Neuro-ophthalmology of mitochondrial diseases:

Phenotypic heterogeneity of the mitochondrial DNA A8344G variant presenting with dorsal midbrain syndrome

Purpose

To describe a neuro-ophthalmic presentation of a phenotypically heterogeneous mitochondrial DNA variant.

Observations

A 10-year-old female with gross motor developmental delay, absence seizures and ataxia subacutely developed poor near acuity and asthenopia. She was found to have accommodative insufficiency, impaired supraduction and convergence retraction nystagmus leading to a diagnosis of dorsal midbrain syndrome. Brain MRI showed highly symmetrical lesions involving the dorsal pons. Genetic testing revealed a previously undiagnosed mitochondrial DNA (mtDNA) pathogenic variant, adenine to guanine at nucleopeptide pair 8344 (A8344G).

Conclusion and importance

The authors describe a unique, neuro-ophthalmic manifestation of mitochondrial disease in a pediatric patient. This report discusses the phenotypic heterogeneity of the mtDNA A8344G variant, which may include 'stroke-like episodes' involving the brainstem, thus presenting with ophthalmic manifestations.

Retinal disease in the neurology clinic

PURPOSE OF REVIEW

Retinal disease can manifest with visual symptoms similar to those which result from central nervous system disorders. We provide a framework for considering retinal causes of common visual complaints presenting to a neurology clinic.

RECENT FINDINGS

Technological advances have afforded quicker detection and a more thorough understanding of these retinal entities and are crucial to consider when evaluating visual complaints in the neurology clinic.

SUMMARY

It is essential to maintain a working knowledge of common retinal conditions that symptomatically overlap with common neurologic conditions. Furthermore, the ophthalmoscopic exam and retinal imaging modalities can both aid in the diagnosis and workup of visual complaints and neurologic disease.

Ophthalmological characteristics in children with Leigh syndrome - A long-term follow-up

PURPOSE

To describe ophthalmological characteristics in children with Leigh syndrome (LS), an inherited, progressive, mitochondrial encephalomyopathy, at diagnosis and over time, and relate the results to causative genetic mutations.

METHODS

Forty-four children with LS (19 females), with a median age of 2.4 years (range: 0.6-14.2 years) at diagnosis, were studied at the Queen Silvia Children's Hospital, Gothenburg, Sweden. Twenty-eight children had known genetic defects. The children underwent an ophthalmological examination, including visual acuity (VA), eye motility, refraction, slit lamp examination, ophthalmoscopy and a full-field electroretinogram (ff-ERG). Seventeen children were available for follow-up over a mean time of 5.4 years (range: 0.3-14.8 years). The results of these children were compared with an age- and sex-matched reference group of healthy children (n = 119).

RESULTS

Altogether 36/44 of the children (82%) had ophthalmological abnormalities. The most common findings were refractive errors (n = 16/25), low VA (n = 9/36), strabismus (n = 8/42), reduced eye motility (n = 8/40), optic atrophy (n = 7/41), retinal pigmentation (n = 6/40) and nystagmus (n = 6/42). Several ophthalmological manifestations appeared over time. In 5/22 children, ff-ERG showed retinal dystrophy. No significant correlation between phenotype and genotype was found. The children with LS had significantly lower VA (p < 0.0001, Mantel-Haenszel chi-square exact test), more astigmatism (p = 0.012, Fisher's exact test) and higher incidence of strabismus (p = 0.0002) compared to controls at follow-up.

CONCLUSIONS

In this unique cohort of children with LS, the vast majority showed ophthalmological findings at diagnosis, which increased over time. Therefore, we recommend that all children diagnosed with LS should be followed up with regular ophthalmological examinations.

Subretinal deposits, paramacular atrophy and pigmentary retinopathy in mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes

PURPOSE

To report a case of subretinal deposits, paramacular atrophy, and pigmentary retinopathy associated with mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes.

METHODS

Retrospective review of medical records.

RESULTS

A 45-year-old white woman presented with progressive deterioration of vision and dark adaptation over several years. She had a background of an undiagnosed neurodegenerative disorder, including sensorineural hearing loss, cognitive disturbance, and peripheral neuropathy. On examination, subretinal deposits were visible along the superotemporal arcades. A diagnosis of mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes was confirmed by genetic testing (A3243G gene mutation). Four years later, she had developed paramacular atrophy and pigmentary retinopathy.

