Novel Cases of Non-Syndromic Hearing Impairment Caused by Pathogenic Variants in Genes Encoding Mitochondrial Aminoacyl-tRNA Synthetases

Dysfunction of some mitochondrial aminoacyl-tRNA synthetases (encoded by the KARS1,
HARS2, LARS2 and NARS2 genes) results in a great variety of phenotypes ranging from nonsyndromic hearing impairment (NSHI) to very complex syndromes, with a predominance of neurological signs. The diversity of roles that are played by these moonlighting enzymes and the fact
that most pathogenic variants are missense and affect different domains of these proteins in diverse
compound heterozygous combinations make it difficult to establish genotype–phenotype correlations.
We used a targeted gene-sequencing panel to investigate the presence of pathogenic variants in those
four genes in cohorts of 175 Spanish and 18 Colombian familial cases with non-DFNB1 autosomal
recessive NSHI. Disease-associated variants were found in five cases. Five mutations were novel
as follows: c.766C>T in KARS1, c.475C>T, c.728A>C and c.1012G>A in HARS2, and c.795A>G in
LARS2. We provide audiograms from patients at different ages to document the evolution of the
hearing loss, which is mostly prelingual and progresses from moderate/severe to profound, the
middle frequencies being more severely affected. No additional clinical sign was observed in any
affected subject. Our results confirm the involvement of KARS1 in DFNB89 NSHI, for which until
now there was limited evidence.