Sphingosines are long-chain base precursors of cellular sphingolipids used directly in the synthesis of ceramide, which in combination with sialic acid forms ganglioside. Sphingosine can exist in four stereoisomers, however only sphingosine occurs naturally. Compared to other sphingolipids throughout the body, which are predominantly composed of C-18 sphingosine, only central nervous system (CNS) gangliosides contain significant amounts of sphingosine. The concentration of sphingosine within mammalian brain gangliosides apparently increases with developmental maturation. Furthermore, the ratio of C-18 to C-20 sphingosine in the brain is thought to be related to some nervous system degeneration processes.