In this regard, the gamma-glutamyltranspeptidase 1 and 5 (GGT1, GGT5), and the betaine homocysteine S-methyltransferase (BHMT), contributing to intracellular GSH and homocysteine maintenance were significantly down-regulated in renal oncocytomas, indicating a degradation brake in the gamma-glutamyl cycle, which might be the molecular reason for the high GSH levels. Here, GGT1 is linked to kidney oncocytoma.