Trends in Genetics
OutlookDeafness genes: expressions of surprise
Section snippets
Clinical features suggest a complex story
Interestingly, some genes are associated both with syndromic and with non-syndromic deafness, such as MYO7A (encoding an unconventional myosin molecule, in which mutations can lead either to Usher syndrome or to non-syndromic deafness), and PDS (which is involved in Pendred syndrome and non-syndromic deafness). Furthermore, the same gene can be involved both in dominant and in recessive non-syndromic deafness; GJB2 (encoding Connexin 26), TECTA and MYO7A are examples of this.
The report of
Interacting genes can influence the extent of hearing impairment
It is emerging that only limited information can be gained about the likely nature of the responsible gene from audiological features: mutations in a specific gene can lead to a range of severity of hearing impairment, from mild to profound, congenital to late-onset progressive, even when the same mutation is involved. Examples of this include Waardenburg syndrome (e.g. PAX3 or MITF) and DFNB1 (GJB2), in which affected family members with the identical mutation can show a range of hearing
Highly specific expression patterns
The tables document reports of expression of these deafness genes in the normal ear, and there are some surprises here (Fig. 1). The sensory hair cells of the cochlea of the inner ear are the primary receptor cells, transducing the vibrational energy of sound into electrical changes, which in turn trigger action potentials in the cochlear nerve. Hair cells are highly specialized cells, so one might have imagined that much human genetic deafness would be due to mutations in genes expressed in
Acknowledgements
We thank Dr A. Kiernan for preparing the artwork, Drs Petit, Forge, Edwards, Everett, Wu, Green, Chen and Corey for their kind permission to use their data before publication, and Prof. S. Brown for many helpful discussions. The work was supported by the MRC, the European Commission, and Defeating Deafness.
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