Fine structure DPOAEs in normal hearing consanguineous parents of congenitally hearing impaired siblings (probable carriers)

Abstract

Background: This study examines the concealed phenotypic variations in carriers of non-syndromic recessive hearing loss, using fine structure distortion product otoacoustic emissions (DPOAEs). As genetic tests were not feasible to validate the recessive trait in the participants, an inclusion criterion was followed, where in normal hearing parents with two or more hearing-impaired children and a positive consanguinity were assumed to be probable carriers. Materials and Methods: The amplitude of fine structure DPOAEs from 27 ears of probable carriers was compared with 62 normal control ears. The primaries were presented at 65/55dBSPL, maintaining a frequency ratio of 1.2, covering 20 points per octave across 1-4 kHz. A comparison between the octaves 1-2 kHz and 2-4 kHz was also made in all the participants to observe if the deviant functioning of the hair cells predominated the higher or the lower frequencies. Results: The overall fine structure amplitude was significantly reduced in the probable carrier group across the frequencies. There was a significant difference between 1-2 kHz and 2-4 kHz in both non-carriers and probable carriers. The higher frequencies had a lower amplitude and the lower frequencies had a higher amplitude. The probable carrier group had a relatively significant amplitude reduction in the higher octave when compared to the control group. Conclusion: Carriers of hearing loss do exhibit subtle functional changes in the ear, in spite of having a normal hearing sensitivity. This study throws light on the scope of fine structure emissions to emerge as a very good diagnostic tool in the field of audiology.