DEGS2 and keratoconus: Moreover, since P is detected in KC incubated with NDS, generated DS from NDS is used for NDS synthesis, and then metabolized to NS and NP by desaturase/sphingoid ∆ (4) desaturase 1 (DEGS1) and sphingolipid C-4 hydroxylase/sphingolipid ∆ (4)-desaturase 2 (DEGS2), respectively (Figure 1).