Bilateral Nonsyndromic Sensorineural Hearing Loss Caused by a NARS2 Mutation.

Mitochondrial diseases disrupt the process of energy generation by the mitochondria, leading to manifestations that can affect almost any organ in the body. Although various possible clinical phenotypes can result, neurological and neuromuscular affection is most frequently encountered. NARS2 encodes an enzyme responsible for the conjugation of asparagine to its cognate mitochondrial transfer ribonucleic acid (tRNA) molecule, representing an essential step necessary for effective mitochondrial protein synthesis. As such, mutations in this gene can lead to poor mitochondrial gene expression and, consequently, poor energy output resulting in disease. Pathogenic variants in NARS2 have been known to cause neurodegenerative and myopathic syndromes in combined oxidative phosphorylation deficiency 24 (COXPD24). However, nonsyndromic autosomal recessive deafness 94 (DFNB94), with which only one family is known to be affected, has also been reported concerning NARS2. Our report demonstrates the association of a new pathogenic variant in mitochondrial asparaginyl-tRNA synthetase (NARS2) with nonsyndromic sensorineural hearing loss, thus confirming biallelic mutations in NARS2 as a cause of nonsyndromic deafness.