As the only known enzyme that catalyzes the synthesis of endogenous Gln from glutamate and ammonia in an adenosine triphosphate (ATP)-dependent pathway, glutamine synthetase (GS) has been reported to be generally overexpressed in breast, prostate and pancreatic cancers, where it maintains the proliferation and survival of cancer cells when the source of Gln is limited (Listrom et al., 1997; Pissimissis et al., 2009; Kung et al., 2011; Yuneva et al., 2012; Shi et al., 2014; Bott et al., 2015). The gene discussed is GLUL; the disease is cancer.