Cohen, Mazal; (1999) Auditory and vestibular studies in families with autosomal recessive non-syndromic hearing loss. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Autosomal recessive non-syndromic hearing loss (ARNSHL) is the most common cause of genetic profound pre-lingual hearing impairment. In recent years, a breakthrough in genetic research has lead to advances in mapping genes causing this condition and in elucidating their function. This progress brought about improvements in rehabilitation, counselling and development of preventative medical options, but to take advantage of these developments, early diagnosis is essential. This study was undertaken with the view to establishing whether, as an adjunct to genetic research, distinct auditory and vestibular phenotypic characteristics, breeding true within a sibship, might be identified, that would contribute to the resolution of genetic heterogeneity of the condition. Twelve families, in whom ARNSHL was ascertained, were studied. In the affected children (n=23) a pre-lingual severe or profound (> 80 dB) non-progressive hearing loss was the most common form. In a third of subjects, balance and/or vestibular deficits were identified, however, these were predominantly mild and lacked the specificity required for sub- classifying ARNSHL cases in whom the audiometric profile is uniform. A detailed audiometric protocol was also constructed with the aim of exploring the possibility of detecting asymptomatic carriers of mutant genes causing deafness from their audiometric profiles. Auditory aberrations were found in more than half of the carriers (14/24). Pure-tone audiometry and otoacoustic emissions emerged as the most sensitive tests, and, pending further studies, may be implemented in screening clinically normal hearing individuals at risk of carrying mutations that cause deafness. Furthermore, it is envisaged that the detailed appraisal of each test would contribute significantly to the emergence of a standardised investigation protocol in genetic hearing impairment. A phenotypic-genotypic correlation in three families with mutations in the GJB2 gene revealed a highly variable audio-vestibular phenotype in the affected children, although in 4/6 obligate carriers, no auditory aberrations were detected.

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