Progressive external ophthalmoplegia - A case report.

Progressive external ophthalmoplegia is a slowly progressive hereditary mitochondrial myopathy. Most mitochondrial disorders overlap clinically, enzymatically, and genetically. The most common enzyme defect is the combined deficit of complexes I and IV. Progressive external ophthalmoplegia particularly affects the extraocular muscles and is characterised by ophthalmoplegia, and bilateral ptosis. The ptosis and ophthalmoplegia is unresponsive to anticholinergics, with no effective treatment, but corrective surgery for ptosis as a palliative one. In this article, we report a rare case of a 16-year-old female with characterstic histological features consistent with progressive external ophthalmoplegia.

A case of mitochondrial DNA depletion syndrome type 11 - expanding the genotype and phenotype.

Mitochondrial DNA depletion syndrome type 11 (MTDPS11) is caused by pathogenic variants in MGME1 gene. We report a woman, 40-year-old, who presented slow progressive drop eyelid at 11-year-old with, learning difficulty and frequent falls. Phisical examination revealed: mild scoliosis, elbow hyperextensibility, flat feet, chronic progressive external ophthalmoplegia with upper eyelid ptosis, diffuse hypotonia, and weakness of arm abduction and neck flexion. Investigation evidenced mild serum creatine kinase increase and glucose intolerance; second-degree atrioventricular block; mild mixed-type respiratory disorder and atrophy and granular appearance of the retinal pigment epithelium. Brain magnetic resonance showed cerebellar atrophy. Muscle biopsy was compatible with mitochondrial myopathy. Genetic panel revealed a homozygous pathogenic variant in the MGME1 gene, consistent with MTDPS11 (c.862C>T; p.Gln288*). This case of MTDPS11 can contribute to the phenotypic characterization of this ultra-rare mitochondrial disorder, presenting milder respiratory and nutritional involvement than the previously reported cases, with possible additional features.

Identification of two novel RRM2B variants associated with autosomal recessive progressive external ophthalmoplegia in a family with pseudodominant inheritance pattern.

RRM2B encodes the p53-inducible small subunit (p53R2) of ribonucleotide reductase, a key protein for mitochondrial DNA (mtDNA) synthesis. Pathogenic variants in this gene result in familial mitochondrial disease in adults and children, secondary to a maintenance disorder of mtDNA. This study describes two patients, mother and son, with early-onset chronic progressive external ophthalmoplegia (PEO). Skeletal muscle biopsy from the latter was examined: cytochrome c oxidase (COX)-negative fibres were shown, and molecular studies revealed multiple mtDNA deletions. A next-generation sequencing gene panel for nuclear-encoded mitochondrial maintenance genes identified two unreported heterozygous missense variants (c.514 G > A and c.682 G > A) in the clinically affected son. The clinically affected mother harboured the first variant in homozygous state, and the clinically unaffected father harboured the remaining variant in heterozygous state. In silico analyses predicted both variants as deleterious. Cell culture studies revealed that patients' skin fibroblasts, but not fibroblasts from healthy controls, responded to nucleoside supplementation with enhanced mtDNA repopulation, thus suggesting an in vitro functional difference in patients' cells. Our results support the pathogenicity of two novel RRM2B variants found in two patients with autosomal recessive PEO with multiple mtDNA deletions inherited with a pseudodominant pattern.

[Chronic progressive external ophthalmoplegia that could not be diagnosed by biceps muscle biopsy, but was genetically diagnosed by extraocular muscle biopsy].

A 48-year-old Japanese male experienced slowly progressive diplopia. He had no family history and was negative for the edrophonium chloride test. Blood analysis showed elevated lactic acid and pyruvic acid levels, suggesting mitochondrial disease. A muscle biopsy from the biceps brachii was performed, but no pathological or genetical mitochondrial abnormalities were detected. Subsequently, he underwent muscle plication for diplopia in which the right inferior rectus muscle was biopsied. Genetic examination of genomic DNA extracted from the extraocular muscle tissue revealed multiple mitochondrial gene deletions, with a heteroplasmy rate of approximately 35%, resulting in the diagnosis of chronic progressive external ophthalmoplegia. In mitochondrial diseases, the tissue distribution of mitochondria with disease-associated variants in mtDNA should be noted, and it is important to select the affected muscle when performing a biopsy for an accurate diagnosis.

