GBA1 and Parkinson disease: Our finding of increased expression of GBA mRNA in the PD substantia nigra was surprising as others have reported decreased GBA gene expression in the substantia nigra in patients with sporadic PD (Chiasserini et al., 2015) and reduced GBA gene expression in brain regions with and without pathological synuclein aggregates and in early and late-stage sporadic PD (Murphy et al., 2014).