The majority of hereditary congenital deafness is due to autosomal recessive mutations. Many of these mutations cause no other obvious phenotypic alterations. The total number of different recessive mutant genes causing nonsyndromal deafness has been estimated to be tween 20 and 2,000. To date, three different genes causing nonsyndromal deafness in humans have been mapped but not cloned. Consequently, the primary defects caused by these genes remain unknown. In the geographically and ethnically isolated Balinese village of Bengkala, approximately 2% of the villagers have congenital nonsyndromal deafness. As a response to the prevalence of deafness in Bengkala, villagers developed a unique sign language that integrates the deaf and hearing members of this community. An interdisciplinary approach involving anthropology and molecular genetics is being used to study deafness in Bengkala, Bali. This grant proposal focuses exclusively the molecular genetics and developmental biology of deafness. Segregation analysis indicates that congenital profound neurosensory deafness in Bengkala is due to a single autosomal recessive mutant allele of the DFNB3 gene. The DFNB3 gene was mapped to the pericentromeric region of chromosome 17 using a novel strategy, allele-frequency-dependent homozygosity mapping (AHM). After identifying several genetic markers that are very closely linked to DFNB3, a high resolution refined genetic map and YAC contig of the DFNB3 region were constructed. Flanking markers restrict DFNB3 to an approximately 3 Mb region of 17p. The goals of this project are: (1) identify blanking markers that are more closely linked to DFNB3, (2) clone and characterize the DFNB3 gene, (3) develop a mouse model for the mutation in DFNB3 by evaluating existing candidate genes or clone the murine homolog. Based on present mapping information the shaker-2 mouse is a good candidate since shaker-2 maps to chromosome 11 in a region of conserved synteny with the 17p region to which we have mapped DFNB3, (4) use the mouse model of DFNB3 to determine the normal developmental expression pattern of mRNA transcribed from the murine homolog, Dfnb-3, and (5) also using the mouse model with a focus on inner ear development, determine the biological mechanism causing hereditary deafness due to mutations in Dfnb-3 and thus, the like explanation for deafness in Bengkala. Our molecular genetic analysis of deafness in Bengkala will yield insights into an essential biological processes required for the normal development of the auditory system and insights into the molecular pathology of autosomal recessive hereditary deafness.
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