GAD1 and neoplasm: To further understand the mechanisms related to the aberrant regulation of metabolites in distinct metabolic pathways, the expression of four rate-limiting enzymes in sugar and lipid metabolism, namely, glycogen synthase kinase 3 beta (GSK3β) [25,26], the dimeric pyruvate kinase muscle isozyme 2 (PKM2) [27], carnitine palmitoyltransferase 1A (CPT1A) [28] and glutamate decarboxylase 1 (GAD1), was examined in the tumor and NC tissues.