Bulbar signs, Cardiac conduction abnormality, Cerebellar atrophy, Cerebral edema, Chorea, Coma, Decreased activity of mitochondrial complex I, Decreased activity of mitochondrial respiratory chain, Demyelinating peripheral neuropathy, Developmental regression, Diabetes mellitus, Dilated cardiomyopathy, Dyskinesia, Dysphagia, Dyspnea, Dystonia, Encephalopathy, Episodic respiratory distress, Episodic vomiting, Exercise intolerance, Failure to thrive, Feeding difficulties, Feeding difficulties in infancy, Fetal distress, Fever, Focal T2 hyperintense basal ganglia lesion, Focal T2 hyperintense brainstem lesion, Gait ataxia, Generalized hypotonia, Generalized myoclonic seizure, Global developmental delay, Growth delay, Hepatic failure, Hepatomegaly, Hyperalaninemia, Hyperreflexia, Hypertrophic cardiomyopathy, Hyperventilation, Hypoglycemia, Hyporeflexia, Hypothermia, Hypotonia, Increased CSF lactate, Increased circulating lactate concentration, Increased serum pyruvate, Infantile muscular hypotonia, Infantile spasms, Intrauterine growth retardation, Lactic acidosis, Lacticaciduria, Lethargy, Leukodystrophy, Leukoencephalopathy, Low plasma citrulline, Microcephaly, Mitochondrial myopathy, Multiple glomerular cysts, Muscle weakness, Nystagmus, Ophthalmoparesis, Optic atrophy, Optic disc pallor, Optic neuropathy, Paroxysmal involuntary eye movements, Pigmentary retinopathy, Poor head control, Progressive macrocephaly, Proximal tubulopathy, Ptosis, Ragged-red muscle fibers, Reduced eye contact, Respiratory insufficiency, Rod-cone dystrophy, Segmental peripheral demyelination/remyelination, Seizure, Sensorimotor neuropathy, Sensorineural hearing impairment, Severe global developmental delay, Skeletal muscle atrophy, Spasticity, Strabismus, Vomiting