Friedreich's ataxia phenotype with vitamin E deficiency (FAVED): an overview

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Abstracts

NAI5 The frataxin story Victoria Campuzano~, Hana Koutnikovaa, Fran~oise Fouryb, Mireille Coss6e~, Ornella Cazzalini b, Michel Koenig"

~Tnstitut de Gdndtique et Biologie Moldculaire et Cellulaire (IGBMC), lllkirch -Strasbourg, France, bUnitd de Biochimie Physiologique, Universitd Catholique de Louvain, Louvain-la Neuve, Belgium Friedreich ataxia is caused by loss of function of frataxin, a novel protein conserved through evolution down to yeast. We cloned the entire mouse frataxin coding sequence that is very homologous to the human sequence except over the first two exons. The N-terminal sequence of yeast and mouse frataxin is compatible with a mitochondrial target sequence while the human sequence fit less well the consensus. On northern blot of mouse tissues, the cDNA probe revealed a single transcript of 1.2 kb in agreement with the major transcript seen in humans. The mouse clone was used to determine the expression pattern in adult and embryonic tissues by in-situ hybridization. The frataxin gene is expressed in selected parts of the nervous system (the dorsal root ganglia, the granular layer of the cerebellum and the ependymal layer of the periventricular zone of brain) but also in liver, heart, brown fat, kidney and other tissues which are known to be rich in mitochondria. We developed specific monoclonal antibodies against human frataxin, in order to determine its subcellular localisation. Mapping of the N terminal and C terminal antibodies indicated that the full length frataxin (30 kDa) is matured into a 17-20 kDa protein by cleavage of the N-terminal sequence No evidence of a larger protein product was found in various tissues. The antibodies were used to localise by immunofluorescence frataxin in the mitochondria. Additional support for mitochondrial localisation was obtained with subcellular fractionation by differential centrifugation and by frataxin tagging, the latter being independent of antibody specificity. Frataxin was further sublocalized to mitochondrial membranes by immuno-electron microscopy. The yeast knock-out share properties with known mitocfiondrial deficient mutants. In particular, when grown on glycerol, clones either fail to grow or accumulate mitochondrial DNA deletion. Respiration was also found to be less than 10% of the wild type. Strikingly, the yeast mutant accumulates 10 fold more iron in the mitochondria than the wild type, the total iron content being otherwise normal. The subcellular localisation of frataxin and the phenotype of the corresponding yeast deletant indicate a mitochondrial function that may result in oxidative stress and shed new light on similar clinical entities such ataxia with isolated vitamin E deficiency (AVED) and possibly also with mitochondrial diseases such as MERRF and NARP.

NAI6 Friedreich's ataxia phenotype with vitamin E deficiency (FAVED): an overview Fay~al Hentati

lnstitut National de Neurologie, Tunis, Tunisia FAVED is an autosomal recessive neuro-degenerative disease, characterised clinically by a stereotyped clinical feature, and defined by selective vitamin E (vit. E) deficiency. The defective gene of FAVED has been mapped on chromosome 8 and identified as the alpha tocopherol transfer protein (alpha TTP) gene. FAVED is frequently encountered in Tunisia and all Tunisian patients show the same del 744 mutation in the alpha TTP gene. However, various other mutations responsible for milder clinical phenotypes of ataxias (AVED) have been reported. FAVED has similar clinical features, including, age of onset of inability to walk and death, like FA. The frequency of cardiomyopathic changes were similar. However in FAVED there is more frequently pseudo-bulbar syndrome, head tremulation, choreo-athetosis, pigmentary" retinitis and optic atrophy. Diabetes mellitus is infrequent in FAVED. Neurophysiological studies, in FAVED, showed normal to mild reduction of motor nerve conduction velocity (MNCV), normal to moderate reduction of sensory action potential with normal sensory nerve conduction velocity. Sensory evoked potentials were severely affected suggesting posterior tracts involvement. Nerve

biopsy showed a mild and late occurring peripheral sensory axonal neuropathy. The main neuropathologicat findings in FAVED are posterior column demyelination with neuronal atrophy and axonal spheroids, neuronal storage with granular lipopigment accumulation. The neurodegenerative process in FAVED seems to be related to the oxidative stress, caused by an accumulation of free radicals, suggesting that pathogenic mechanisms involved in these two phenotypically similar disorders FAVED and FA are distinct.

