It is estimated that about 1 in 500 children are born with a significant hearing loss.1 Non-syndromic recessive hearing loss (NSRHL) represents a major aetiologic factor in childhood hearing loss since it accounts for approximately 40% of all cases.2 Many of these genetic forms of hearing loss are indistinguishable with current clinical methods. Even so, more than 12 recessive genes have been identified primarily from large consanguineous pedigrees (see the Hereditary Hearing Loss Homepage http://www.uia.ac.be/dnalab/hhhTest for an overview). By definition, non-syndromic suggests a “simple” phenotype limited to hearing loss with no other associated symptoms. However, hearing is a complex process. Since a hearing defect might occur at any place along the auditory pathway, it would seem reasonable to expect to be able to differentiate types of NSRHL based on the location where the auditory process is disrupted. Indeed, new audiological testing strategies now give insight into the point where such defects have occurred. Pure tone audiometry has been the standard method used to measure hearing threshold but, since it subjectively tests the overall integrity of the auditory pathway, it gives only limited information about where that pathway is failing. The auditory brainstem response (ABR) is an objective measure of the overall auditory transduction process. The otoacoustic emissions (OAEs) test is another objective measure of the auditory pathway, which detects responses of the outer hair cells (OHCs) to environmental sound.3–6 A good review of auditory tests can be found in Hood.7 Some children have a hearing loss based on pure tone audiometry and ABR, but with normal OAEs. This type of hearing loss has been defined as auditory neuropathy (AN).8 Subjects with AN can have varying degrees of hearing loss with poor speech reception out of proportion to the degree of hearing loss. In contrast …
