Original article A new large deletion in the DFNB1 locus causes nonsyndromic hearing loss Delphine Feldmann a, * , Ce ´ dric Le Mare ´ chal b , Laurence Jonard a , Patrick Thierry c , Ce ´ cile Czajka d , Remy Couderc a , Claude Ferec b , Françoise Denoyelle e , Sandrine Marlin f , Florence Fellmann g a Laboratoire de Biochimie, INSERM, U587, Centre de Re ´fe ´rence des Surdite ´sGe´ne´tiques,AP-HP,Ho ˆpital Armand-Trousseau, 26 Avenue du Docteur-Arnold-Netter, 75012 Paris, France b Institut National de la Sante´ et de la Recherche Me´dicale (INSERM), U613, Brest, France c Service de Pe´diatrie, Centre Hospitalier, Vesoul, France d Service d’ORL-Audiophonologie et de Chirurgie Cervico-Faciale, Ho ˆpital Jean-Minjoz, Besançon, France e Service d’ORL Pe ´diatrique et de Chirurgie Cervico-Faciale, INSERM, U587, Centre de Re ´fe ´rence des Surdite ´sGe´ne´tiques,AP-HP,Ho ˆpital Armand-Trousseau, Paris, France f Service de Ge ´ne´tique, INSERM, U587, Centre de Re ´fe ´rence des Surdite ´sGe´ne´tiques,AP-HP,Ho ˆpital Armand-Trousseau, Paris, France g Service de Ge ´ne ´tique Me´dicale, CHUV, Lausanne, Switzerland article info Article history: Received 20 June 2008 Accepted 30 November 2008 Available online 13 December 2008 Keywords: Deafness GJB2 Connexin 26 Hearing impairment DFNB1 V84M GJB6 Deletion abstract Mutations in the GJB2 gene encoding the gap junction protein connexin 26 are responsible for up to 30% of all cases of autosomal recessive nonsyndromic hearing impairment (HI) with prelingual onset in most populations. The corresponding locus DFNB1, located on chromosome 13q11–q12, is also affected by three distinct deletions. These deletions extended distally to GJB2, which remains intact. We report a novel large deletion in DFNB1 observed in a patient presenting profound prelingual HI. This deletion was observed in trans to a GJB2 mutated allele carrying the p.Val84Met (V84M) mutation and was shown to be associated with hearing loss. The deletion caused a false homozygosity of V84M in the proband. Quantification of alleles by quantitative fluorescent multiplex PCR (QFM-PCR) enabled us to study the breakpoints of the deletion. The deleted segment extended through at least 920 kb and removed the three connexin genes GJA3, GJB2 and GJB6. The distal breakpoint inside intron 2 of CRYL1 gene differed from the breakpoints of the known DFNB1 deletions. This case highlights the importance of screening for large deletions in molecular studies of GJB2. Ó 2008 Elsevier Masson SAS. All rights reserved. 1. Introduction Mutations in the GJB2 gene (MIM#121011) encoding the gap junction protein connexin 26 (CX26) are the most frequent cause of congenital nonsyndromic hearing impairment (NSHI) [1]. The hearing impairment caused by recessive GJB2 mutations is char- acterized by prelingual onset, and bilateral NSHI. The severity of the deafness varies from mild to profound and may even vary among siblings [2,3]. The GJB2 gene located on chromosome 13q11–q12 contains two exons. The coding sequence is located in the second exon and has been extensively studied. More than 100 mutations have been reported in exon 2, whereas only one mutation has been described in the donor splice site of intron 1 (Ballana et al. Con- nexins and Deafness, http://www.crg.es/deafness). Although most of the mutations are rare or private, some mutations are prevalent in specific populations, such as 35delG in Northern and Southern Europeans and also Caucasian-American populations [3–5], 167delT in Ashkenazi Jews [6], 235delC in East Asians [7], W24X in Spanish and Slovak Romany populations [8,9], and R143W in Africans [10]. The IVS1 þ1G > A mutation disrupting the donor splice site of intron 1 has also been frequently observed in Hungarian, Czech and Turkish patients [11,12]. In addition to recessive GJB2 mutation, rare GJB2 mutations have been described as dominant acting alleles. These mutations can be responsible for HI alone or HI associated with skin disorders [13,14]. Recently, it has been demonstrated that the recessive deafness locus DFNB1 (MIM#220290) in 13q11–q12 corresponding to GJB2 must be extended to more telomeric regions of GJB2: some indi- viduals with NSHI mapping to this locus have a deletion in 13q12 [15–17]. This deletion, named del(GJB6-D13S1830), was found to segregate with the HI and has been observed in rare homozygous patients or more frequently in patients with one GJB2 mutated allele in trans. The deletion del(GJB6-D13S1830) removes 309 kb, partially including GJB6, which encodes connexin 30 and CRYL1 [17]. The del(GJB6-D13S1830) deletion represents the most frequent mutation after 35delG in certain populations of DFNB1 * Corresponding author. Tel.: þ33 (0)1 44 73 68 67; fax: þ33 (0)1 44 73 66 87. E-mail address: delphine.feldmann@trs.aphp.fr (D. Feldmann). Contents lists available at ScienceDirect European Journal of Medical Genetics journal homepage: http://www.elsevier.com/locate/ejmg 1769-7212/$ – see front matter Ó 2008 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.ejmg.2008.11.006 European Journal of Medical Genetics 52 (2009) 195–200