Exophthalmos associated with chronic progressive external ophthalmoplegia.

PURPOSE: Chronic progressive external ophthalmoplegia (CPEO) is a mitochondrial disease characterized by slowly progressive ptosis and limitations in ocular motility. Although exophthalmos is not considered to be a common feature of CPEO, this study focused on the incidence of exophthalmos in patients with CPEO. STUDY DESIGN: Retrospective observational case series METHODS: We reviewed the clinical charts of patients who received a diagnosis of CPEO sometime during the period between January 2010 and December 2018. CPEO was diagnosed on the basis of detection of a deletion of mitochondrial DNA (mtDNA) from saliva, buccal mucosa, or extraocular muscle specimens obtained during strabismus surgery. Horizontal MRI/CT images or Hertel ophthalmometry was used in determining exophthalmos. RESULTS: Seven patients (4 males) were identified. The mean age at diagnosis was 32.6 years (range 13-53 years). mtDNA deletion mutations were detected in the buccal mucous membrane DNA in 5 patients and in the saliva and extraocular muscle DNA in 2 patients. MRI/CT was recorded in 6 patients, four of whom showed exophthalmos (cases 1-4), and case 5 was determined as exophthalmos on the basis of a Hertel ophthalmometer reading. Exophthalmos was bilateral in 4 of the patients (cases 1, 2, 4, and 5) and unilateral in 1 patient (case 3). Exophthalmos was the chief concern of 2 of the patients; however, it was not clinically significant in the other patients. CONCLUSIONS: Although exophthalmos may not be recognized by either the patient or the clinician, it may be one of the common features of CPEO. A large multiethnic study should be performed.

Progressive external ophthalmoplegia associated with novel MT-TN mutations.

OBJECTIVES: To describe two patients with progressive external ophthalmoplegia (PEO) and mitochondrial myopathy associated with mutations in mitochondrial DNA, encoding the tRNAAsn gene (MT-TN), which have not previously been published with clinical descriptions. MATERIALS & METHODS: Two unrelated patients with PEO were clinically examined. Muscle biopsy was performed and investigated by exome sequencing, enzyme histochemistry, and immunohistochemistry. The level of heteroplasmy was investigated in single muscle fibers and in other tissues. RESULTS: Patient 1 was a 52-year-old man with ptosis, PEO, and exercise intolerance since childhood. Muscle biopsy demonstrated mitochondrial myopathy with frequent cytochrome c oxidase (COX)-deficient fibers and a heteroplasmic mutation, m.5669G>A in the MT-TN gene, resulting in a substitution of a highly conserved C to T in the T stem of tRNAAsn . Patient 2 was a 66-year-old woman with ptosis, PEO, and exercise intolerance since many years. Muscle biopsy demonstrated mitochondrial myopathy with frequent COX-deficient fibers. She had a novel m.5702delA mutation in MT-TN, resulting in loss of a highly conserved U in the anticodon stem of tRNAAsn . Single fiber analysis in both cases showed highly significant differences in mutation load between COX-deficient and COX-normal fibers and a high threshold level for COX deficiency. The mutations were not found in blood, urine sediment or buccal cells. CONCLUSION: We describe two MT-TN mutations associated with PEO and mitochondrial myopathy, and their pathogenicity was demonstrated. Together with previous reports, the results indicate that MT-TN is a hot spot for mutations causing sporadic PEO.

A novel homozygous frameshift mutation in the DCC gene in a Pakistani family with autosomal recessive horizontal gaze palsy with progressive scoliosis-2 with impaired intellectual development.

