**3. Auditory neuropathy spectrum disorder (ANSD)**

One disorder that continuously eludes the new born hearing screen is ANSD. ANSD represents a range of hearing disorders of variable severity which present with pure tone hearing thresholds that may be low or approach normal, but underestimate the subject's perception of hearing difficulty. Included within the spectrum are inner hair cell anomalies, neuropathy of the auditory nerve, disruption of the olivocochlear response (OCR), and brainstem dysfunction that can be secondary to kernicterus (Amatuzzi et al., 2001; Berlin et al., 2005; Harrison, 1998; Hood & Berlin, 2001; Shapiro, 2003; Starr, Picton, Sininger, Hood, & Berlin, 1996; Yasunaga et al., 1999).The unifying feature of ANSD diseases are a characteristic finding of abnormal ABR waveforms in the presence of normal OAE and/or cochlear microphonic (CM). Middle ear muscle reflexes and the olivocochlear reponse are also absent. These findings are suggestive of persistent outer hair cell activity but lack of a normal afferent auditory pathway and as such would be missed by currently employed screening methods (Manchaiah et al., 2011). Accurate diagnosis is hampered by the lack of a simple commercially available test for OCR function but typically the diagnosis can be assumed from OAE and ABR results alone.

Etiologies of ANSD that have been identified include polyneuropathy (especially in adults), perinatal anoxia and hypoxia, and hyperbilirubinaemia, congenital brain anomalies, ototoxic drug exposure, and genetic factors. An estimated 40% of cases have an underlying genetic basis, which can be inherited in both syndromic and non-syndromic conditions (Harrison, 2001; Manchaiah et al., 2011; Nadol Jr, 2001; Starr et al., 1996).

Treatment options in ANSD include auditory verbal therapy, cued speech, hearing aids and cochlear implantation (Cone-Wesson, Rance, & Sininger, 2001; Rance & Barker, 2008a; Hood & Berlin, 2001). Prognostication and predicting treatment outcome is difficult and varies depending on origin. Some forms of neonatal ANSD can show significant spontaneous improvement (Attias & Raveh, 2007; Rance & Barker, 2008b). As such determination of patient who will benefit from hearing aids or cochlear implantation is difficult (Raveh, Buller, Badrana, & Attias, 2007). The development of improved testing techniques that can be used to diagnose, characterize, and differentiate between the numerous diseases that make up this spectrum may allow patients to be treated earlier.
