 Cystinosis is a rare genetic disorder caused by a mutation in the gene coding for cystinosin, CTNS. This mutation leads to the build-up of cystin in the lysosomes of affected cells, resulting in impaired function and death of these cells. In this study, researchers found that the presence of cystin in lysosomes activates the MTORC1 pathway, leading to increased cell growth and proliferation. They also discovered that introducing CTNS into cells lacking it can restore normal cellular function. Furthermore, they developed a drug that blocks the activity of MTORC1 and successfully treated cystinosis in mouse models. This article was authored by Marine Berkers, Jiang Chen, Beatrice Palifesta and others.