Horizontal Gaze Palsy with Progressive Scoliosis-2 with Impaired Intellectual Development (HGPPS2) is a rare congenital disorder characterized by absence of conjugate horizontal eye movements, and progressive scoliosis developing in childhood and adolescence. We report three new patients with HGPPS2 in a consanguineous Pakistani family, presenting varying degrees of progressive scoliosis, developmental delays, horizontal gaze palsy, agenesis of corpus callosum, and absence of cerebral commissures. Analysis of genotyping data identified shared loss of heterozygosity (LOH) region on chromosomes 5p15.33-15.31, 6q11.2-12, and 18q21.1-21.3. A hypothesis-free, unbiased exome data analysis detected an insertion of nucleotide A (c.2399dupA) in exon 16 of the DCC gene. The insertion is predicted to cause frameshift p.(Asn800Lysfs*11). Interestingly, DCC gene is present in the LOH region on chromosome 18. Variant (c.2399dupA) in the DCC gene is considered as the most probable candidate variant for HGPPS2 based on the presence of DCC in the LOH region, previously reported role of DCC in HGPPS2, perfect segregation of candidate variant with the disease, prediction of variant pathogenicity, and absence of variant in variation databases. Sanger Sequencing confirmed the presence of the novel homozygous mutation in all three patients; the parents were heterozygous carriers of the mutation, in accordance with an autosomal recessive inheritance pattern. DCC encodes a netrin-1 receptor protein; its role in the development of the CNS has recently been established. Biallelic DCC mutations have previously been shown to cause HGPPS2. A novel homozygous variant in patients of the reported family extend the genotypic and phenotypic spectrum of HGPPS2.

Chronic Progressive External Ophthalmoplegia due to a Rare de novo m.12334G>A MT-TL2 Mitochondrial DNA Variant1.

We describe a patient with chronic progressive external ophthalmoplegia (CPEO) due to a rare mitochondrial genetic variant. Muscle biopsy revealed numerous cytochrome c oxidase (COX)-deficient fibres, prompting sequencing of the entire mitochondrial genome in muscle which revealed a rare m.12334G>A variant in the mitochondrial (mt-) tRNALeu(CUN)(MT-TL2) gene. Analysis of several tissues showed this to be a de novo mutational event. Single fibre studies confirmed the segregation of high m.12334G>A heteroplasmy levels with the COX histochemical defect, confirming pathogenicity of the m.12334G>A MT-TL2 variant. This case illustrates the importance of pursuing molecular genetic analysis in clinically-affected tissues when mitochondrial disease is suspected.

Clinical, pathological and genetic spectrum in 89 cases of mitochondrial progressive external ophthalmoplegia.

BACKGROUND: Mitochondrial progressive external ophthalmoplegia (PEO) encompasses a broad spectrum of clinical and genetic disorders. We describe the phenotypic subtypes of PEO and its correlation with molecular defects and propose a diagnostic algorithm. METHODS: Retrospective analysis of the clinical, pathological and genetic features of 89 cases. RESULTS: Three main phenotypes were found: 'pure PEO' (42%), consisting of isolated palpebral ptosis with ophthalmoparesis; Kearns-Sayre syndrome (10%); and 'PEO plus', which associates extraocular symptoms, distinguishing the following subtypes: : myopathic (33%), bulbar (12%) and others (3%). Muscle biopsy was the most accurate test, showing mitochondrial changes in 95%. Genetic diagnosis was achieved in 96% of the patients. Single large-scale mitochondrial DNA (mtDNA) deletion was the most frequent finding (63%), followed by multiple mtDNA deletions (26%) due to mutations in TWNK (n=8), POLG (n=7), TK2 (n=6) or RRM2B (n=2) genes, and point mtDNA mutations (7%). Three new likely pathogenic mutations were identified in the TWNK and MT-TN genes. CONCLUSIONS: Phenotype-genotype correlations cannot be brought in mitochondrial PEO. Muscle biopsy should be the first step in the diagnostic flow of PEO when mitochondrial aetiology is suspected since it also enables the study of mtDNA rearrangements. If no mtDNA deletions are identified, whole mtDNA sequencing should be performed.

Progressive External Ophthalmoplegia in Polish Patients-From Clinical Evaluation to Genetic Confirmation.