CONCLUSION

Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes may be associated with paramacular atrophy and pigmentary retinopathy. Autofluorescent changes may precede these signs and can help distinguish this condition from Stargardt disease-fundus flavimaculatus. As far as we are aware, this is the first report of fundus autofluorescence imaging and optical coherence tomography in mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes-associated retinopathy. Subretinal deposit may be an early sign.

The role of SIRT1 in ocular aging

The sirtuins are a highly conserved family of nicotinamide adenine dinucleotide (NAD+)-dependent histone deacetylases that helps regulate the lifespan of diverse organisms. The human genome encodes seven different sirtuins (SIRT1-7), which share a common catalytic core domain but possess distinct N- and C-terminal extensions. Dysfunction of some sirtuins have been associated with age-related diseases, such as cancer, type II diabetes, obesity-associated metabolic diseases, neurodegeneration, and cardiac aging, as well as the response to environmental stress. SIRT1 is one of the targets of resveratrol, a polyphenolic SIRT1 activator that has been shown to increase the lifespan and to protect various organs against aging. A number of animal studies have been conducted to examine the role of sirtuins in ocular aging. Here we review current knowledge about SIRT1 and ocular aging. The available data indicate that SIRT1 is localized in the nucleus and cytoplasm of cells forming all normal ocular structures, including the cornea, lens, iris, ciliary body, and retina. Upregulation of SIRT1 has been shown to have an important protective effect against various ocular diseases, such as cataract, retinal degeneration, optic neuritis, and uveitis, in animal models. These results suggest that SIRT1 may provide protection against diseases related to oxidative stress-induced ocular damage, including cataract, age-related macular degeneration, and optic nerve degeneration in glaucoma patients.

Contribution of muscle biopsy and genetics to the diagnosis of chronic progressive external opthalmoplegia of mitochondrial origin

Chronic progressive external opthalmoplegia (CPEO) is the most common phenotypic syndrome of the mitochondrial myopathies. Muscle biopsy, which provides important morphological clues for the diagnosis of mitochondrial disorders, is normal in approximately 25% of patients with CPEO, thus necessitating molecular genetic analysis for more accurate diagnosis. We aimed to study the utility of various histochemical stains in the diagnosis of CPEO on muscle biopsy and to correlate these results with genetic studies. Between May 2005 and November 2007 all 45 patients diagnosed with CPEO were included in the study (23 males; mean age at presentation, 35 years). Thirty-nine patients had CPEO only and six had CPEO plus; two had a positive family history but the remaining 39 patients had sporadic CPEO. Muscle biopsy samples were stained with hematoxylin and eosin, modified Gomori's trichrome stain, succinic dehydrogenase (SDH), cytochrome C oxidase (COX) and combined COX-SDH. Ragged red fibers were seen in 27 biopsies; seven showed characteristics of neurogenic atrophy only, and 11 were normal. The abnormal fibers were best identified on COX-SDH stain. A complete mitochondrial genome was amplified in muscle and blood samples of all patients. Mutations were found in transfer RNA, ribosomal RNA, ND, CYTB, COX I, II and III genes. Mitochondrial gene mutations were found in ten of the 11 patients with a normal muscle biopsy. The genetic mutations were classified according to their significance. The observed muscle biopsy findings were correlated with genetic mutations noted. Histological studies should be combined with genetic studies for the definitive diagnosis of CPEO syndrome.

[Retinal involvement and genetic myopathy]

INTRODUCTION

In genetic diseases, association between retinal and muscular involvement is uncommon, quite specific and frequently allows the diagnosis. In this context, three types of retinal involvement have been described: retinitis pigmentosa (RP), pattern retinal dystrophy (PRD) and exudative retinitis resembling Coats disease (CD).

STATE OF THE ART

The association between RP, PRD and muscle weakness is highly evocative of a mitochondrial disorder. Extra ocular muscles may be affected, but limb girdle or distal weakness can also be present in association or not with symptoms and signs of multisystemic involvement. In a large number of patients suffering from facioscapulohumeral muscular dystrophy (FSHD), retinal vessels telangectasia can be found at the fundoscopic examination. This finding, which corresponds to a developmental abnormality of peripheral retinal blood vessels, is not progressive and remains clinically asymptomatic. Nevertheless, a few patients with FSHD can develop an exsudative retinopathy resembling Coats disease with the risk of the major complication, recurrent retinal detachments.

PERSPECTIVES AND CONCLUSIONS

Considering the diagnostic interest and the deleterious consequences that may follow retinal involvement, close collaboration between the neurologist and ophthalmologist is needed in order to establish the diagnosis, detect complications early, and set up appropriate therapies.

