Genetic type of progressive hearing loss [Ipoacusie progressive di tipo genetico.]

In daily practice we tend to underestimate hereditary factors as a cause of hearing impairment especially in those cases of late-onset and progressive hearing loss. Genetic hearing impairment may be congenital but it also may develop at any decade throughout life or deteriorate as part of a pre-existing congenital or acquired hearing impairment. Over the past 5 years, hereditary diseases associated with hearing impairment have been mapped, and several of genes have already been identified. Identification of genes causing hereditary deafness, as with other genetic diseases, goes through two stages: first mapping, then cloning. One method used to identify candidate genes based on their function or pattern of tissue expression involves the construction of cDNA libraries from the target organ or tissue, in this case from the cochlea. Studies of the molecular genetics of the inner ear are hampered by its relative inaccessibility, by the limited numbers of cochlear and vestibular cells, and by our inability to maintain many of these cell types in long term culture. The construction and characterization of cochlear cDNA libraries from humans and other species provide an important resource for rapid identification of cochlear genes involved in normal hearing and in hearing disorders; cDNA libraries constructed at different stages of development, and subtracted from each other, could be instrumental in identifying genes important at each stage of development of the cochlea. Libraries made from different tissues within an organ (i.e. inner vs outer hair cells) could be compared to identify genes that are needed for the differentiation of the cells into specific types. In addition, these libraries have the potential to foster identification of other proteins unique to the cochlea and will contribute to the identification, characterization, and functional analysis of these cochlea-specific proteins. Another important application of cDNA libraries is for identifying hearing loss genes. Once the candidate gene for a given type of hearing loss is cloned and decoded, the structure of its protein product can be determined. This will provide insights into biochemical function of the gene product in normal cochlear tissue, and will show why the genetic mutation result in hearing loss. Pedegree analysis and audiometric morphology have been widely used to attempt a subcategorisation of many isolated or familial "genetic" cases. A debatable point is the influence of aging on a genetic hearing loss. Effects due to genetic factors are often not easily distinguishable from the age-related factors. According to our findings, the progression of hearing loss present in several different patterns, according to the different interactions between hereditary hearing loss and presbycousis.