Mitochondrial encephalomyopathies comprise a group of heterogeneous disorders resulting from impaired oxidative phosphorylation (OxPhos). Among a variety of symptoms progressive external ophthalmoplegia (PEO) seems to be the most common. The aim of this study is to present clinical and genetic characteristics of Polish patients with PEO. Clinical, electrophysiological, neuroradiological, and morphological data of 84 patients were analyzed. Genetic studies of mitochondrial DNA (mtDNA) were performed in all patients. Among nuclear DNA (nDNA) genes POLG was sequenced in 41 patients, TWNK (C10orf2) in 13 patients, and RNASEH1 in 2 patients. Total of 27 patients were included in the chronic progressive external ophthalmoplegia (CPEO) group, 24 in the CPEO+ group. Twenty-six patients had mitochondrial encephalomyopathy (ME), six patients Kearns-Sayre syndrome (KSS), and one patient sensory ataxic neuropathy, dysarthria, ophthalmoparesis (SANDO) syndrome. Genetic analysis of nDNA genes revealed the presence of pathogenic or possibly pathogenic variants in the POLG gene in nine patients, the TWNK gene in five patients and the RNASEH1 gene in two patients. Detailed patients' history and careful assessment of family history are essential in the diagnostic work-up. Genetic studies of both mtDNA and nDNA are necessary for the final diagnosis of progressive external ophthalmoplegia and for genetic counseling.

A PRIMPOL mutation and variants in multiple genes may contribute to phenotypes in a familial case with chronic progressive external ophthalmoplegia symptoms.

Chronic progressive external ophthalmoplegia (CPEO) is one of the most common mitochondrial disorders. It is characterized by bilateral, slowly progressing loss of extraocular muscle mobility, orbicularis oculi weakness, ptosis, and other neuromuscular symptoms, which are caused by the accumulation of multiple mitochondrial DNA (mtDNA) deletions. Many mutations in different nuclear genes, such as POLG1, POLG2, ANT1, and others, have been described as causing autosomal-inherited CPEO with multiple mtDNA deletions. Most causative genes are involved in mtDNA replication impairment. Here, we report a family with CPEO-like symptoms characterized by multiple muscle mtDNA deletions, ptosis, diabetes, hearing loss, mental retardation, and emotional instability. We performed genetic analyses to identify nuclear gene mutations in the family. DNA from the proband was analyzed by whole-exome sequencing. In addition to possible pathogenic mutations, rare variants were prioritized for gene-functional phenotype interpretation. We found possible pathogenetic mutations in the PRIMPOL, BRCA1, CPT2, and GJB2 genes, and functional polymorphisms in the CARD8, and MEFV genes. Multiple functional polymorphisms and possible pathogenic mutations may contribute to mitochondrial-disease-like phenotypes in a composite manner.

A novel mitochondrial m.4414T>C MT-TM gene variant causing progressive external ophthalmoplegia and myopathy.

We report a novel mitochondrial m.4414T>C variant in the mt-tRNAMet (MT-TM) gene in an adult patient with chronic progressive external ophthalmoplegia and myopathy whose muscle biopsy revealed focal cytochrome c oxidase (COX)-deficient and ragged red fibres. The m.4414T>C variant occurs at a strongly evolutionary conserved sequence position, disturbing a canonical base pair and disrupting the secondary and tertiary structure of the mt-tRNAMet. Definitive evidence of pathogenicity is provided by clear segregation of m.4414T>C mutant levels with COX deficiency in single muscle fibres. Interestingly, the variant is present in skeletal muscle at relatively low levels (30%) and undetectable in accessible, non-muscle tissues from the patient and her asymptomatic brother, emphasizing the continuing requirement for a diagnostic muscle biopsy as the preferred tissue for mtDNA genetic investigations of mt-tRNA variants leading to mitochondrial myopathy.

Different mitochondrial genetic defects exhibit the same protein signature of metabolism in skeletal muscle of PEO and MELAS patients: A role for oxidative stress.

A major challenge in mitochondrial diseases (MDs) is the identification of biomarkers that could inform of the mechanisms involved in the phenotypic expression of genetic defects. Herein, we have investigated the protein signature of metabolism and of the antioxidant response in muscle biopsies of clinically and genetically diagnosed patients with Progressive External Ophthalmoplegia due to single large-scale (PEO-sD) or multiple (PEO-mD) deletions of mtDNA and Mitochondrial Encephalopathy Lactic Acidosis and Stroke-like episode (MELAS) syndrome, and healthy donors. A high-throughput immunoassay technique that quantitates the expression of relevant proteins of glycolysis, glycogenolysis, pentose phosphate pathway, oxidative phosphorylation, pyruvate and fatty acid oxidation, tricarboxylic acid cycle and the antioxidant response in two large independent and retrospectively collected cohorts of PEO-sD, PEO-mD and MELAS patients revealed that despite the heterogeneity of the genetic alterations, the three MDs showed the same metabolic signatures in both cohorts of patients, which were highly divergent from those of healthy individuals. Linear Discriminant Analysis and Support Vector Machine classifier provided a minimum of four biomarkers to discriminate healthy from pathological samples. Regardless of the induction of a large number of enzymes involved in ameliorating oxidative stress, the down-regulation of mitochondrial superoxide dismutase (SOD2) and catalase expression favored the accumulation of oxidative damage in patients' proteins. Down-regulation of SOD2 and catalase expression in MD patients is not due to relevant changes in the availability of their mRNAs, suggesting that oxidative stress regulates the expression of the two enzymes post-transcriptionally. We suggest that SOD2 and catalase could provide specific targets to improve the detoxification of reactive oxygen species that affects muscle proteins in these patients.

