In contrast, cathepsin D levels were significantly elevated in Grn−/− mouse brains [38,39,40], in the microglia of Grn KO mice [41], and also in frontal cortex of both FTLD-TDP patients with the GRN mutation and NCL patients [39], suggesting a possible compensatory mechanism in response to the loss of progranulin. The gene discussed is GRN; the disease is neuronal ceroid lipofuscinosis.