Concerted action of two novel tRNA mtDNA point mutations in chronic progressive external ophthalmoplegia

CPEO (chronic progressive external ophthalmoplegia) is a common mitochondrial disease phenotype in adults which is due to mtDNA (mitochondrial DNA) point mutations in a subset of patients. Attributing pathogenicity to novel tRNA mtDNA mutations still poses a challenge, particularly when several mtDNA sequence variants are present. In the present study we report a CPEO patient for whom sequencing of the mitochondrial genome revealed three novel tRNA mtDNA mutations: G5835A, del4315A, T1658C in tRNATyr, tRNAIle and tRNAVal genes. In skeletal muscle, the tRNAVal and tRNAIle mutations were homoplasmic, whereas the tRNATyr mutation was heteroplasmic. To address the pathogenic relevance, we performed two types of functional tests: (i) single skeletal muscle fibre analysis comparing G5835A mutation loads and biochemical phenotypes of corresponding fibres, and (ii) Northern-blot analyses of mitochondrial tRNATyr, tRNAIle and tRNAVal. We demonstrated that both the G5835A tRNATyr and del4315A tRNAIle mutation have serious functional consequences. Single-fibre analyses displayed a high threshold of the tRNATyr mutation load for biochemical phenotypic expression at the single-cell level, indicating a rather mild pathogenic effect. In contrast, skeletal muscle tissue showed a severe decrease in respiratory-chain activities, a reduced overall COX (cytochrome c oxidase) staining intensity and abundant COX-negative fibres. Northern-blot analyses showed a dramatic reduction of tRNATyr and tRNAIle levels in muscle, with impaired charging of tRNAIle, whereas tRNAVal levels were only slightly decreased, with amino-acylation unaffected. Our findings suggest that the heteroplasmic tRNATyr and homoplasmic tRNAIle mutation act together, resulting in a concerted effect on the biochemical and histological phenotype. Thus homoplasmic mutations may influence the functional consequences of pathogenic heteroplasmic mtDNA mutations.

A novel deletion in the GTPase domain of OPA1 causes defects in mitochondrial morphology and distribution, but not in function

Autosomal dominant optic atrophy (ADOA), the commonest cause of inherited optic atrophy, is caused by mutations in the ubiquitously expressed gene optic atrophy 1 (OPA1), involved in fusion and biogenesis of the inner membrane of mitochondria. Bioenergetic failure, mitochondrial network abnormalities and increased apoptosis have all been proposed as possible causal factors. However, their relative contribution to pathogenesis as well as the prominent susceptibility of the retinal ganglion cell (RGC) in this disease remains uncertain. Here we identify a novel deletion of OPA1 gene in the GTPase domain in three patients affected by ADOA. Muscle biopsy of the patients showed neurogenic atrophy and abnormal morphology and distribution of mitochondria. Confocal microscopy revealed increased mitochondrial fragmentation in fibroblasts as well as in myotubes, where mitochondria were also unevenly distributed, with clustered organelles alternating with areas where mitochondria were sparse. These abnormalities were not associated with altered bioenergetics or increased susceptibility to pro-apoptotic stimuli. Therefore, changes in mitochondrial shape and distribution can be independent of other reported effects of OPA1 mutations, and therefore may be the primary cause of the disease. The arrangement of mitochondria in RGCs, which degenerate in ADOA, may be exquisitely sensitive to disturbance, and this may lead to bioenergetic crisis and/or induction of apoptosis. Our results highlight the importance of mitochondrial dynamics in the disease per se, and point to the loss of the fine positioning of mitochondria in the axons of RGCs as a possible explanation for their predominant degeneration in ADOA.

Spinocerebellar ataxia type 7 mimicking Kearns–Sayre syndrome: A clinical diagnosis is desirable

Spinocerebellar ataxias are a group of autosomal dominant cerebellar degenerative disorders, which are characterized by clinical and genetic variability. Spinocerebellar ataxia type 7 (SCA7) is less variable in clinical presentation than other SCAs. We present a pediatric patient with 13 and 70 trinucleotide CAG repeats within SCA7 gene and no family history, whose presentation mimicked Kearns-Sayre syndrome (KSS). We review the differential diagnosis of cerebellar ataxia with vision loss secondary to retinal pigmentary dystrophy. This paper supports concept of a desirable clinical diagnosis to avoid multiple genetic or invasive testing in children with neurodegenerative disorders.

