GBA1 and Parkinson disease: Importantly, the pathology of PD‐GBA1 is identical to idiopathic PD, with nigral dopamine cell loss, Lewy bodies, and neurites containing α‐synuclein, so although the exact mechanism by which GBA1 mutations increase the risk for PD is still unknown, it is likely that as in idiopathic PD, accumulation of α‐synuclein, especially α‐synuclein phosphorylated at serine 129 (S129), plays an important role in the development and progression of PD‐GBA1.