In this context, the glutamate balance via the glutamate–glutamine (Glu–Gln) shuttle is critical for cognitive functions and excitotoxicity in AD being glutamine synthetase (GS) a key element in the Glu–Gln cycle without forgetting the (Glu–Gln-GABA metabolism cycle) fundamental for both excitatory and inhibitory transmission (Eid et al. 2012). The gene discussed is GLUL; the disease is Alzheimer disease.