GBA1 and Parkinson disease: Levels of glucosylsphingosine (GlcSph), another substrate for GBA and GBA2, as well as levels of sphingosine (Sph) and sphinganine (SphA) were quantified in substantia nigra of PD patients and age-matched controls (n = 10 per condition and n = 5 per age group) using RP-HPLC.