Genetic
Heterogeneity
The most important insight that has emerged from research on genetic deafness during the past 40 years is the recognition that changed genes at many different chromosomal locations can cause deafness. Hundreds, perhaps thousands, of genes may be required to provide the instructions to form an ear that can hear. Therefore, changed genes at any one of the many different chromosomal locations may have the same or a similar effect -- hearing loss.
The many forms of syndromic deafness provide a dramatic example of this heterogeneity, where genetically distinct forms of deafness can be recognized because of differences in the associated clinical features. However, a specific form of syndromic deafness can be recognized in only about 20-30% of families with deafness. In the remaining cases, hearing loss is the only recognizable effect of the changed gene.
Even among these cases, we now know that changed genes at many different
chromosomal locations can cause non-syndromic
(isolated) hearing loss.
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