NEUROPATHIES AND ATAXIAS: ORAL PRESENTATION NAO1 Clinical, electrophysiological and neuropathological findings in an autosomal dominant CMTIC family P. De Jonghea'b, E. Nelis a, A. Lofgren~, E. De Vriendt a, V. Timmermana, C. Ceuterick c, J.-J. Martin bx, C. Van Broeckhovena

~Laboratoo' of Neurogenetics, Flanders lnteruniversi~, Institute for Biotechnology (VIB), Born-Bunge Foundation (BBS), Universit3, of Antwerp ( UIA), Department of Biochemistry, Antwerp, Belgium, t'Division of Neurology, University Hospital (UZA), Antwerp, Belgium, "Laboratory for Neuropathology, Born-Bunge Foundation (BBS), University of Antwerp (U1A), Department of Medicine, Antwerp, Belgium The proband of family CMT-54 was well until the age of 41 years when a diagnosis of thromboangiitis obliterans was made. Clinical neurological examination demonstrated bilateral pes cavus, slight weakness of the peroneal muscles and distal areflexia in the lower limbs. A follow up examination 13 years later showed diminished sensation below the knees. The father of the patient and 3 sibs of the proband were asymptomatic but clinical examination demonstrated pes cavus and in some individuals slight problems in walking on the heels. Motor and sensory nerve conduction velocities were slowed to less than 43 m/s for the motor median nerve (range of our CMTIA patients with the 1.5 Mb duplication in chr. 17pl 1.2: motor median nerve <43 m/s). A biopsy of the superficial fibular nerve showed a loss of myelinated axons, thin myelin sheaths and a few onion bulbs. Sequencing of the coding region of the MPZ and PMP-22 gene did not reveal any abnormality. Genetic linkage studies excluded linkage to the CMTIA locus at chr. 17pl 1.2 and the CMTIB locus at chr. Iq22-q23. A genome-wide search will be performed to map the gene in this CMT1C family.

Keywords: Inherited peripheral neuropathies; Charcot-Marie-Tooth disease type IC

NAO2 Homozygosity mapping of an autosomal recessive form of demyelinaling Charcot-Marie-Tooth disease to chromosome 5q23-q33 E. LeGuern a'b, A. Guilbot a, M. Kessali d, N. Ravise ~, J. Tassina, T. Maisonobec, D. Grid d, A. Brice a'"

alNSERM U289, bFederation de Neurologie, ':Laboratoire de Neuropathologic R. Escourolle, H~pital de la Salpgtribre, Paris, France, dService de Neurologie, CHU Mustapha, Alger, Algeria Charcot-Marie-Tooth (CMT) disease is the most frequent inherited peripheral motor and sensory neuropathy characterised by chronic distal weakness with progressive muscular atrophy and sensory loss of the distal extremities. The recessive form of the disease is genetically heterogeneous because three loci have been identified on chromosome 8q13-q21.1, 1 lq23.1 and 8@4. By homozygosity mapping in a large Algerian kindred, we have assigned a third locus for autosomal recessive CMT to chromosome 5q23-q33. Linkage analysis demonstrated that the same locus is involved in a second Algerian family with a demyelinating CMT. Haplotype reconstruction and determination of the minimal region of homozygosity restricted the candidate region to a 4 cM interval. We performed a physical map of the 5q31-q33 region from a YACs contig already published. Molecular analysis demonstrated that this contig overlapped the homozygosity region and nine microsatellites of the Genethon map were