Résumé :
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Communication n° 528 Background : Autosomal recessive ataxias represent a large group of neurodegenerative disorders characterized by progressive degeneration of the central and the peripheral nervous systems. Objective : To report clinical, neurophysiological and nerve biopsy findings of 14 Tunisian unrelated families showing linkage exclusion with the known autosomal recessive ataxia loci. Methods : 14 Tunisian families with a total of 35 affected were selected on the presence of a clinical phenotype associating cerebellar ataxia with retained tendon reflexes on at least the index patient and genetic linkage showing exclusion with FRDA, AVED and ARSACS loci. Genetic linkage study was performed with markers spanning the two AOA (9p13 and 9q43), the ISOCA (10p23), the HLOA (6p21), the FRDA2 (9p23), the AT (11q22), ATLD (11q21), SCAN1 (14q31), ATCAY (19p13), CAMOS (9q34), Salla syndrome (6q14) and Marinesco-Sjögren (5q31) loci. Two point linkage analysis was preformed using the LINKAGE program. Results : Patients were divided in three groups according to tendon reflexes status in lower limbs which appear as the most obvious distinguishing clinical sign between patients and families: Group A, characterized by a homogeneous feature of tendon reflexes with the absence of ankle reflexes and brisk knee reflexes. Group B, characterized by brisk tendon reflexes in lower limbs. Group C, characterized by variable features of tendon reflexes in lower limbs within the same family. Haplotype analysis and Lod score calculation did not show any evidence of linkage to the 12 known loci of cerebellar ataxias. Conclusion : Due to the clinical variability, we classified all the families studied on three phenotypic groups. This may help in the mapping of the responsible gene in more homogenous groups with more informative families segregating these neurological phenotypes.
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