**4.1 Different types of NSHL**

Variety of protein coding genes such as gap junctions (connexin encoding genes), motor proteins (myosins) cytoskeletal (e.g. actin), ion channels, structural proteins (Tectorin alpha, Otoancorin, Stereocilin, etc), transcription factors (POU3F4, POU4F3 and Eyes absent 4 or EYA4), and additionally microRNA genes are involved in HL [Willems, 2004; Mencia et al., 2009; Mahdieh et al., 2010a]. *GJB2* mutations are seen in 50% of autosomal recessive HL in the Caucasians [Kelsell et al., 1997; Tekin et al., 2001]. Some genes e.g. *GJB2* gene is expressed in a variety of organs of the body while others such as *OTOA*ncorin is only expressed in the inner ear.
