abnormalities. The somatosensory evoked potential (SEP) findings were suggestive of dorsal column dysfunction.

CONCLUSIONS

The patient case demonstrates that myelopathy associated with LHON can present without abnormal findings in central nervous system MR imaging or in the CSF, and without evidence suggestive of multiple sclerosis or MS-like disease. The dorsal column seems to be particularly vulnerable to myelopathy changes in LHON. Evoked potential investigations may assist in confirming the diagnosis, when clinical features are in line with myelopathy but findings in CSF analysis and central nervous system imaging are normal.

A Case of a 23-Year-Old Male With Leber Hereditary Optic Neuropathy With a Rare Mutation

Mitochondrial DNA (mtDNA) is responsible for encoding 13 subunits of the respiratory chain. These subunits are crucial in providing reducing equivalents for the energy-intensive intracellular processes. Leber hereditary optic neuropathy (LHON) is a mitochondrial illness that causes carcinogenesis due to oxidative stress and painless loss of central vision as a result of selective degradation of retinal ganglion cells as well as their axons. We present a case of a 23-year-old male patient who was diagnosed with subacute LHON. The mutation in our patient was found in a less commonly mutated exon sequence of MT-NDL4, which codes for NADH (nicotinamide adenine dinucleotide hydrogen, reduced) dehydrogenase subunit 4L. The MT-ND4L exon is located immediately upstream of the MTD4 exon on the human mtDNA. The take-home message is to always perform a comprehensive mitochondrial genome analysis for identifying rare mutations when LHON is suspected.

A novel TYMP mutation in a family with MNGIE syndrome: Molecular docking, dynamic simulation and computational investigations

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE; OMIM 603041) is a rare inherited metabolic disorder mostly caused by mutations in TYMP gene encoding thymidine phosphorylase (TP) protein that affects the mitochondrial nucleotide metabolism. TP, functionally active as a homodimer, is involved in the salvage pathway of pyrimidine nucleosides. MNGIE-like syndrome having an overlapping phenotype of MNGIE was also described and has been associated with mutations in POLG and RRM2B genes. In the present study, we report the molecular investigation of a consanguineous family including two patients with clinical features suggestive of MNGIE syndrome. Bioinformatics analyses were carried out in addition to mtDNA deletion screening and copy number quantification in the blood of the two patients. Whole exome sequencing and Sanger sequencing analyses revealed the segregation in the affected family a novel mutation c.1205T>A (p.L402Q) within the exon 9 of the TYMP gene. In addition, mtDNA analysis revealed the absence of mtDNA deletions and a decrease of the copy number in the blood of the two patients of the studied family. The p.Leu402Gln mutation was located in a conserved amino acid within the α/β domain of the TP protein and several software supported its pathogenicity. In addition, and based on docking and molecular dynamic simulation analyses, results revealed that L402Q caused a conformational change in TP mutated structure and could therefore alter its flexibility and stability. These changes prevent also the formation of stable homodimer leading to non-functional protein with partial or complete loss of its catalytic activity.

Whole mitochondrial genome sequencing of Malaysian patients with cardiomyopathy

Cardiomyopathy (CMP) constitutes a diverse group of myocardium diseases affecting the pumping ability of the heart. Genetic predisposition is among the major factors affecting the development of CMP. Globally, there are over 100 genes in autosomal and mitochondrial DNA (mtDNA) that have been reported to be associated with the pathogenesis of CMP. However, most of the genetic studies have been conducted in Western countries, with limited data being available for the Asian population. Therefore, this study aims to investigate the mutation spectrum in the mitochondrial genome of 145 CMP patients in Malaysia. Long-range PCR was employed to amplify the entire mtDNA, and whole mitochondrial genome sequencing was conducted on the MiSeq platform. Raw data was quality checked, mapped, and aligned to the revised Cambridge Reference Sequence (rCRS). Variants were named, annotated, and filtered. The sequencing revealed 1,077 variants, including 18 novel and 17 CMP and/or mitochondrial disease-associated variants after filtering. In-silico predictions suggested that three of the novel variants (m.8573G>C, m.11916T>A and m.11918T>G) in this study are potentially pathogenic. Two confirmed pathogenic variants (m.1555A>G and m.11778G>A) were also found in the CMP patients. The findings of this study shed light on the distribution of mitochondrial mutations in Malaysian CMP patients. Further functional studies are required to elucidate the role of these variants in the development of CMP.

Leber's Hereditary Optic Neuropathy Plus Causing Recurrent Myelopathy due to an MT-DN1 Mutation at G3635A

A 51-year-old man with known Leber's hereditary optic neuropathy (LHON) presented with worsening lower extremity weakness and numbness. Following an episode of myelopathy two years before, he had been ambulating with a walker but over two weeks became wheelchair bound. He also developed a sensory level below the T4 dermatome to light touch, pinprick, and vibration. MRI of his cervical and thoracic spine showed a nonenhancing T2 hyperintense lesion extending from C2 to T12. At his presentation two years earlier, he was found to have a longitudinally extensive myelopathy attributed to his LHON. Genetic testing revealed a 3635 guanine to adenine mutation. MRI at that presentation demonstrated a C1-T10 lesion involving the central and posterior cord but, unlike the new lesion, did not involve the ventral and lateral horns. Given the similarity to his prior presentation and a negative evaluation for alternative etiologies, he was thought to have recurrent myelopathy secondary to Leber's Plus. To our knowledge, recurrent myelopathy due specifically to the G3635A mutation in Leber's Plus has not been reported previously.

