Progressive cerebral vascular degeneration with mitochondrial encephalopathy

Molecular and neurological features of MELAS syndrome in paediatric patients: A case series and review of the literature

Background

Mitochondrial encephalomyopathy, lactic acidosis and stroke‐like episodes (MELAS) syndrome is one of the most well‐known mitochondrial diseases, with most cases attributed to m.3243A>G. MELAS syndrome patients typically present in the first two decades of life with a broad, multi‐systemic phenotype that predominantly features neurological manifestations––stroke‐like episodes. However, marked phenotypic variability has been observed among paediatric patients, creating a clinical challenge and delaying diagnoses.

Methods

A literature review of paediatric MELAS syndrome patients and a retrospective analysis in a UK tertiary paediatric neurology centre were performed.

Results

Three children were included in this case series. All patients presented with seizures and had MRI changes not confined to a single vascular territory. Blood heteroplasmy varied considerably, and one patient required a muscle biopsy. Based on a literature review of 114 patients, the mean age of presentation is 8.1 years and seizures are the most prevalent manifestation of stroke‐like episodes. Heteroplasmy is higher in a tissue other than blood in most cases.

Conclusion

The threshold for investigating MELAS syndrome in children with suspicious neurological symptoms should be low. If blood m.3243A>G analysis is negative, yet clinical suspicion remains high, invasive testing or further interrogation of the mitochondrial genome should be considered.

Major cerebral vessels involvement in patients with MELAS syndrome: Worth a scan? A systematic review

Major cerebral vessels have been proposed as a target of defective mitochondrial metabolism in patients with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes syndrome (MELAS). Cerebral angiographic techniques are not routinely performed in MELAS patients. A systematic literature review was performed to identify studies describing major vessel caliber alterations in MELAS. Twenty-three studies reporting on 46 MELAS patients were included. Alterations in major caliber vessels were present in 59% (27/46) of patients. Dilation occurred in 37% (17/46) of patients, and in 88% (15/17) of them during a stroke-like episode (SLE). Stenosis was reported in 24% (11/46) of patients: 36% (4/11) related to an SLE and 64% (7/11) to dissections or degenerative changes. During an SLE, identification of intracranial vessels dilation or stenosis could be a selection tool for new treatment protocols. Outside SLE, identification of major cerebral vessels dissections and degenerative changes may help to prevent subsequent complications.

Atherosclerosis Can Be Mitochondrial: A Review

One of the systems that are potentially affected in mitochondrial disorders, but hardly get systematically investigated, are the arteries. One of the phenotypic manifestations in arteries is atherosclerosis. This review focuses on the current knowledge and recent advances of mitochondrial atherosclerosis. We conducted a systematic literature review via PubMed using appropriate search terms.

Atherosclerosis in mitochondrial disorders may result from a primary pathomechanism or a secondary one due to mitochondrial diabetes, arterial hypertension, or hyperlipidemia. Anecdotal reports show that primary atherosclerosis can be a phenotypic feature of mitochondrial disorders. Predominantly, patients carrying mutations in mtDNA-located genes may develop primary mitochondrial atherosclerosis. Though not systematically investigated, it is conceivable that primary mitochondrial atherosclerosis results from increased oxidative stress, mitophagy, metabolic breakdown, or lactic acidosis. Mitochondrial disorder patients with primary mitochondrial atherosclerosis should receive not only antithrombotic medication but also antioxidants and cofactors.

Atherosclerosis in mitochondrial disorders may occur even in the absence of classical atherosclerosis risk factors, suggesting that atherosclerosis can be a primary manifestation of the metabolic defect. Though primary atherosclerosis in mitochondrial disorders has not been systematically investigated, anecdotal data indicate that mitochondrial dysfunction can be a mechanism for the development of primary, mitochondrial atherosclerosis. These patients require antioxidants and cofactors in addition to antithrombotic medication.

