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International audience; Mutations in human mitochondrial aminoacyl-tRNA synthetases are associated with a variety of neurodegenerative disorders. The effects of these mutations on the structure and function of the enzymes remain to be established. Here, we investigate six mutants of the aspartyl-tRNA synthetase correlated with leukoencephalopathies. Our integrated strategy, combining an ensemble of biochemical and biophysical approaches, reveals that mutants are diversely affected with respect to their solubility in cellular extracts and stability in solution, but not in architecture. Mutations with mild effects on solubility occur in patients as allelic combinations whereas those with strong effects on solubility or on aminoacylation are necessarily associated with a partially functional allele. The fact that all mutations show individual molecular and cellular signatures and affect amino acids only conserved in mammals, points towards an alternative function besides aminoacylation. Mitochondria are the powerhouses of the eukaryotic cell, hosting the production of energy in the form of ATP by oxidative phosphorylation of ADP. They possess their own genome (mt-DNA), which codes in humans for 13 of the respiratory chain subunits, 22 tRNAs and 2 rRNAs. More than one thousand proteins, encoded by the nuclear genome, synthesized in the cytosol and subsequently imported into mitochondria, are also required for mitochondrial biogenesis and functioning (reviewed in e.g. 1). Defects in mt-DNA were correlated to human disorders more than 25 years ago 2. More recently, mitochondrial disorders were also associated with mutations within imported molecules, like factors of the mitochon-drial translation machinery 3–5. Among these are mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs), which catalyze the esterification of tRNAs with cognate amino acids, and are key actors of the synthesis of the 13 respiratory chain subunits. In 2007, it was shown for the first time that a mt-aaRS is implicated in a disease when mutations were found in the DARS2 gene coding for the mitochondrial aspartyl-tRNA synthetase (mt-AspRS) 6. This attracted the attention of the medical community and the steadily growing number of cases reported since then led to the current statement that all mt-aaRS genes (except WARS2) are affected by pathology-related mutations 1,7–12. Mt-aaRSs are impacted in various ways, despite being ubiquitously