A rare mitochondrial substrate carrier disorder characterized by severe muscular hypotonia, seizures (with or without episodic apnea) beginning in the first year of life, and arrested psychomotor development (affecting mainly motor skills). Severe spasticity with hyperreflexia has also been reported. Global cerebral hypomyelination is a characteristic imaging feature of this disease. The disease is Monarch Disease Ontology id MONDO_0013056 (developmental and epileptic encephalopathy, 39). Also known as: AGC1 deficiency, DEE39, EIEE39, SLC25A12 early infantile epileptic encephalopathy, developmental and epileptic encephalopathy 39, early infantile epileptic encephalopathy caused by mutation in SLC25A12, epileptic encephalopathy with global cerebral demyelination, epileptic encephalopathy, early infantile, 39.