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Hereditary hearing impairment (HHI) is a heterogeneous class of disorders showing various patterns of inheritance and involving a multitude of different genes. Neurosensory hearing impairment is one of the most common human sensory disorders affecting one in 1000 children with at least 60% of cases being inherited. The mode of inheritance of non-syndromic hearing disorders can be assigned to autosomal dominant (10-15%), autosomal recessive (70%), X-linked (1-3%) and mitochondrial forms (6-37% out of all cases). Syndromal hearing defects are categorized according to the underlying defects and contain more than 700 syndromes. In daily practice, non-syndromic hearing impairment (NSHL) is predominant and accounts for up to 70% of all inherited sensorineural hearing defects. Although our knowledge of genes being involved in the development of HI accumulated during the past five years, little is known about the molecular basis of normal auditory function. To date, 24 genes for non syndromic HI and an even larger number of genes for syndromic HI have been identified. These genes play important roles for the normal inner ear: in the development, structure, ion exchange and further physiological function. This review presents a summary of known genes and new candidates, their possible role and the current state of knowledge in genetics of hereditary hearing impairment, all of them possibly expected to allow for new concepts in therapy. more...