Mitochondrial Retinopathies

The retina is an exquisite target for defects of oxidative phosphorylation (OXPHOS) associated with mitochondrial impairment. Retinal involvement occurs in two ways, retinal dystrophy (retinitis pigmentosa) and subacute or chronic optic atrophy, which are the most common clinical entities. Both can present as isolated or virtually exclusive conditions, or as part of more complex, frequently multisystem syndromes. In most cases, mutations of mtDNA have been found in association with mitochondrial retinopathy. The main genetic abnormalities of mtDNA include mutations associated with neurogenic muscle weakness, ataxia and retinitis pigmentosa (NARP) sometimes with earlier onset and increased severity (maternally inherited Leigh syndrome, MILS), single large-scale deletions determining Kearns-Sayre syndrome (KSS, of which retinal dystrophy is a cardinal symptom), and mutations, particularly in mtDNA-encoded ND genes, associated with Leber hereditary optic neuropathy (LHON). However, mutations in nuclear genes can also cause mitochondrial retinopathy, including autosomal recessive phenocopies of LHON, and slowly progressive optic atrophy caused by dominant or, more rarely, recessive, mutations in the fusion/mitochondrial shaping protein OPA1, encoded by a nuclear gene on chromosome 3q29.

Genetic and Clinical Predictors of Ataxia in Pediatric Primary Mitochondrial Disorders

Evaluation of ataxia in children is challenging in clinical practice. This is particularly true for highly heterogeneous conditions such as primary mitochondrial disorders (PMD). This study aims to explore cerebellar and brain abnormalities identified on MRI as potential predictors of ataxia in patients with PMD and, likewise, to determine the effect of the patient's genetic profile on these predictors as well as determination of the temporal relationship of clinical ataxia with MRI findings. We evaluated clinical, radiological, and genetic characteristics of 111 PMD patients younger than 21 years of age at The Children's Hospital of Philadelphia. Data was extracted from charts. Blinded radiological evaluations were carried out by experienced neuroradiologists. Multivariate logistic regression and generalized equation estimates were used for analysis. Ataxia was identified in 41% of patients. Cerebellar atrophy or putaminal involvement with mitochondrial DNA (mtDNA) mutations (OR 1.18, 95% CI 1.1-1.3, p < 0.001) and nuclear DNA mutation with no atrophy of the cerebellum (OR 1.14, 95% CI 1.0-1.3, p = 0.007) predicted an increased likelihood of having ataxia per year of age. Central tegmental tract predicted the presence of ataxia independent of age and pathogenic variant origin (OR 9.8, 95% CI 2-74, p = 0.009). Ataxia tended to precede the imaging finding of cerebellar atrophy. Cerebellar atrophy and putaminal involvement on MRI of pediatric-onset PMD may predict the presence of ataxia with age in patients with mtDNA mutations. This study provides predicted probabilities of having ataxia per year of age that may help in family counseling and future research of the population.

Altered transcriptome and disease-related phenotype emerge only after fibroblasts harvested from patients with age-related macular degeneration are differentiated into retinal pigment epithelium

We have reported previously that retinal pigment epithelium (RPE) differentiated from induced pluripotent stem cells (iPSC) generated from fibroblasts of patients with age-related macular degeneration (AMD) exhibit a retinal degenerative disease phenotype and a distinct transcriptome compared to age-matched controls. Since the genetic composition of the iPSC and RPE are inherited from fibroblasts, we investigated whether differential behavior was present in the parental fibroblasts and iPSC prior to differentiation of the cell lines into RPE. Principal component analyses revealed significant overlap (essentially no differences) in the transcriptome of fibroblasts between AMD and controls. After reprogramming, there was no significant difference in the transcriptome of iPSC generated from AMD versus normal donors. In contrast, the transcriptome of RPE derived from iPSC segregated into two distinct clusters of AMD-derived cells versus controls. Interestingly, mitochondrial dysfunction in AMD-derived RPE was evident after approximately two months in culture. Moreover, these differences in mitochondrial dysfunction were not evident in the parental fibroblasts and iPSC. This study demonstrates an altered transcriptome and impaired mitochondrial function in RPE derived from AMD patients versus controls, and demonstrates these differences are not present in the original fibroblasts or iPSC. These results suggest that pathology in AMD is triggered upon differentiation of parent cells into RPE. More study of this phenomenon could advance the current understandings of the etiology of AMD and the development of novel therapeutic targets.

Mitochondrial DNA modification by CRISPR/Cas system: Challenges and future direction

CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats)/Cas (CRISPR associated endonuclease), a hotshot genome editing tool which is originally known to be the form of prokaryotic adaptive immune system against viral infections has gained all the attention of scientific community as a promising genome editing platform. This review encompasses a brief description of mitochondrial disease conditions associated with the alteration in mitochondrial genome (mtDNA) and highlights the key role of the CRISPR/Cas system pertaining to its working mechanism and its involvement in gene-based therapeutics in treating the foresaid mitochondrial diseases. Here, we also extend the perception related to the detailed mechanism of CRISPR/Cas system in mtDNA modification.

Clinical features of mtDNA-related syndromes in adulthood

Mitochondrial diseases are the most common inheritable metabolic diseases, due to defects in oxidative phosphorylation. They are caused by mutations of nuclear or mitochondrial DNA in genes involved in mitochondrial function. The peculiarity of "mitochondrial DNA genetics rules" in part explains the marked phenotypic variability, the complexity of genotype-phenotype correlations and the challenge of genetic counseling. The new massive genetic sequencing technologies have changed the diagnostic approach, enhancing mitochondrial DNA-related syndromes diagnosis and often avoiding the need of a tissue biopsy. Here we present the most common phenotypes associated with a mitochondrial DNA mutation with the recent advances in diagnosis and in therapeutic perspectives.

Oxidative Stress Profile in Genetically Confirmed Cases of Leber's Hereditary Optic Neuropathy

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.