CTSB and Alzheimer disease: This non-specific activity was then subtracted from the total activity to identify the proportion of the activity specific to cathepsin B. Using this method, we observed that cathepsin B activity is elevated in the temporal cortex of people who had EOAD compared with healthy controls, but that no difference in cathepsin B activity was observed in individuals who have AD-DS compared to healthy ageing controls (Fig. 1h).