MT-RNR1 and hearing loss disorder: As an example, we discovered in our clinical center the m.1555G>A variant in the MT-RNR1, responsible for the amino-glycoside-induced and non-syndromic hearing loss (Bitner-Glindzicz et al., 2009; Vandebona et al., 2009) in a family with isolated optic atrophy but without hearing impairment.