DEGS1 and leukodystrophy, hypomyelinating, 18: Likewise, malfunction of Δ4-dihydroceramide desaturase 1 (DEGS1), which converts dihydroceramide (DhCer) into Cer (8) at the last step of this de novo pathway, causes severe hypomyelinating leukodystrophy-18 (HLD18) (OMIM #618404) (9, 10, 11).