Mutations in the nuclear gene coding for the mitochondrial aspartyl-tRNA synthetase, a key enzyme for mitochondrial translation, are correlated with leukoencephalopathy. A Ser⁴⁵ to Gly⁴⁵ mutation is located in the predicted targeting signal of the protein. We demonstrate in the present study, by in vivo and in vitro approaches, that this pathology-related mutation impairs the import process across mitochondrial membranes.