Mitochondrial aspartate-glutamate carrier isoform 1 (AGC1) deficiency (DEE39; OMIM #612949; ICD-10 Code: G31.8; ORPHA Nr: ORPHA353217) is an ultra-rare (less than 10 cases known worldwide) developmental and epileptic encephalopathy caused by mutations in SLC25A12 gene encoding the AGC1, a member of the SLC25 family of transport proteins of the inner mitochondrial membrane. The gene discussed is SLC25A12; the disease is developmental and epileptic encephalopathy.