ABSTRACT
Mitochondria are one of the most important organelles of the cell. It plays an important role in cell function providing energy and also in cell death (apoptosis). The human inner ear contains nervous tissue and it has a very high metabolism rate, especially in the vascularis stria. It is an organ with high sensitivity to damage because of its lower energy. The function of the cochlea is to convert the sound waves into an electrochemical stimulus, which can be transmitted to the Central Nervous System (CNS). The receptor of this sensory function are the inner hair cells (IHC) in which stereocilial movement produces ion channels opening to allow the entry of K+ and Ca++. This result in a transduction current which generates the activation the calcium channels that is in the wall and the base of the IHC. The hearing loss (HL), secondary to mitochondrial dysfunction, is of two types, Non-syndromic HL and Syndromic HL. In the first type, the patients suffer from isolated HL, some of them after aminoglycosides exposure HL. There are pathogenic variants in various genes involved, such as MT-RNR1 and MT-TS1. There are 2 other HL non-syndromic that are important because of their frequency, the Noise Induced Hearing Loss and Presbycusis; These diseases can be caused by mitochondrial dysfunction without specific mutations and the accumulation of different mitochondrial mutations due to the lifespan of people. In the group of syndromic HL there are different phenotypes, but the great majority affecting the CNS. In this group there are well defined syndromes as Kearns-Sayre, MELAS, MERRF, Keratoderma palmoplantar with deafness, MERRF/MELAS overlap, MIDD (Maternal inherited diabetes and deafness) and Mitochondrial Cytochrome c Oxidase Deficiency syndromes. Many genes with different mutations are involved as a cause of these syndromes, the most frequent are: MT-TL1 and MT-TS1. Other genes described are: MT-Tk, MT-TH, MT-TS2 and MT-NDA5. It is important to look for mitochondrial mutations in patients with severe neurological disturbances including HL and ophthalmological problems.
