CTSD and Gaucher disease: After ambroxol treatment cathepsin D levels fell in Gaucher disease [median fall 30% (IQR 25–50%), P = 0.03] and Parkinson’s disease with GBA mutation cells [median fall 20% (IQR 15–40%), P = 0.04] (Fig. 5), as did total beta-hexosaminidase activity [Gaucher disease median fall 36.5% (IQR 26.2–50%), P = 0.012 and Parkinson’s disease with GBA mutation median fall 30% (IQR 20–50%), P = 0.019].