Cerebral imaging in paediatric mitochondrial disorders

OBJECTIVES

Because the central nervous system (CNS) is the second most frequently affected organ in mitochondrial disorders (MIDs) and since paediatric MIDs are increasingly recognised, it is important to know about the morphological CNS abnormalities on imaging in these patients. This review aims at summarising and discussing current knowledge and recent advances concerning CNS imaging abnormalities in paediatric MIDs.

METHODS

A systematic literature review was conducted.

RESULTS

The most relevant CNS abnormalities in paediatric MIDs on imaging include white and grey matter lesions, stroke-like lesions as the morphological equivalent of stroke-like episodes, cerebral atrophy, calcifications, optic atrophy, and lactacidosis. Because these CNS lesions may be seen with or without clinical manifestations, it is important to screen all MID patients for cerebral involvement. Some of these lesions may remain unchanged for years whereas others may be dynamic, either in the sense of progression or regression. Typical dynamic lesions are stroke-like lesions and grey matter lesions. Clinically relevant imaging techniques for visualisation of CNS abnormalities in paediatric MIDs are computed tomography, magnetic resonance (MR) imaging, MR spectroscopy, single-photon emission computed tomography, positron-emission tomography, and angiography.

CONCLUSIONS

CNS imaging in paediatric MIDs is important for diagnosing and monitoring CNS involvement. It also contributes to the understanding of the underlying pathomechanisms that lead to CNS involvement in MIDs.

MELAS and macroangiopathy: A case report and literature review

RATIONALE

Mitochondrial encephalopathy, lactic acidosis and stroke-like episodes (MELAS) are thought to be rarely accompanied by macroangiopathy. We reported a case of MELAS that presented right distal internal carotid arterial (ICA) stenosis and reviewed 12 similar previously reported cases involving intracranial large blood vessels.

PATIENT CONCERNS

A 38-year-old man suffered from recurrent stroke-like episodes (SE) such as alternating hemiparesis (right lesion 3 years ago and current left lesion), cortical blindness and seizure for 3 years, and was previously misdiagnosed as cerebral infarction. Magnetic Resonance Angiography (MRA) and Digital Subtraction Angiography (DSA) revealed right distal ICA stenosis and sparse cortex blood vessels, which were related to the previous SE.

DIAGNOSES

He was diagnosed by genetic screening (a mitochondrial DNA A3243G point mutation) and presence of high lactic acidosis (4.03 mmol/L), which rose to 7.8 mmol/L after exercise.

INTERVENTION

The patient received Coenzyme Q10, vitamin C, L-arginine for 2 weeks and valproic acid sodium (400 mg bid) to prevent seizures till now.

OUTCOMES

He is currently less active and intelligent than his peers, with occasional seizures, and needs family care.

LESSONS

Till date, there are 12 reported cases of MELAS combined with major cerebral arteries abnormalities including stenosis, dissection, occlusion, reversible vasoconstriction, aneurysms, and atherosclerosis. Hence, macroangiopathy in MELAS is not very rare. There is correlation between the affected vessels and the lesions in some cases, but not in others, which may increase the misdiagnosis rate. Hence, mitochondrial diseases cannot be excluded due to concurrent macroangiopathic lesions.

Mitochondrial DNA 3243A>T mutation in a patient with MELAS syndrome

Approximately 80% of cases of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) harbor a heteroplasmic m.3243A>G transition in the tRNA^{Leu (UUR)} (MTTL1) gene. We report a MELAS case with a rare heteroplasmic m.3243A>T mutation found by direct sequencing of MTTL1. This mutation has been previously reported in 5 cases, of which 2 cases had the MELAS phenotype. Our case also strengthens the hypothesis that the m.3243A>T mutation can cause the MELAS phenotype.

Mitochondrial m.3243A > G mutation and carotid artery dissection

The common m.3243A > G mutation of the mitochondrial DNA tRNALeu (UUR) gene is a maternally inherited mutation causing a wide spectrum of neurological and multisystemic disorders, including MELAS, characterized by recurrent cerebral infarction from young age. Vascular pathology in mitochondrial diseases has been described for small vessels, while large vessels involvement in mitochondrial diseases is considered rare.

