However, by day 40, GBA1-PD neurons exhibited a lower population of TUJ1-positive neurons (Fig. 2A, 71.9 ± 4.8 % and 56.2 ± 5.7 %, for control and GBA1-PD neurons, respectively), similar to a reduction of neurite length in GBA1-PD neurons (Figs. 2B and 1385.1 ± 305 μm and 1077.8 ± 363 μm for control and GBA1-PD neurons, respectively). Here, GBA1 is linked to Parkinson disease.