Vol.96 No.11 contentsPRACTICA OTO-RHINO-LARYNGOLOGICA
Vol. 96 No.11 November 2003
Deafness Genes and Ear Disease
Ken Kitamura, Yoshihiro Noguchi and Hisashi Tokano
(Tokyo Medical and Dental University)
Katsumasa Takahashi
(Gunma University)
Yuya Tamagawa
(Jichi Medical School)
The pathophysiology of sensorineural hearing loss, which is a common clinical disorder, remains to be determined. Many genes responsible for sensorineural hearing loss have been identified during the last decade, and the underlying mechanisms causing hearing loss have begun to be clarified due to recent developments in molecular genetics. In this review article, deafness genes are briefly described. We also presented our recent study of the histopathology of the temporal bone from a patient with MELAS (mitochondrial encephalopathy, lactic acidosis and stroke-like episodes) as well as quantitative analysis of mitochondrial DNA (mtDNA) mutation at nucleotide 3243 in the inner ear, and a new deafness gene (sans) identified in the Jackson shaker mouse.
To date, 51 autosomal dominant, 39 autosomal recessive, and 8 X-linked nonsyndromic sensorineural hearing impairment loci have been mapped and 34 genes have been identified. Histopathological examination of the temporal bone from a patient with MELAS demonstrated severe degeneration of the stria vascularis and degenerative changes in spiral ganglion cells. Quantitative DNA studies showed high amounts of mutant mtDNA in the inner ear. The Jackson shaker (js) mouse carried a recessive mutation causing phenotypes such as deafness, abnormal behavior (circling and/or head-tossing) and degeneration of inner ear neuroepithelia. Two alleles have been identified to date, the original js and jsseal. A gene encoding new scaffold-like protein Sans was identified to show mutations in the two js mutants. Sans were highly expressed in the inner and outer hair cells of the cochlea, where abnormalities are found in js mice. The Sans protein was expected to mediate protein-protein interactions with cytoskeletal structures that might be involved in signal transduction in the cochlear hair cells. Mutations of SANS in the human ortholog were demonstrated to cause Usher 1G syndrome.
Key words : deafness, gene, mutant mouse, MELAS, mitochondrial DNA