Genetic causes of hearing loss.

In the past year, genes involved in the branchio-oto-renal and Treacher-Collins syndromes were cloned. Myosin 7A, a gene previously implicated in Usher syndrome type 1B, was also found to be mutated in non-syndromic hearing loss. Likewise, linkage studies in Pendred syndrome and Usher syndrome type 1D suggest that allelic mutations can cause syndromic and non-syndromic forms of deafness. In patients with X-linked deafness type 3, a hotspot for deletions was found 900 kb proximal to the causal gene POU3F4. Most importantly, the connexin 26 gene is mutated in approximately 50% of all recessive deafness families, enabling early diagnosis and carrier detection.