Leukoencephalopathy-thalamus and brainstem anomalies-high lactate (LTBL) syndrome is a rare, genetic neurological disorder defined by early-onset of neurologic symptoms, biphasic clinical course, unique MRI features (incl. extensive, symmetrical, deep white matter abnormalities), and increased lactate in body fluids. The severe form is characterized by delayed psychomotor development, seizures, early-onset hypotonia, and persistently increased lactate levels. The mild form usually presents with irritability, psychomotor regression after six months of age, and temporary high lactate levels, with overall clinical improvement from the second year onward. The disease is leukoencephalopathy-thalamus and brainstem anomalies-high lactate syndrome (Monarch Disease Ontology term MONDO_0013971). Also known as: COXPD12, EARS2 combined oxidative phosphorylation deficiency, LTBL, combined oxidative phosphorylation defect type 12, combined oxidative phosphorylation deficiency caused by mutation in EARS2, combined oxidative phosphorylation deficiency type 12.