Here we report two female patients harboring the m.3243A > G mutation, in whom the diagnosis of mitochondrial disease was made after acute dissection of the internal carotid arteries. Our cases expand the clinical spectrum of this mutation, and support the idea of large vessels vasculopathy due to impaired mitochondrial function in the vessel wall that may lead to arterial wall weakness. Thus, stroke in mitochondrial diseases could also be related to large vessels disease, but further studies are strongly needed. Moreover, mitochondrial aetiology should be kept in mind in patients with large vessel dissection, especially in those with additional mitochondrial red flags.

Unusual association between lysinuric protein intolerance and moyamoya vasculopathy

INTRODUCTION

Lysinuric protein intolerance (LPI) is a form of inherited aminoaciduria caused by a deficiency in the cationic amino acid transport process on the basolateral membrane of enterocytes and renal tubular cells. Clinical signs include gastrointestinal symptoms, failure to thrive, hepatosplenomegaly, osteoporosis, episodes of coma, intellectual deficiency, lung and renal involvement, bone marrow abnormalities, as well as altered immune response. Moyamoya disease is a cerebrovascular disorder predisposing sufferers to stroke through progressive stenosis of the intracranial internal carotid arteries and their proximal branches. Patients with characteristic moyamoya vasculopathy who also exhibit well-recognized associated conditions, such as Down syndrome or sickle-cell disease, are diagnosed with moyamoya syndrome, whereas those with no known associated risk factors are said to suffer from moyamoya disease.

CASE STUDY

A 5-year-old girl exhibiting aversion to protein-rich food and splenomegaly presented with a history of recurrent ischemic strokes. Cerebral angiography confirmed moyamoya vasculopathy. Metabolic investigation revealed abnormalities characteristic of LPI. This diagnosis was confirmed by the detection of a mutation within the SLC7A7 gene upon molecular investigation.

CONCLUSION

To the best of our knowledge, this is the first reported case of an association between moyamoya vasculopathy and LPI. While the question of association or coincidence cannot yet be answered, several pathophysiological consequences of LPI can be defined as separate, such as links between the impact of low arginine levels on the function of vascular endothelium and brain nitric oxide metabolism, as well as hemophagocytic syndrome associated with the risk of vasculitis, thus accounting for the development of moyamoya vasculopathy.

Central Nervous System Imaging in Mitochondrial Disorders

Imaging of central-nervous-system (CNS) abnormalities is important in patients with mitochondrial disorders (MCDs) since the CNS is the organ second most frequently affected in MCDs and some of them are potentially treatable. Clinically relevant imaging techniques for visualization of CNS abnormalities in MCDs are computed tomography, magnetic resonance imaging, and MR-spectroscopy. The CNS abnormalities in MCDs visualized by imaging techniques include stroke-like lesions with cytotoxic or vasogenic edema, laminar cortical necrosis, basal ganglia necrosis, focal or diffuse white matter lesions, focal or diffuse atrophy, intra-cerebral calcifications, cysts, lacunas, hypometabolisation, lactacidosis, hemorrhages, cerebral hypo- or hyperperfusion, intra-cerebral artery stenoses, or moyamoya syndrome. The CNS lesions may proceed with or without clinical manifestations, why neuroimaging should be routinely carried out in all MCDs to assess the degree of CNS involvement. Some of these lesions may remain unchanged for years, some may show contiguous spread and progression, but some may even disappear, spontaneously or in response to medication. Dynamics of Stroke-like lesions may be positively influenced by L-arginine, dichloracetate, steroids, edavarone, or antiepileptics. Symptomatic treatment of CNS abnormalities in MCD patients may positively influence their outcome.

Exercise-induced myalgia and rhabdomyolysis in a patient with the rare m.3243A>T mtDNA mutation

Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes comprises a number of mitochondrial disorders with a wide range of clinical presentations. We present the case of a 32-year-old patient with an m.3243A>T mitochondrial DNA mutation who presented with rhabdomyolysis after 2 days of excessive physical work. The case presented here demonstrates a new clinical phenotype associated with this pathogenic mtDNA mutation.

