TLCD3B and myeloid sarcoma: Moreover, genes that are essential for de novo sphingolipid synthesis including serine palmitoyltransferases (SPTLC1/2/3) and ceramide synthases (CERS1/2/3/4/5) were down-regulated in OLs and OPCs of SPMS as compared to RRMS, indicating dysfunctions in myelin synthesis with MS progression.