SMPD1 and diabetes mellitus: Dysfunctional sphingolipid metabolism in the diabetic retina, with an increase in SC ceramides due to pathological activation of ASM and a decrease in VLC ceramides due to downregulation of ELOVL4-mediated production of VLC saturated fatty acids, is an important metabolic insult contributing to the development of DR (50, 51, 52, 106, 107).