Taking into account the former considerations, namely, a) that genetics indisputably influences MS risk in a complicated manner, b) that CD33 may be implicated in some cardinal pathways of microglia and macrophage functions (mainly) and thus possibly in MS, c) that a CD33 variant has been associated with NMOSD, and d) that the CD33 rs3865444 is a promoter variant that appears to modify CD33 function and has been associated with AD, we aimed to examine the possible crude association of rs3865444 with MS by performing a case-control study. This evidence concerns the gene CD33 and myeloid sarcoma.