Choreoathetosis, Delayed speech and language development, Depigmentation/hyperpigmentation of skin, Developmental regression, Developmental stagnation, Developmental stagnation at onset of seizures, Dyskinesia, Failure to thrive, Feeding difficulties, Feeding difficulties in infancy, Functional motor deficit, Gastrointestinal dysmotility, Gastrostomy tube feeding in infancy, Generalized hypotonia, Global brain atrophy, Global developmental delay, Hearing impairment, Hyperintensity of cerebral white matter on MRI, Hypermelanotic macule, Hyperpigmented/hypopigmented macules, Hyporeflexia of upper limbs, Hypotonia, Inability to walk, Incoordination, Increased circulating lactate concentration, Infantile muscular hypotonia, Intellectual disability, profound, Intellectual disability, severe, Irritability, Lower limb hyperreflexia, Macular hyperpigmented dermopathy, Microcephaly, Motor stereotypy, Multifocal epileptiform discharges, Myoclonic spasms, Myoclonus, Nystagmus, Optic atrophy, Paroxysmal choreoathetosis, Poor eye contact, Profound global developmental delay, Progressive neurologic deterioration, Seizure, Sensorineural hearing impairment, Slow decrease in visual acuity, Status epilepticus, Tetraparesis, Tremor, Visual loss, Vomiting