ABSTRACT
The development of the normal ear is an extremely complex process, owing to the diversity of tissues and cells that are present in the ear compared to some other organs. The outer, middle, and inner ear consist of several different tissues, each of which in turn contains highly diverse cell types. The formation and differentiation of these cell types must occur in a precisely coordinated manner, to result in the intricate structures and complex functional capabilities of the ear. The number of genes that are involved in ear development presumably reflects this tissue and cellular diversity. It is not unreasonable to assume that the coordinated expression of thousands of genes occurs during the development of the ear. Among these, it seems likely that hundreds of genes play a direct role in regulating inner ear development, and the number may be even greater (91, 112). These genes provide a major substrate for inherited hearing loss. Indeed, mutations that disturb the normal process of ear development appear to account for the majority of inherited deafness.
