Claudins are the pivotal transmembrane proteins in TJs (tight junctions), and their expression are often reduced and play important roles in ccRCC, including CLDN8 (claudin-8) 11, CLDN7 (claudin-7) 12, and CLDN2 (claudin-2) 13. The gene discussed is CLDN2; the disease is nonpapillary renal cell carcinoma.