HUMAN MUTATION Mutation in Brief #935 (2006) Online MUTATION IN BRIEF © 2006 WILEY-LISS, INC. Received 24 May 2006; accepted revised manuscript 18 July 2006. Deficient Membrane Integration of the Novel p.N14D- GJB2 Mutant Associated With Non-Syndromic Hearing Impairment B. Haack 1 *†, K. Schmalisch 2 †, M. Palmada 2 , C. Böhmer 2 , N. Kohlschmidt 3 , A. Keilmann 4 , U. Zechner 3 , A. Limberger 4 , S. Beckert 5 , H.P. Zenner 6 , F. Lang 2 , and S. Kupka 5 1 Department of Molecular Pathology, University Hospital of Tübingen, Germany; 2 Institute of Physiology, University of Tübingen, Germany; 3 Institute of Human Genetics, Johannes Gutenberg University Mainz, Mainz, Germany; 4 Department of Communication Disorders, Johannes Gutenberg University Mainz, Mainz, Germany; 5 Department of General and Transplant Surgery, University Hospital of Tübingen, Germany; 6 Department of Otolaryngology, University Hospital of Tübingen, Germany †These authors contributed equally to this work and thus share first authorship. * Correspondence to: Dr. Birgit Haack, Department of Molecular Pathology, University Hospital of Tübingen, Liebermeisterstr. 8, 72076 Tübingen, Germany; Tel.: +49 7071 29 83120; Fax: +49 7071 29 5334; E-mail: birgit.haack@med.uni-tuebingen.de Grant sponsor: This study was supported by the fortüne programme (1028-0-0) Tübingen. Communicated by Dvorah Abeliovich Mutations in GJB2, the gene encoding for the Gap Junction protein Connexin 26 (Cx26), have been established as the major cause of hereditary, non-syndromic hearing impairment (HI). We report here the identification of a novel point mutation in GJB2, c.40A>G [p.N14D], detected in compound heterozygosity with the c.35delG mutation in two brothers with moderate non-syndromic sensorineural HI. The mother who carried one wildtype and a p.N14D allele displayed normal hearing. The mutation leads to substitution of the neutral amino acid asparagine (N) by the negatively charged aspartic acid (D) at amino acid number 14, a position that is conserved among Cx26 of different organisms and among many other connexin isoforms. To investigate the impact of this mutation on protein function, Cx26 activity was measured by depolarization activated hemichannel conductance in non-coupled Xenopus laevis oocytes. Oocytes injected with the p.N14D mutant cRNA showed strongly reduced currents compared to wildtype. Coinjection of wildtype and mutant cRNA at equimolar levels restored the conductive properties supporting the recessive character of this mutation. Total Cx26 protein expression and cell surface abundance examined by western blotting and by quantitative immunoassays revealed that the hemichannel was properly synthesized but not integrated into the plasma membrane. In this study we have shown that the GJB2 mutation p.N14D is associated with recessively inherited HI and exhibits a defective phenotype due to diminished expression at the cell surface. © 2006 Wiley- Liss, Inc. KEY WORDS: gap junction; connexin; Cx26; mutation; N14D; Xenopus laevis; oocytes; functional characterization INTRODUCTION Hearing impairment (HI) represents the most frequent neurosensory disorder and the majority of hearing deficiencies are of genetic origin. The hereditary cases mainly manifest as non-syndromic HI that means HI DOI: 10.1002/humu.9464