Decreased cerebrovascular reserve capacity in patients with various types of mitochondrial disorders

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Abstracts

tion at codon 12). Both patients were homozygous for this mutation and the asymptomatic parents of patient 1 were heterozygous carriers. Our data suggest that AMPD deficiency can cause episodes of severe myalgia in childhood, apparently triggered by fever. (C.B. is supported by TelethonItaly)

GP3.11 Threshold expression of the tRNA ly~ A8344G mutation in single muscle fibres A.-R. Moslemi a, M. Tuliniusb, E. Holme ~, A. Oldfors~

aDepartment of Pathology, °Paediatrics and CClinical Chemistry, Sahlgrenska Universio, Hospital, GOteborg, Sweden

Keywords: AMP deaminase; Metabolic myopathy; Molecular diagnosis

GP3.9 Abnormal muscle energy metabolism in chronic fatigue syndrome patients: evidence from muscle histometry, spectroscopy and in vitro mitochondrial function studies Russell J.M. Lane a, Michael C. Barrett ~, Doris M. Taylorb, John Cooper~, Anthony H. Schalbira~

"Charing Cross and Westminster Medical School, eRoyal Free Hospital Medical School London, bMRC Magnetic Resonance Unit, John Radcliffe Hospital, Oxford, UK Some patients fulfilling operative criteria for a diagnosis of chronic fatigue syndrome (CFS) show an abnormal increase in plasma lactate following a short period of moderate exercise, in the sub-anaerobic threshold exercise test (SATET). Histometric analysis of muscle from 105 cases did not show changes expected as a result of 'disuse', but SATET + ve patients had significantly fewer Type 1 muscle fibres than SATET-ve cases (P < 0.01). Phosphorus MRS studies of forearm muscles comparing 10 of the SATET + ve with 9 of the SATET-ve cases, and with 13 sedentary normal volunteers, showed that CFS cases generally showed more rapid intracellular acidification during exercise, but the SATET + ve patients failed to compensate for this because of impaired mitochondrial oxidative phosphorylation capacity. In vitro studies in 3 SATET + ve cases demonstated reduced Complex I function.

GP3.10 Cytochrome c oxidase deficiency linked to a new stop codon point mutation in mitochondrial DNA M.G. Hanna, I.P. Nelson, S. Rahman, A.H.V. Schapira, J.M. Cooper, J.A. Morgan-Hughes, N.W. Wood

Neurogenetic and Muscle disease sections, Institute of Neurology, Queen Square, London WClN 3BG, UK Although cytochrome c oxidase (COX) deficiency is recognised to present from the neonatal period to adult life, in the majority of cases its molecular genetic basis has not been defined. We have identified a 36 year old woman with recurrent encephalopathy associated with lactic acidosis, proximal myopathy and exercise induced myalgia. Muscle histochemistry showed that 90% of the fibres exhibited very low or absent COX activity and there were no ragged red fibres. Enzymatic studies identified an 80% reduction of COX activity and cytochrome studies revealed a marked reduction in cytochrome aa3 at 23% of normal. Immunocytochemistry with antibodies to both mitochondrial and nuclear encoded subunits revealed a pattern suggestive of a primary mitochondrial DNA (mtDNA) defect in the COX deficient fibres and consistent with either reduced stability or impaired assembly of the holoenzyme. Sequence analysis of mtDNA identified a heteroplasmic G to A point mutation at position 9952 in skeletal muscle which was not detectable in leukocyte mtDNA and not identified in 120 healthy controls or 50 patients with other mitochondrial encephalomyopathies. Mass myoblast and fibroblast cultures did not harbour the mutation. This mutation creates a premature stop codon in the highly conserved C terminal region of the COX III subunit which predicts the loss of the last 12 amino acids. Single fibre polymerase chain reaction studies provided further evidence for an association between this mutation and COX deficiency. This is the first stop codon mutation identified in human mitochondrial DNA.

Keywords: Cytochrome c oxidase; Mitochondrial DNA; Point mutation

We investigated the distribution in skeletal muscle of mitochondrial DNA (mtDNA) with the tRNAlys A8344G mutation, which is associated with myoclonus epilepsy and ragged red fibres (MERRF). Isolated muscle fibre segments (n = 144) from 6 individuals of two different families carrying the mutation were studied. Two of these individuals were affected by MERRF while four had no or less severe clinical symptoms. In one individual with low overall level of mutated mtDNA (mean 18%) there was a marked variation in the proportion of mutated mtDNA between individual muscle fibres (range 0-80%). This result demonstrate that segregation of the tRNAlys A8344G mutation within a tissue occurs, and may lead to very marked variation of the level of mutated mtDNA between individual cells. In the other patients, who all had high levels of mutated mtDNA (86-98%) the variability between individual muscle fibres was less pronounced. A very high threshold level of mutated mtDNA (9597%) for expression of histochemical cytochrome c oxidase (COX) deficiency was found in the four patients with COX deficient muscle fibres. All fibres with more than 96% mutated mtDNA were COX deficient in two individuals, whereas up to 98% of mutated mtDNA was found in fibres with normal appearance in two patients. The results indicate a difference in relative threshold level in different patients for expression of disease at the biochemical level, Which also might be a basis for variation in clinical phenotype of patients with high levels of the tRNAlys A8344G mutation. GP3.12 Mitochondrial dysfunction with MERRF point-mutation in nerve and muscle tissue of a patient with multiple symmetric lipomatosis H. Reichmann a, M. Naumannb, R. Kiefer~, P. Seibel b, K. Toyka b

