Among these, we preferably considered the mutations in subjects presenting audiograms compatible to a mitochondrial mutation HL diagnosis, in conserved positions and with a frequency <0.05%, such as: i) the mutation A>G in the conserved position 644 (0,04% in mtDB) in MT-TF, located in the acceptor stem of tRNAPhe. 644A>G found in a 13-year-old girl with SNHL, harbouring the polymorphisms, G709A, G1888A and C7873T; ii) T721C in MT-RNR1. This evidence concerns the gene NR4A2 and sensorineural hearing loss disorder.