CTSD and Gaucher disease: On western blotting, cathepsin D was significantly increased in Gaucher disease [median 50% increase (IQR 32–100%), Mann-Whitney U-test P < 0.0001] and Parkinson’s disease with GBA mutation [median 30% increase (IQR 20–40%), P = 0.002] fibroblasts (Fig. 4D).