Electron microscopic findings in levator muscle biopsies of patients with isolated congenital or acquired ptosis

OBJECTIVE

Systemic mitochondriopathies as chronic progressive external ophthalmoplegia (CPEO) are frequently associated with ptosis. We investigated whether mitochondrial abnormalities in the levator muscle are also found in patients with isolated congenital or acquired ptosis showing no other signs of mitochondrial cytopathy.

METHODS

Biopsies of levator muscle were taken during surgery from 24 patients with isolated congenital (group 1) or early-onset acquired ptosis (group 2). All patients were given a thorough clinical examination before and after surgery. Ultrathin muscle sections were examined by transmission electron microscopy. The findings were compared with biopsies from five patients with CPEO (positive control) and two patients with traumatic ptosis or pseudoptosis (negative control).

RESULTS

The mean levator function equalled 7.3 mm (range 4-10 mm) in group 1 and 12.8 mm (range 9-15 mm) in group 2. Eight out of 11 patients in group 1 and eight out of 13 patients in group 2 were found to have mitochondrial alterations such as megamitochondria, mitochondrial matrix alterations and abnormal cristae, similar to CPEO. Within group 1 and 2, no significant clinical differences were found between patients with and without mitochondrial abnormalities.

CONCLUSION

Mitochondrial alterations were found in a surprisingly large proportion of levator biopsies from patients with isolated congenital or early-onset acquired ptosis. There was no statistically significant correlation between mitochondrial alterations and levator function. Our findings suggest that the ultrastructural assessment of mitochondria in the eyelid muscle is a valuable tool, and may guide further biochemical and mutation screening tests that will help to understand the etiopathology of this disease.

Early-onset ophthalmoplegia in Leigh-like syndrome due to NDUFV1 mutations

Mitochondrial disorders can be linked to mutations in both mitochondrial and nuclear deoxyribonucleic acid, corresponding to various clinical phenotypes. Mutations in nuclear genes, including NDUFV1, have been associated with severe encephalomyopathies in infants, but genotype-phenotype correlations have remained elusive. This report details the complete clinical, biochemical, and molecular data of a 7-year-old male who presented at the age of 7 months with progressive ophthalmoplegia and later developed cerebellar ataxia, spasticity, and dystonia. Complex I deficiency was demonstrated in muscle, and two pathogenic missense mutations were present in the NDUFV1 gene. Ketogenic diet has seemingly improved the oculomotor palsy but has been unable to correct other neurologic symptoms. Considering other cases from the literature, this report broadens our understanding of genotype-phenotype correlations for NDUFV1 mutations and illustrates a potential and partial efficacy of ketogenic diet in complex I deficient patients.

Orbital magnetic resonance imaging of extraocular muscles in chronic progressive external ophthalmoplegia: specific diagnostic findings

INTRODUCTION

Chronic progressive external ophthalmoplegia (CPEO) is characterized by slowly progressive bilateral ophthalmoplegia and blepharoptosis. Molecular diagnosis is problematic because sporadic mitochondrial DNA deletions can be causative. We sought findings using magnetic resonance imaging (MRI) that might support the diagnosis of CPEO.

METHODS

Two men (ages 31 and 47 years) and 3 women (ages 40-49 years) with CPEO and symptom durations of 8 months to 28 years underwent high-resolution (2-mm slice thickness, 312 micron pixels), surface coil, T1-weighted orbital MRI in coronal planes. Images were analyzed quantitatively to determine extraocular muscle (EOM) sizes and were compared with 10 age- and gender-matched normal volunteers, one subject with myasthenia gravis, and with 30 subjects having EOM paralysis caused by oculomotor, trochlear,0 and abducens neuropathies.

RESULTS

EOM function was clinically diminished in CPEO, most markedly for the superior rectus (SR) and levator muscles. All EOMs in CPEO exhibited unusual qualitative T1 MRI signal abnormalities. Unlike the profound EOM atrophy typical of neurogenic paralysis, anterior volumes of medial rectus, lateral rectus, and inferior rectus muscles in CPEO were not smaller than normal (p>0.003). Anterior volumes of the SR muscle-levator complex and superior oblique were significantly reduced (p<0.003). Denervated EOMs exhibited statistically significant volume reduction when compared with normal and CPEO groups. Volume of the SR muscle-levator complex was the same in subjects with CPEO and oculomotor palsies.

