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, Kyphosis, Lactic acidosis, Lethargy, Leukodystrophy, Leukoencephalopathy, Macrovesicular hepatic steatosis, Metabolic acidosis, Microcephaly, Mitochondrial myopathy, Muscle weakness, Myopathy, Nystagmus, Optic disc pallor, Optic neuropathy, Osteoporosis, Paroxysmal involuntary eye movements, Poor eye contact, Poor head control, Progressive macrocephaly, Proximal tubulopathy, Ptosis, Respiratory insufficiency, Retinopathy, Scoliosis, Seizure, Sensorineural hearing impairment, Skeletal muscle atrophy, Spasticity, Strabismus, Vomiting