Human Mitochondrial tRNA Mutations in Maternally Inherited Deafness

Mutations in mitochondrial tRNA genes have been shown to be associated with maternally inherited syndromic and non-syndromic deafness. Among those, mutations such as tRNALeu(UUR) 3243A>G associated with syndromic deafness are often present in heteroplasmy, and the non-syndromic deafness-associated tRNA mutations including tRNASer(UCN) 7445A>G are often in homoplasmy or in high levels of heteroplasmy. These tRNA mutations are the primary factors underlying the development of hearing loss. However, other tRNA mutations such as tRNAThr 15927G>A and tRNASer(UCN) 7444G>A are insufficient to produce a deafness phenotype, but always act in synergy with the primary mitochondrial DNA mutations, and can modulate their phenotypic manifestation. These tRNA mutations may alter the structure and function of the corresponding mitochondrial tRNAs and cause failures in tRNAs metabolism. Thereby, the impairment of mitochondrial protein synthesis and subsequent defects in respiration caused by these tRNA mutations, results in mitochondrial dysfunctions and eventually leads to the development of hearing loss. Here, we summarized the deafness-associated mitochondrial tRNA mutations and discussed the pathophysiology of these mitochondrial tRNA mutations, and we hope these data will provide a foundation for the early diagnosis, management, and treatment of maternally inherited deafness.