Audiological profile of the prevalent genetic form of childhood sensorineural hearing loss due to GJB2 mutations in northern Greece

The present study describes the audiological profile of genetic hearing loss resulting from GJB2 mutations in northern Greece, as this represents the most frequent single cause of childhood sensorineural hearing loss. The 35delG mutation in homozygosity was detected in 27 of 107 patients (25.2%). The audiological profile is that of a profound or severe sensorineural hearing loss, with a sloping or flat configuration of the audiogram, mostly symmetrical, non-progressive and affecting more the higher frequencies. This profile underlines the importance of early identification and genetic family counseling leading to the future possibility of prevention of deafness.

Prelingual nonsyndromic hearing loss in Greece. Molecular and clinical findings

Mutations in the gene encoding the gap-junction protein connexin 26 (GJB2) on chromosome 13q11 have been shown as a major contributor to prelingual, sensorineural, nonsyndromic deafness. One specific mutation, 35delG, has accounted for the majority of the mutations detected in the GJB2 gene in Caucasian populations and is one of the most frequent disease mutations identified so far with highest carrier frequency of 3,5% in the Greek population. In a collaboration with the major referral centers for childhood deafness in Greece, patients were examined by an extensive questionnaire to exclude syndromic forms and environmental causes of deafness and by allele-specific PCR for the detection of the 35delG mutation. The 35delG mutation was found in 32.1% of the alleles in 173 unrelated cases of prelingual deafness: 50 homozygotes and 11 heterozygotes. Individuals heterozygous for the 35delG mutation were further analyzed by direct genomic sequencing of the coding region of the GJB2 gene, which revealed R184P and 486insT mutations in single alleles. We conclude that the 35delG GJB2 mutation is responsible for one third of prelingual, sensorineural deafness in Greece, which is higher than the usually quoted 20% for Caucasian populations.