These results provide a correlation of kidney-targeted gene inactivation with renal carcinoma, and they suggest that the BHD product FLCN, functioning as a cyst and tumor suppressor, like other hamartoma syndrome–related proteins such as PTEN, LKB1, and TSC1/2, is a component of the mTOR pathway, constituting a novel FLCN-mTOR signaling branch that regulates cell growth/proliferation. Here, FLCN is linked to cyst.