Mitochondrial dysfunction and mitochondrial DNA mutations in atherosclerotic complications in diabetes

Mitochondrial DNA (mtDNA) is particularly prone to oxidation due to the lack of histones and a deficient mismatch repair system. This explains an increased mutation rate of mtDNA that results in heteroplasmy, e.g., the coexistence of the mutant and wild-type mtDNA molecules within the same mitochondrion. In diabetes mellitus, glycotoxicity, advanced oxidative stress, collagen cross-linking, and accumulation of lipid peroxides in foam macrophage cells and arterial wall cells may significantly decrease the mutation threshold required for mitochondrial dysfunction, which in turn further contributes to the oxidative damage of the diabetic vascular wall, endothelial dysfunction, and atherosclerosis.

The genetics of white matter lesions

White matter lesions (WMLs), commonly seen as hyperintensities on T2-weighted MRI scans of healthy elderly individuals, are considered to be related to small vessel disease in the brain, and are often associated with subtle cognitive and functional impairments. WMLs also show a strong correlation with a wide range of neurodegenerative and neuropsychiatric disorders. Although a number of vascular risk factors for WMLs have been identified, genetic factors are also important with twin and family studies reporting high heritability. Mutations in several genes have been described that lead to monogenic disorders manifesting WMLs, such as Fabry disease and CADASIL. Because most individuals with WMLs do not have Mendelian disorders, most of the focus has been on single nucleotide polymorphisms as genetic risk markers for WMLs, either directly or through their interactions with other genes or medical risk factors. Candidate genes examined to date include those involved in cholesterol regulation and atherosclerosis, hypertension, neuronal repair, homocysteine levels, and oxidative stress pathways. In addition, although there have been a few genome-wide linkage studies, only one genome-wide association study has been performed. The majority of the genetic findings need independent replication, and studies need to be extended to other candidate genes. Collaborative efforts to examine genome-wide associations in large samples of both sexes of a broad age range using longitudinal studies are necessary. The identification of individuals genetically at risk of developing white matter lesions will have important implications for recognizing the etiology of WMLs and thereby developing clinical intervention strategies for their prevention.

The pathogenic m.3243A>T mitochondrial DNA mutation is associated with a variable neurological phenotype

The m.3243A>G point mutation in the mitochondrial tRNA(Leu(UUR)) (MTTL1) gene is a common cause of mitochondrial DNA disease and is associated with a variety of clinical presentations. A different mutation occurring at the same site - an m.3243A>T transversion - is less prevalent, but has previously been observed in two patients with encephalopathy and lactic acidosis. We report the investigations of a further two patients with the m.3243A>T mutation who presented with either a chronic progressive external ophthalmoplegia (CPEO) phenotype or sensorineural hearing loss, with single fibre mutation studies confirming segregation of the m.3243A>T mutation with COX deficiency.

Pathophysiology of stroke-like episodes in MELAS: neuron–astrocyte uncoupling in neuronal hyperexcitability

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) is a distinct clinical syndrome characterized by fluctuated encephalopathy, migraineous headache, seizure and stroke-like episodes. The molecular mechanism of MELAS mutations has been elucidated; however, the pathogenesis of stroke-like episodes remains largely unknown. Three main hypotheses include ischemic, metabolic and neuronal hyperexcitability hypotheses. Recently, emerging hypotheses include alterations in nitric oxide homeostasis and over-reduction/oxidative stress mechanisms. Although neuron–astrocyte communication is crucial in various physiological functions, it has not been seriously considered in the pathophysiology of stroke-like episodes. This review summarizes what is known about the molecular mechanisms of gene mutation, clinico-radiological, clinico-physiological and pathological features of stroke-like episodes, as well as its pathogenesis. We finally discuss potential mechanisms involved in the pathogenesis of stroke-like episodes based on currently available clinical data and the current understanding of the mechanisms of neuron–astrocyte communications. We propose that neuron–astrocyte uncoupling is a new target of research in mitochondrial disorders.

