GBA1 and Parkinson disease: Since the pioneering report linking GD and PD, a plethora of studies have been undertaken to comprehend the role of GCase and its substrates—specifically Glycosphingolipids (GSLs), such as glucosylceramide (GlcCer) and glucosylsphingosine (GlcSph)—in the pathogenesis of GBA1-PD.