SPTLC2 and Parkinson disease: Two subunits of serine palmitoyl transferase were down-regulated in IPD but either found at control levels (SPTLC1) or elevated in PD-GBA versus IPD (SPTLC1 and SPTLC2) (Table 1 and Fig. 7a); changes in SPTLC2 were validated by targeted proteomics (Supplementary Fig. 10A).