Clinical outcome after 450 revascularization procedures for moyamoya disease

Object

Moyamoya disease (MMD) is a rare cerebrovascular disease mainly described in the Asian literature. To address a lack of data on clinical characteristics and long-term outcomes in the treatment of MMD in North America, the authors analyzed their experience at Stanford University Medical Center. They report on a consecutive series of patients treated for MMD and detail their demographics, clinical characteristics, and long-term surgical outcomes.

Methods

Data obtained in consecutive series of 329 patients with MMD treated microsurgically by the senior author (G.K.S.) between 1991 and 2008 were analyzed. Demographic, clinical, and surgical data were prospectively gathered and neurological outcomes assessed in postoperative follow-up using the modified Rankin Scale. Association of demographic, clinical, and surgical data with postoperative outcome was assessed by chi-square, uni- and multivariate logistic regression, and Kaplan-Meier survival analyses.

Results

The authors treated a total of 233 adult patients undergoing 389 procedures (mean age 39.5 years) and 96 pediatric patients undergoing 168 procedures (mean age 10.1 years). Direct revascularization technique was used in 95.1% of adults and 76.2% of pediatric patients. In 264 patients undergoing 450 procedures (mean follow-up 4.9 years), the surgical morbidity rate was 3.5% and the mortality rate was 0.7% per treated hemisphere. The cumulative 5-year risk of perioperative or subsequent stroke or death was 5.5%. Of the 171 patients presenting with a transient ischemic attack, 91.8% were free of transient ischemic attacks at 1 year or later. Overall, there was a significant improvement in quality of life in the cohort as measured using the modified Rankin Scale (p < 0.0001).

Conclusions

Revascularization surgery in patients with MMD carries a low risk, is effective at preventing future ischemic events, and improves quality of life. Patients in whom symptomatic MMD is diagnosed should be offered revascularization surgery.

Pathophysiology and genetic factors in moyamoya disease

Moyamoya disease is an uncommon cerebrovascular condition characterized by progressive stenosis of the bilateral internal carotid arteries with compensatory formation of an abnormal network of perforating blood vessels providing collateral circulation. The etiology and pathogenesis of moyamoya disease remain unclear. Evidence from histological studies, proteomics, and endothelial progenitor cell analyses suggests new theories underlying the cause of vascular anomalies, including moyamoya disease. Familial moyamoya disease has been noted in as many as 15% of patients, indicating an autosomal dominant inheritance pattern with incomplete penetrance. Genetic analyses in familial moyamoya disease and genome-wide association studies represent promising strategies for elucidating the pathophysiology of this condition. In this review, the authors discuss recent studies that have investigated possible mechanisms underlying the etiology of moyamoya disease, including stem cell involvement and genetic factors. They also discuss future research directions that promise not only to offer new insights into the origin of moyamoya disease but to enhance our understanding of new vessel formation in the CNS as it relates to stroke, vascular anomalies, and tumor growth.

Progressive carotid artery stenosis with a novel tRNA phenylalanine mitochondrial DNA mutation

Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) is a distinct clinical syndrome caused by mutations in the mitochondrial DNA. The pathogenesis of stroke-like episodes remains unknown but major vessels stenosis is not a cause of stroke-like episodes. We describe a novel heteroplasmic G617A transition in the mitochondrial transfer RNA phenylalanine gene in a patient with encephalomyopathy who presented with recurrent embolic ischemic strokes accompanied by transient occlusion of middle cerebral, anterior cerebral and internal carotid arteries. These ischemic strokes were presumed to be artery-to artery embolisms associated with carotid artery stenosis. Single muscle fiber analysis revealed the pathogenicity of the mutation although its causative role on carotid artery stenosis remains to be elucidated. This case expands phenotypic spectrum of mitochondrial disorders in terms of macroangiopathy, but macroangiopathy-related ischemic strokes should be distinguished from classic stroke-like episodes of MELAS that are speculated to be microangioapthy-related or non-ischemic neurovascular events.