To address this possibility, and to extend to other pathogenic mitochondrial tRNA mutations associated with mitochondrial diseases (e.g., in mitochondrial tRNAVal [51]), the label-free assay would be preferable, because it can readily accommodate high concentrations of tRNA while maintaining the relative concentration of the aaRS low enough to detect aminoacylation. The gene discussed is AARS1; the disease is mitochondrial disease.