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/hhh 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.