Upon thorough review of the clinical history and inspection of copies of detected mtDNA variants, hearing loss in a patient (YUHL58-21) carrying the homoplasmic m.7444G>A mutation in MT-CO1, and in three patients (YUHL390-21, YUHL681-21 and YUHL847-21) harboring the homoplasmic m.1555A>G mutation in MT-RNR1, was determined to be associated with mtDNA variants (Fig. 4b, c). This evidence concerns the gene NR4A2 and hearing loss disorder.