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