Mitochondrial glutamate carriers 1 and 2 (SLC25A22, GC1, and SLC25A18, GC2) belong to the mitochondrial carrier family of transport proteins that shuttle substrates, metabolites, and cofactors through the mitochondrial membrane, connecting the cytosol to the mitochondrial matrix. Glutamate (Glu) can be co-transported with H+ via SLC25A18 and SLC25A22, located on the inner mitochondrial membrane (Fiermonte et al., 2002). Defects in SLC25A22 can cause early infantile epileptic encephalopathy 3 (EIEE3; MIM:609304), a severe neonatal epilepsy characterized by very early onset, erratic and fragmentary myoclonus. With no treatment available, children with EIEE3 die within 1 or 2 years of birth or survive in a vegetative state (Molinari et al., 2005; reviewed in Spoto et al., 2021).