NDUFS1 and mitochondrial complex I deficiency, nuclear type 5: MCID nuclear type 5 (MC1DN5) is caused by rare mutations in the NADH dehydrogenase Fe-S protein 1-coding NDUFS1 gene.[17] The onset of symptoms in patients with MCIDN5 is usually in infancy, like in our patient, who was symptomatic and showed signs of mitochondrial dysfunction, brain imaging abnormalities, elevated blood and CSF lactic acid, and defective MRC complex enzyme I activity.