"Department of Neurology, University of Dresden, Germany, bDepartment of Neurology, UniversiO, of Wurzburg, Germany We report a 64-year old man presenting with multiple symmetric lipomatosis and mitochondrial encephalo-myo-neuropathy. The diagnosis of a mitochondrial cytopathy was based on the typical clinical symptoms and signs including chronic progressive external ophthalmoplegia, hearing impairment, cerebellar ataxia, proximal myopathy, and polyneuropathy, and on molecular genetic and histological examinations. As a unique finding, the A-G ~8344~ MERRF point mutation was found in peripheral nerve and muscle tissue. Muscle biopsy revealed multiple ragged-red fibres and other morphological signs of a mitochondrial myopathy. Sural nerve biopsy demonstrated a mixed axonal and demyelinating neuropathy with conspicuous onion bulb formations. These findings clearly demonstrate mitochondrial dysfunction in muscle and for the first time also in nervous tissue and support strongly the concept of mitochondrial cytopathy as one of the possible causes of multiple symmetric fipomatosis. Finally, we were able to detect the point mutation in lipomas.

GP3.13 Decreased cerebrovascular reserve capacity in patients with various types of mitochondrial disorders M. Molnar, A. Valikovics, P. Di6szeghy, D. Bereczki, F. Mechler, L. Csiba

Department of Neurology, University of Debrecen Medical School, Hunga©' Background and purpose. Previous studies on patients with mitochondriopathies revealed accumulations ot mitochondria in endothelial cells, smooth muscle cells of cerebral and cerebellar blood vessels, in pericytes of capillaries, endothelial cells, and smooth muscle cells of small blood vessels in skeletal muscle and in sural nerves (Ohama et al., Acta Neuropathol 1987:74:226-233; Fujii et al., J Neurol Sci 1991;103:37-41; Mol-

Abstracts" nar et al., Neuropathol Appl Neurobiol 1995;21:432-439; Kodaka et al., Stroke 1996;27:1350-1353). To elucidate the pathogenic role of vascular involvement in patients with mitochondriopathy, we used the transcranial Doppler sonography (TCD) method to detect the impairment of acetazolamide reactivity. Based on CO2 reactivity measurements by TCD, Kodaka et al. suggested the decreased cerebrovascnlar reserve capacity in mitochondrial encephalomyopathies (Kodaka et al.). Patients and methods. The cerebrovascular reserve capacity in 13 patients with mitochondrial myopathy and encephalopathy was studied by TCD. The patients were divided into three groups: (i) patients with mitochondrial encephalomyopathy, lactacidosis and stroke like episodes (MELAS), (ii) patients with symptoms of progressive external ophthalmoplegia (PEn), (iii) patients with pure mitochondrial myopathy and neuropathy. The diagnoses were based on clinical, histopathological, and on molecular biological investigations. Results. The cerebrovascular reserve capacity of the patients with mitochondriopathy was decreased, but not significantly, compared to that of the healthy control group. There were no significant differences between the patients with stroke-like episodes and without central nervous system involvement. Conclusion. Our results suggest that there is a high incidence of impairment of cerehrovascular acetazolamide reactivity in mitochondriopathies. The clinical symptoms are not the direct consequence of mitochondrial angiopathy, but the results of a systemic mitochondrial cytopathy, which involves the blood vessels as well. This hypothesis supports the increase of mitochondria in vasa nervomm of cases with mitochondrial myopathy, Keams-Sayre syndrome, progressive external ophthatmoplegia and MELAS as well (Molnar et al.).

Keywords: Mitochondriopathy; Transcranial Doppler; Acetazolamide GP3.14 Peripheral neuropathy associated with mitochondrial myopathy Chun-Che Chu a, Chin-Chang Huanga, Yau-Huei Wei b

