1. ¹Department of Medical Biochemistry and Genetics, Wilhelm Johannsen Centre for Functional Genomics, University of Copenhagen, Copenhagen, Denmark
2. ²Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI, USA
3. ³Department of Medical Genetics, University Hospital, Tromsø, Norway
4. ⁴The Kinase Signalling Laboratory, Biotech Research and Innovation Centre, Copenhagen, Denmark
5. ⁵Cancer Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD, USA
6. ⁶Institute of Genetic Medicine, Johns Hopkins University, Baltimore, MD, USA
7. ⁷Department of Human Genetics, University of Pittsburgh, Pittsburgh, PA, USA
8. ⁸Department of Otorhinolaryngology, University Hospital of Oslo, Oslo, Norway
9. ⁹Neurogenomics Division, Translational Genomics Research Institute, Phoenix, AZ, USA
10. ¹⁰Department of Audiology, H:S Bispebjerg Hospital, Copenhagen, Denmark

Correspondence: Dr L Tranebjærg, Department of Audiology, H:S Bispebjerg Hospital, Bispebjerg Bakke 23, DK-2400 Copenhagen NV, Denmark. Tel: +45 35 316341; Fax: +45 35 313951; E-mail: tranebjaerg@imbg.ku.dk

Received 9 November 2005; Revised 24 April 2006; Accepted 25 April 2006; Published online 14 June 2006.

Abstract

The -actin gene (ACTG1) encodes a major cytoskeletal protein of the sensory hair cells of the cochlea. Recently, mutations in ACTG1 were found to cause autosomal dominant, progressive, sensorineural hearing impairment linked to the DFNA20/26 locus on chromosome 17q25.3 in four American families and in one Dutch family. We report here the linkage of autosomal dominant, progressive, sensorineural hearing impairment in a large Norwegian family to the DFNA20/26 locus. Sequencing of ACTG1 identified a novel missense mutation (c.1109T>C; p.V370A) segregating with the hearing loss. Functional analysis in yeast showed that the p.V370A mutation restricts cell growth at elevated temperature or under hyperosmolar stress. Molecular modelling suggested that the p.V370A mutation modestly alters a site for protein–protein interaction in -actin and thereby modestly alters -actin-based cytoskeletal structures. Nineteen Norwegian and Danish families with autosomal, dominant hearing impairment were analyzed for mutations in ACTG1 by sequencing, but no disease-associated mutations were identified. Finally, a long-term follow-up of the hearing loss progression associated with the p.V370A mutation in ACTG1 is provided. The present study expands our understanding of the genotype–phenotype relationship of this deafness gene and provides a sensitive and simple functional assay for missense mutations in this gene, which may assist future molecular diagnosis of autosomal-dominant hearing impairment. Finally, the present results do not indicate that mutations in ACTG1 are a frequent cause of autosomal-dominant postlingual sensorineural hearing impairment in Norway nor Denmark.