NDUFS2 and Menkes disease: As shown in Fig. 2A, three fibroblast cell lines from healthy volunteers (C5120, C5119, and C5118) and three fibroblast cell lines from mitochondrial Complex I deficient (MD) patients [S7-5175 (NdufS7, V112M mutation), S2-7277 (NdufS2, R228Q mutation), and V1-5171 (NdufV1, R59X/T423M mutation)] were exposed for 24 h to 1 μM KH176m or vehicle, after which the cells were processed for metabolomics analysis.