We found that multiple genes encoding enzymes in the γ-glutamyl cycle were highly downregulated in renal cysts, including γ-glutamyl transferase (GGT1, −14×), dipeptidase 1 (DPEP1, −32.5×), aminopeptidase N (ANPEP, −12×) and 5-oxoprolinase (OPLAH, −2.6×). This evidence concerns the gene GGT1 and cystic kidney disease.