Molecular genetic aspects of non-syndromic hearing loss in India

Abstract

In the last decade or so, advances in the areas of human genetics and cell biology have provided a major insight into the molecular mechanisms involved in the development, function and dysfunction of the auditory system. In contrast to the visual or olfactory systems, in which reasonable amounts of sensory tissue can be gathered, the auditory system has proven difficult to access through biochemical studies, mainly because very small amounts of suitable tissue are available for analysis. For example, the retinal contains about 120 million photo-receptor cells, whereas the cochlea contains only about 10 4 hair cells. Moreover, key regulatory molecules, such as the transduction channel proteins, may be present in only a few tens of copies per sensory hair cell of the cochlea, compounding the difficulty. On the other hand, genetic approaches for understanding auditory system have led to the identification of several key molecules, as this approach makes no assumptions about the nature or expression level of molecules essential for the process of normal hearing physiology. Progress in deafness genetics is evident from the fact that in the year 1995, POU3F4 was the first gene identified for non-syndromic hearing loss (NSHL), and in a decade’s time, mutations in 40 different genes have been implicated in human NSHL (Petit et al. 2001; Friedman and Griffith, 2003). The rapid progress in gene discovery in the auditory system has been greatly facilitated by: (i) the availability of substantially annotated human and mouse genomes, and (ii) a combination of forward and reverse genetic approaches to create mouse models of non-syndromic deafness.