A novel hearing loss-related mutation occurring in the GJB2 basal promoter

Abstract

Mutations in the GJB2 gene are a major cause of nonsyndromic recessive hearing loss in many countries. In a significant fraction of patients, only monoallelic GJB2 mutations known to be either recessive or of unclear pathogenicity are identified. This paper reports a novel GJB2 mutation, 23438CRT, found in the basal promoter of the gene, in trans with V84M, in a patient with profound hearing impairment. This novel mutation can abolish the basal promoter activity of GJB2. These results highlight the importance of extending the mutational screening to regions outside the coding region of GJB2.

A novel M163L mutation in connexin 26 causing cell death and associated with autosomal dominant hearing loss

“…The novel M163L mutation was confirmed by PCR, using the primers Cx26-17(F) and Cx26-5 (R) (Scott et al, 1998), followed by enzymatic restriction with the enzyme PstI (New England Biolabs) in a 20 lL reaction volume at 37°C for 3 h. The same enzymatic restriction analysis was carried out in 103 non-related normal hearing control individuals from the Portuguese population. Mutational screening of GJB2 basal promoter, exon 1 and donor splice site was performed according to Matos et al (2007).…”

“…The construct encoding wild-type Cx26 and constructs encoding eGFP, eGFP-tagged V84M-Cx26, eGFP-tagged D50N-Cx26 and eCFP-tagged wtCx26 or wtCx30, were also used. V84M is a Cx26 non-syndromic hearing loss mutation (Matos et al, 2007) and D50N is a Cx26 syndromic skin disease-associated mutation that induces cell death in vitro (Common et al, 2004).…”

Identification and genotype/phenotype correlation of mutations in a large German cohort with hearing loss

“…This raises the suggestion that a second mutation in GJB2 was not detected by sequencing (mutation in promoter region, intronic mutation or splicing site mutation) or that the presence of mutations in other genes not tested in this study is causative for hearing loss. This relative high frequency of monoallelic 35delG mutations has indeed been noticed previously [48][49][50]. Referring to promoter defects in GJB2 as a possible explanation for this fact Pollak et al [48] did not reveal sequence alterations in the promoter region of GJB2 whereas Matos et al(2007) detected a basal promoter mutation which can abolish the promoter acitivity of GJB2.…”

“…This relative high frequency of monoallelic 35delG mutations has indeed been noticed previously [48][49][50]. Referring to promoter defects in GJB2 as a possible explanation for this fact Pollak et al [48] did not reveal sequence alterations in the promoter region of GJB2 whereas Matos et al(2007) detected a basal promoter mutation which can abolish the promoter acitivity of GJB2. Alongside, standard PCR amplification of exon 2 for sequencing analysis is unable to detect gross deletions or sequence variations in the promoter site or the transcription regulating regions.…”

Diagnostic pitfalls for GJB2‐related hearing loss: A novel deletion detected by Array‐CGH analysis in a Japanese patient with congenital profound hearing loss

“…The absence of the transcriptional promoter sequence is thought to abolish GJB2 gene transcription. Previous functional studies of c.‐22‐2A>C (a splice‐site mutation) and g.‐77C>T (a mutation of the basal promoter region) did not yield any detectable Cx26 protein or mRNA,13, 14 suggesting that no GJB2 transcripts would be produced from this deletion allele. The proband's father, harboring a heterozygous 8 kb deletion, is not conscious of any hearing loss, implying that the novel long deletion is a pathogenic variant in autosomal recessive inheritance HL.…”