INTRODUCTION Deafness is the most frequent nonsyndromic sensori- neural defect in humans. It is estimated that 75% of in- herited nonsyndromic deafness is caused by autosomal recessive defects 1 . Classical studies have demonstrated genetic heterogeneity for nonsyndromic autosomal re- cessive congenital neurosensory deafness (NSRD) 2 . Up to now, 14 loci have been mapped (DFNB1- DFNB12, DFNB15, DFNB16) [http://dnalab- www.uia.ac.be/dnalab]. However, DFNB8 and DFNB10, DFNB7, and DFNB11 have been assigned to the same chromosomal regions. The DFNB1 and DFNB2 locations were found in two consanguineous Tunisian families 3,4 . Mutations in the connexion 26 gene have been shown to be responsible for DFNB1 5 . A deletion of a G at position 30 (30 del G) of the coding exon is present in 63% of the DFNB1 allele 5,8 . The first DFNB2 mutation was identified as a G to A transition at the last nucleotide of exon 15 in the Myosin VIIA gene 9 . By screening families with non-syndromic deafness from China Liu and al 10 have identified three other mutations. In order to determine the contribution of these loci in the NSRD pathology in southern Tunisia, 24 unrelated families were studied with microsatellite markers corresponding to the DFNB1 and DFNB2 loca- tions 3,4 . None of these families was linked to DFNB2, whereas, three of them cosegregated with DFNB1. SUBJECTS AND METHODS SUBJECTS Twenty three Families were ascertained through files at the “Association d’Aide aux Sourds et Muets Section de Sfax” in 1995 11 and further one (family TOU) was re- cruited later in 1996. Each of them included at least two offsprings with NSRD and that had a pedigree consis- tent with autosomal recessive inheritance. Thirty nine affected subjects were submitted to clinical, otoscopic and audiometric examination in the department of oto- rhinolaryngology. In these affected children, no asso- ciated symptomps such as external ear abnormality, mental retardation, renal or eye disorder were noted. Archs. Inst. Pasteur Tunis , 1997, 74 ( 1 /2 ) 5 CONTRIBUTION OF DFNB 1 AND DFNB2 LOCI TO NEUROSENSORY DEAFNESS IN AFFECTED TUNISIAN FAMILIES A. BOULILA-ELGAÏED 1 , S. MASMOUDI 1 , M. DRIRA 3 , M. GOUIA 3 , H. CHAIB 2 , Ch. PETIT 2 , H. AYADI 1 1 Laboratoire d’Immunologie et de Biologie Moléculaire Faculté de Médicine, 3028 Sfa x, TUNISIE 2 Unité de Génétique Moléculaire Humaine, Institut Pasteur, 25 rue du Dr Roux, Paris 15e, FRANCE 3 Service d’O.R.L C.H.U H. Bourguiba, 3028 sfax, TUNISIE ABSTRACT Classical studies have demonstrated genetic heteroge- neity for nonsyndromic autosomal recessive congenital neurosensory deafness. The first two DFNB1 and DFNB2 locations were found using two consanguineous Tunisian families respectively from north and south. We tested these loci for cosegre- gation with deafness in twenty four southern families with nonsyndromic presumed congenital sensorineu- ral deafness and a pedigree structure consistent with autosomal recessive inheritance. Only in our families, did deafness cosegregate with DFNB1. Although our families are from the south, none of them showed linkage to DFNB2 Keywords: Neurosensory deafness, DFNB1, DFNB2, Microsatellite markers. RESUME Des études de génétiques classiques ont montré que la surdité autosomique récessive est très hé- térogène. Récemment, par l’approche de géné- tique inverse, deux loci DFNB1 et DFNB2 ont été déterminés en utilisant deux familles tunisiennes consanguines originaires respectivement du nord et du sud tunisien. Nous avons testé ces deux loci à la recherche d’une coségrégation avec la surdité dans 24 familles issues du Sud tu- nisien. Ainsi nous avons trouvé que 3 familles coségrègent avec DFNB1 alors qu’aucune liaison avec DFNB2 n’a été trouvée. Mots clés: Surdité Neurosensorielles, DFNB1, DFNB2, Marqueurs Microsatellites