[Thomas Weimbs] and his colleagues recently demonstrated that the gene regulates a signaling protein called mTOR that controls cell growth and proliferation. Scientists already knew that rapamycin inhibited mTOR, but they were not aware of the protein's role in cyst growth.

They then looked at humans who had received kidney transplants for the disease. Typically, surgeons leave the diseased kidneys in the body, adding the transplant as a third kidney. Rapamycin is often used in the transplant to prevent organ rejection.

The team found four patients who had received rapamycin and had CT scans of their kidneys immediately before or after the transplant and two years later. They observed that the diseased kidneys in the rapamycin recipients had shrunk by about 25% over the two-year period after surgery, while kidneys in those who received other anti- rejection drugs remained the same size.