Hearing loss is the most common congenital disorder in the world, and up to 60% of all cases have a genetic background. Of these, around 70% are non-syndromic. The most common genetic variant causing hearing loss in European and Mediterranean population, is the c.35delG variant in the GJB2 gene in homozygous state. Due to the high frequency of this variant, the aim of this study was to determine the differences in the hearing status and the type of auditory rehabilitation of the deaf and hard of hearing people in Slovenia, who are homozygous for c.35delG mutation in the GJB2 gene, as well as to determinate their speech intelligibility in everyday life.
In this study, we included a cohort of 65 people, who were previously confirmed to have the c.35delG mutation in the GJB2 gene in a homozygous state, and who are managed at the Clinic for Otorhinolaryngology and Cervicofacial Surgery at the University Clinical Center of Ljubljana. Data on hearing status, progression and type of auditory rehabilitation were obtained at the clinic in the persons' medical records. To determine their speech intelligibility, we used the Intelligibility in Context Scale for Slovenian (ICS).
We found that there are differences in both the severity of hearing loss as well as the onset of hearing loss in our cohort. The severity of hearing loss ranged from moderate to profound, with the latter being the most prevalent (70,7% of our cohort), while the onset of hearing loss was mostly prelingual (80% of the cohort). We also confirmed that there are differences in the type of hearing (re)habilitation of the people in our cohort, since 61,5% of people with this mutation are cochlear implant users, while the remaining 38,5% use conventional hearing aids. We have also proven the statistically significant difference between the first and last hearing measurement (the results of PTA or ABR/ASSR), thereby proving a statistically significant decline in hearing (progression) in the cohort.
With the ICS scale, we determined the speech intelligibility of the people included in this study. When comparing speech intelligibility according to the type of hearing (re)habilitation, we could not demonstrate a statistically significant difference in speech intelligibility between cochlear implant users and conventional hearing aid users. We also did not find a statistically significant correlation between the level of speech intelligibility in deaf or hard-of-hearing children (up to 18 years old) with this mutation and the duration of deafness. We can therefore conclud that longer period between the onset of deafness and implantation does not necessarily mean a lower level of intelligibility of a person's speech.
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