GSTM1 and noise induced hearing loss: In addition to contradictory results in various studies, the effect of genetic factors on susceptibility of NIHL can only be regarded as valid when they have been replicated in an independent population [17]; so, the present study investigates the association between the deletion polymorphism in the GSTT1 (rs1049055) and GSTM1 (rs10712361) genes and susceptibility to NIHL in Iranian population.