Decreased activity of mitochondrial complex I, Decreased activity of mitochondrial respiratory chain, Developmental regression, Diabetes mellitus, Dyskinesia, Encephalopathy, Exercise intolerance, Failure to thrive, Feeding difficulties, Feeding difficulties in infancy, Fetal distress, Focal T2 hyperintense brainstem lesion, Generalized hypotonia, Global developmental delay, Growth delay, Hepatic failure, Hepatomegaly, Hyperreflexia, Hypertrophic cardiomyopathy, Hypoglycemia, Hyporeflexia, Hypotonia, Increased CSF lactate, Increased circulating lactate concentration, Increased serum pyruvate, Intrauterine growth retardation, Lactic acidosis, Lethargy, Leukodystrophy, Leukoencephalopathy, Microcephaly, Mitochondrial myopathy, Muscle weakness, Myopathy, Nystagmus, Optic atrophy, Optic disc pallor, Optic neuropathy, Paroxysmal involuntary eye movements, Poor eye contact, Poor head control, Progressive macrocephaly, Proximal tubulopathy, Ptosis, Respiratory insufficiency, Secondary microcephaly, Seizure, Sensorineural hearing impairment, Skeletal muscle atrophy, Spasticity, Strabismus, Vomiting