In a phase 2, open-label study (NCT02941822) involving 17 PD patients with and without GBA mutations, ambroxol (at an escalating oral dose to 1.26 g per day) was able to both cross the blood–brain barrier (BBB) and to increase the GCase and α-synuclein concentrations in the cerebrospinal fluid (CSF) [38]. Here, GBA1 is linked to Parkinson disease.