Another study using iPSC‐derived dopamine neurons from PD patients carrying homozygous GBA1 mutations (N370S/N370S and N370S/c0.84dupG) and GD patients with N370S/N370S and IVS2+1G>T/L444P genotypes showed that the presence of the severe homozygous GBA1 mutations leads to significant accumulation of α‐synuclein protein compared to cells with homozygous mild GBA1 mutations in iPSC‐derived dopaminergic neurons (Aflaki et al., 2016). Here, GBA1 is linked to Parkinson disease.