Spectrum and frequency of GJB2 mutations in a cohort of 264 Portuguese nonsyndromic sensorineural hearing loss patients.

Objective: To assess the spectrum and prevalence of mutations in the GJB2 gene in Portuguese nonsyndromic sensorineural hearing loss (NSSHL) patients.

Design: Sequencing of the coding region, basal promoter, exon 1, and donor splice site of the GJB2 gene; screening for the presence of the two common GJB6 deletions.

Study Sample: A cohort of 264 Portuguese NSSHL patients.

Results: At least one out of 21 different GJB2 variants was identified in 80 (30.2%) of the 264 patients analysed. Two mutant alleles were found in 53 (20%) of these probands, of which 83% (44/53) harboured at least one c.35delG allele. Twenty-seven (10.2%) of the probands harboured only one mutant allele. Subsequent analysis revealed that the GJB6 deletion del(GJB6-D13S1854) was present in at least 7.4% (2/27) of the patients carrying only one mutant GJB2 allele. Overall, one in five (55/264) of the patients were diagnosed as having DFNB1-related NSSHL, of which the vast majority (53/55) harboured only GJB2 mutations.

Conclusions: This study provides clear demonstration that mutations in the GJB2 gene are an important cause of NSSHL in Portugal, thus representing a valuable indicator as regards therapeutical and rehabilitation options, as well as genetic counseling of these patients and their families.