~Department of Neurology, Chang Gung Memorial Hospital and Medical College and bDepartment of Biochemistry and Center for Cellular and Molecular Biology, National Yang-Ming University, Taipei, Taiwan Seven patients with mitochondrial myopathy were studied for peripheral neuropathy by clinical, electrophysiological and pathological examinations. The clinical manifestation of neuropathy varied from asymptomatic to mild and moderate sensorimotor symptoms. Five patients (two with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes, and three with myoclonic epilepsy and ragged-red fibres) had clinical symptoms and signs of polyneuropathy associated mainly with decreased amplitudes of the compound muscle or nerve action potentials in an electrophysiological study indicating axonal degeneration. Sural nerve biopsy from 1 MERRF and 1 MELAS patient, also confirmed an axonal degeneration with decreased fibre density, reduction of large myelinated fibres and paracrystalline inclusion bodies. Mitochondrial DNA analysis of the sural nerve from the MERRF patient showed a point mutation from A to G transition at the nucleotide position 8344 with 80% mtDNA mutation. However, an A3243G point mutation of mtDNA was found in the blood cells and muscles, but not in the sural nerve specimen in the MELAS patient. The data indicated that mtDNA mutation analysis is not absolutely reliable in the diagnosis of the involvement of specific tissues in patient with some mitochondrial diseases. The results of this study suggest that peripheral neuropathy is not uncommon in mitochondrial myopathies and is predominantly due to axonal degeneration.

Keywords: Mitochondrial myopathy; Peripheral neuropathy; Sural nerve biopsy GP3.15 Mitochondrial myopathy with demyelination polyneuropathy N. Gonider-Khouja, M. Dabbeche, I. Turki, S. Oueslati, N. Miladi, M. Ben Hamida, F. Hentafi

lnstitut National de Neurologie, la Rabta 1007, Tunis, Tunisia

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The association of mitochondrial myopathy with peripheral neuropathy, mostly as a subclinical finding and of axonal mechanism, is a known eventuality. The occurrence of this association in infancy with the neuropathy presenting as a demyelinating polyradiculoneuropathy is rare. We report 3 cases, one boy (4 years and 5 months) and 2 girls (2 years and 1 year 2 months). Two patients had a clinical picture of delayed motor skills, generalised muscular weakness involving ocular muscles, hypotonia and absent tendon reflexes and the third had relapsing episodes of tetrapleglia with absent tension reflexes. CSF analysis showed a very high level of proteins in all patients (5.20-10.80 g/l) without pleiocytosis in 2 and with a mild transient increased cellularity in CSF in the third. Improvement in motor function was observed spontaneously in one child, under steroid treatment in one other. Relapsing course was observed in the third. Electromyography and nerve conduction study showed mixed axonal and myelinic mechanism. Clinical course was CIDP in 2 cases and relapsing CIDP. Muscle biopsy showed ragged red fibers in the three cases, associated with lipidic changes in one case and lipid and glycogenic muscle storage in the third. GP3.16 Thymomagenic myasthenia and demyelinization - immunodepended continuum Roman R. Shakarishvili, Nana B. Kvirkvelia. Dali M. Kankava

Sarajishvili Institute of Neurology 2a Gudamakari, Tbilisi. Georgia Four cases are presented that illustrate the occurrence of thymomagenic myasthenia and demyelinization processes in the same patient. The exact mechanism responsible for the association of these autoimmune diseases is unknown. The key autoantigens of myasthenia gravis (MG) and multiple sclerosis (MS) are cnexpressed in thymus. Both MS and MG are accompanied by hyperplasia of thymus. Therefore, these diseases can be initiated in thymus. Possibly, thymustropic pathogens such as viruses may provide the initial stimulus through inducing initial tissue damage in thymus. Effective presentation and co-stimulation by infected antigen-presenting cells can occur in thymic medulla, leading to activation of the previously quiescent autoreactive T-cells specific to myelin basis protein (MBP) and acetylcholine receptor. Activation of specific autoreactive T-cells is the key event in subsequent development of MS and MG. Expansion of autoimmune induced inflammation in thymus would affect the process of T-cell development and differentiation. Inappropriate expression of developmental and differential antigens on thymocytes can lead in genetically predisposed individuals to generation of thymomas. Another scenario for the association of these diseases can be: the primary activation of myelin reactive T-cells by microbes of superantigen can take place in the periphery. Activated T-cells have preterenfial entry into the thymic medulla. Myelin-reactive activated T-cells may cause T-cell mediated inflammation processes directed against MBP epitope not only in the brain but also in the thymus. Thus single MBP epitope would give rise to the first attack of the target organ, that would result in T-cell mediated inflammation and development of multiple autoimmune reactions due to spread sensitisation. This mechanism would enhance autoantigen presentation or release of immunogenic cell components, that would give rise to a secondary autoimmune response, possibly to acetylcholine receptor.

Keywords: Myasthenia; Myelinopathy; Thymus GP3.17 Oral muscle functions in patients with myasthenia gravis F.G. Weijnen, A. van der Bilt, H.W. van der Glas, F. Bosman, J.H.J. Wokke

Department of Oral Pathophysiology, Universiteit Utrecht, Utrecht, The Netherlands Myasthenia gravis (MG) is an autoimmune disease mediated by antibodies directed against acetylcholine receptors. MG patients with bulbar involvement may suffer from difficulties in swallowing and chewing,