Topoisomerase 3α Is Required for Decatenation and Segregation of Human mtDNA.

How mtDNA replication is terminated and the newly formed genomes are separated remain unknown. We here demonstrate that the mitochondrial isoform of topoisomerase 3α (Top3α) fulfills this function, acting independently of its nuclear role as a component of the Holliday junction-resolving BLM-Top3α-RMI1-RMI2 (BTR) complex. Our data indicate that mtDNA replication termination occurs via a hemicatenane formed at the origin of H-strand replication and that Top3α is essential for resolving this structure. Decatenation is a prerequisite for separation of the segregating unit of mtDNA, the nucleoid, within the mitochondrial network. The importance of this process is highlighted in a patient with mitochondrial disease caused by biallelic pathogenic variants in TOP3A, characterized by muscle-restricted mtDNA deletions and chronic progressive external ophthalmoplegia (CPEO) plus syndrome. Our work establishes Top3α as an essential component of the mtDNA replication machinery and as the first component of the mtDNA separation machinery.

[Chronic Progressive External Ophthalmoplegia Ptosis: Problems with Diagnostics and Treatment]. / Ptosis bei chronisch progressiver externer Ophthalmoplegie: diagnostische Probleme und therapeutische Konsequenzen.

Ptosis is often the first symptom of chronic progressive external ophthalmoplegia (CPEO), a rare muscle disorder. As the disease progresses, it can lead to ocular motility defects. Ptosis is present in the early stages of the disease and can be corrected by levator surgery. Due to the rarity of CPEO (< 1% of ptosis patients), further diagnostic steps with muscle biopsy and genetic analysis of mitochondrial DNA are usually not considered in the early phase. Intraoperative abnormal observations during ptosis surgery and postoperative motility problems are signs of CPEO. If CPEO is confirmed, alternative surgical methods can correct the ptosis, like frontalis suspension.

Focal Segmental Glomerulosclerosis Associated with Chronic Progressive External Ophthalmoplegia and Mitochondrial DNA A3243G Mutation.

Focal segmental glomerulosclerosis (FSGS) is caused by various etiologies, with mitochondrial dysfunction being one of the causes. FSGS is known to be associated with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), which is a subclass of mitochondrial disease. However, it has rarely been reported in other mitochondrial disease subclasses. Here, we reported a 20-year-old man diagnosed with FSGS associated with chronic progressive external ophthalmoplegia (CPEO) due to mitochondrial DNA (mtDNA) 3243A>G mutation. He presented with left ptosis, short stature, mild sensorineural deafness, and cardiac conduction block. A renal biopsy sample showed segmental sclerosis and adhesions between capillaries and Bowman's capsule, indicating FSGS. Electron microscopy demonstrated abnormal aggregated mitochondria in podocytes, and the basement membrane and epithelial cells of Bowman's capsule. Skeletal muscle biopsy also showed accumulation of abnormal mitochondria. mtDNA analysis identified heteroplasmic mtDNA 3243A>G mutation with no large-scale deletions. From these findings, we diagnosed the case as CPEO with multi-organ involvement including FSGS. Our report demonstrates that CPEO, as well as MELAS, can be associated with FSGS. Because mitochondrial disease presents with a variety of clinical symptoms, atypical cases with non-classical manifestations are observed. Thus, mitochondrial disease should be considered as an underlying cause of FSGS with systemic manifestations even with atypical phenotypes.

MtDNA-maintenance defects: syndromes and genes.