CONCLUSIONS

CPEO is associated with minimal EOM volume reduction despite clinically severe weakness. This combination of findings may be specific for CPEO and could resolve the diagnostic dilemma in difficult cases.

Hereditary optic neuropathies: from the mitochondria to the optic nerve

PURPOSE

To review our current knowledge of inherited optic neuropathies.

DESIGN

Perspective.

METHODS

Literature review.

RESULTS

The hereditary optic neuropathies consist of a group of disorders in which optic nerve dysfunction figures solely or prominently and direct inheritance is clinically or genetically proven. The most common of these disorders are autosomal dominant optic atrophy (Kjers' disease) and maternally-inherited Leber's hereditary optic neuropathy. Other inherited neurologic and systemic syndromic diseases will frequently manifest optic neuropathy. A selective vulnerability of the optic nerve to perturbations in mitochondrial function may underlie a final common pathway among these disorders.

CONCLUSIONS

The ophthalmologist should be familiar with the clinical characteristics and diagnosis of the hereditary optic neuropathies. Recent advances in our understanding of the underlying pathophysiology of the inherited optic neuropathies may provide insight into their treatment and the treatment of acquired optic nerve disorders.

Hereditary optic neuropathies

AIMS

To provide a clinical update on the hereditary optic neuropathies.

METHODS

Review of the literature.

RESULTS

The hereditary optic neuropathies comprise a group of disorders in which the cause of optic nerve dysfunction appears to be hereditable, based on familial expression or genetic analysis. In some hereditary optic neuropathies, optic nerve dysfunction is typically the only manifestation of the disease. In others, various neurologic and systemic abnormalities are regularly observed.

CONCLUSION

The most common hereditary optic neuropathies are autosomal dominant optic atrophy (Kjer's disease) and maternally inherited Leber's hereditary optic neuropathy. We review the clinical phenotypes of these and other inherited disorders with optic nerve involvement.

The role of the ND5 gene in LHON: Characterization of a new, heteroplasmic LHON mutation

Leber's hereditary optic neuropathy (LHON) causes central vision loss from bilateral optic neuropathy. Although 13 mitochondrial DNA (mtDNA) mutations are strongly associated with LHON, only three account for roughly 90% of cases and thus are found in multiple independent LHON families. The remaining LHON mutations are rare. Here, we describe the clinical and genetic characterization of a new LHON mtDNA mutation. The 12848T mutation alters a highly conserved amino acid in the ND5 complex I gene, is not found in controls, and is heteroplasmic. Despite ND5 being the largest of the mtDNA complex I genes, ND5 mutations are quite rare in LHON.

Diagnostic value of mitochondrial DNA mutation analysis in juvenile unilateral ptosis

PURPOSE

To highlight the diagnostic relevance of mitochondrial DNA (mtDNA) mutation analysis in acquired juvenile unilateral upper eyelid ptosis.

METHODS

A 13-year-old boy presented with acquired, slowly progressive unilateral ptosis. We performed ophthalmological and neurological examinations, laboratory testing, skeletal muscle biopsy including histological and histochemical investigations, biochemical analysis of respiratory chain enzymes in skeletal muscle homogenate and molecular genetic testing of skeletal muscle DNA.

RESULTS

Though clinical, laboratory, histological and biochemical analyses did not reveal any hints suggesting a mitochondrial cytopathy, molecular genetic testing by Southern blot analysis of total DNA from skeletal muscle tissue showed a 5.8 kb mtDNA deletion thus proving the diagnosis of mitochondrial chronic progressive external ophthalmoplegia (CPEO).

CONCLUSIONS

In patients with unexplained acquired juvenile unilateral ptosis, an underlying mitochondrial cytopathy should be considered even in cases of inconspicuous ancillary examinations comprising skeletal muscle histology and biochemistry. To establish the diagnosis, molecular genetic testing of DNA derived from skeletal muscle tissue is essential in those patients.

Toxic optic neuropathy

Toxic optic neuropathy is a complex, multifactorial disease potentially affecting individuals of all ages, races, places, and economic strata. Etiology includes nutritional, environmental, toxicologic, and genetic factors. Most cases of nutritional amblyopia are encountered in disadvantaged countries. However, toxic amblyopia related to drug treatment or alcohol abuse is also encountered in the Western world. Typically, toxic and nutritional optic neuropathy is progressive, with bilateral symmetrical painless visual loss causing central or cecocentral scotoma. There is no specific treatment for this disorder. Nevertheless, early detection and prompt management may ameliorate and even prevent severe visual deficit.