The rs267606619 T allele (also known as the 1494T allele) is assigned as a MT-RNR1 increased risk of aminoglycoside-induced hearing loss allele by CPIC. Patients with the T allele may have an increased risk of experiencing hearing loss when treated with tobramycin as compared to patients with the 1494C allele. Almost all individuals studied were homoplasmic for the T allele; it is unclear how heteroplasmy affects the severity or occurrence of aminoglycoside-induced hearing loss. MT-RNR1 is a mitochondrial gene and is inherited as a haploid (i.e. there is only ever one allele present). Other genetic and clinical factors may also influence risk of hearing loss when treated with tobramycin.