NDUFS4 and mitochondrial disease: In order to develop a suitable vector for gene therapy in Leigh disease, a multisystem mitochondrial disease, we cloned the human wild-type NDUFS4 cDNA (hNDUFS4) into a single-stranded AAV2/9 viral vector under the control of the strong, general promoter of the cytomegalovirus (CMV) (AAV2/9-hNDUFS4) (Figure 1a).