SPHK1 and Alzheimer disease: In our previous study, we observed age- and AβPP (V717I)-related reduction of SPHK2, CERK, and S1PRs mRNAs, which largely mirrored the changes observed in human hippocampal post-mortem AD material (lower SPHK1 and SPHK2, S1PR1, and CERK) [27].