NDUFS4 and inborn mitochondrial metabolism disorder: To determine whether VA exposure leads to toxic sequelae in the setting of ETC CI mitochondrial disease, we established an experimental paradigm whereby Ndufs4(−/−) animals were exposed to isoflurane 0.2%, 0.4%, or 0.6% in oxygen 100% (O2 100%); O2 100% (carrier gas) only; or air (mock exposure) for 30 min once per day for 3 days starting at P50 (Fig. 1a), while control animals were exposed to an equimolar (0.4%) or equipotent (anaesthetising) 1.25% concentration for comparison.