A large group of mitochondrial disorders, ranging from early-onset pediatric encephalopathic syndromes to late-onset myopathy with chronic progressive external ophthalmoplegia (CPEOs), are inherited as Mendelian disorders characterized by disturbed mitochondrial DNA (mtDNA) maintenance. These errors of nuclear-mitochondrial intergenomic signaling may lead to mtDNA depletion, accumulation of mtDNA multiple deletions, or both, in critical tissues. The genes involved encode proteins belonging to at least three pathways: mtDNA replication and maintenance, nucleotide supply and balance, and mitochondrial dynamics and quality control. In most cases, allelic mutations in these genes may lead to profoundly different phenotypes associated with either mtDNA depletion or multiple deletions.

Clinical, biochemical, molecular, and histological features of 65 Portuguese patients with mitochondrial disorders.

INTRODUCTION: Mitochondrial disorders display remarkable genetic and phenotypic heterogeneity. METHODS: We performed a retrospective analysis of the clinical, histological, biochemical, and genetic features of 65 patients with molecular diagnoses of mitochondrial disorders. RESULTS: The most common genetic diagnosis was a single large-scale mitochondrial DNA (mtDNA) deletion (41.5%), and the most frequent clinical phenotype was chronic progressive external ophthalmoplegia (CPEO). It occurred in 41.5% of all patients, primarily in those with mtDNA deletions. Histological signs of mitochondrial dysfunction were found in 73.8% of patients, and respiratory chain enzyme assay (RCEA) abnormalities were detected in 51.9%. CONCLUSIONS: This study confirms the high relative frequency of single large-scale deletions among mitochondrial disorders as well as its particular association with CPEO. Muscle histology seems to be particularly useful in older patients and those with mtDNA deletions, whereas RCEA might be more helpful in young children or individuals with mtDNA depletion. Muscle Nerve 56: 868-872, 2017.

Mitochondrial mutations in 12S rRNA and 16S rRNA presenting as chronic progressive external ophthalmoplegia (CPEO) plus: A case report.

RATIONALE: Chronic progressive external ophthalmoplegia (CPEO) is a classical mitochondrial ocular disorder characterized by bilateral progressive ptosis and ophthalmoplegia. Kearns -Sayre syndrome (KSS) is a multisystem disorder with PEO, cardiac conduction block, and pigmentary retinopathy. A few individuals with CPEO have other manifestations of KSS, but do not meet all the clinical diagnosis criteria, and this is called "CPEO plus." PATIENT CONCERNS: We report a 48-year-old woman exhibiting limb weakness, ptosis, ophthalmoparesis, and cerebellar dysfunctions. DIAGNOSES: The patient was diagnosed as exhibiting CPEO plus syndrome. INTERVENTIONS: The patient underwent clinical, genetic, histological, and histochemical analysis. She was treated orally with CoQ10, vitamin Bs, L-carnitine, and vitamin E. OUTCOMES: The patient's serum creatine kinase levels, electrocardiography, and nerve conduction study results were normal; an electromyogram revealed myopathic findings. Magnetic resonance imaging showed global brain atrophy, particularly in the brainstem and cerebellum areas. A muscle biopsy showed the presence of abundant ragged red fibers. Sequencing of the mitochondrial DNA from the skeletal muscle biopsy revealed C960del mutation in 12S rRNA and homozygous mutation C2835T in 16S rRNA. She took medicines on schedule, the clinical features were similar as 2 years ago. LESSONS: This is the first report of 2 rRNA mutations in a patient with MRI findings showing global brain atrophy, particularly in brainstem and cerebellum areas. Early recognition and appropriate treatment is crucial. This case highlights the cerebellar ataxia can occur in CPEO plus.

Progressive External Ophthalmoplegia.

Progressive external ophthalmoplegia (PEO), marked by progressive bilateral ptosis and diffuse reduction in ocular motility, represents a finding of mitochondrial myopathy rather than a true diagnosis. PEO often occurs with other systemic features of mitochondrial dysfunction that can cause significant morbidity and mortality. Accurate and early recognition of PEO is paramount for the optimal care of these patients. We present an evidence-based review of the presenting neuro-ophthalmic features, differential diagnosis, diagnostic tools, systemic implications, and treatment options for isolated PEO and other PEO-associated mitochondrial syndromes.