Basic chemical structure of glycosphingolipids. a. Glycosphingolipids are composed of a sphingosine, a fatty acid chain (these two forming a ceramide) and a carbohydrate moiety (X). The fatty acid attached to the sphingosine may vary in chain length and in degree of unsaturation and/or hydroxylation. b. Example of glycosphingolipids and their corresponding carbohydrate moiety. A sphingolipid with a X group consisting of a hydrogen atom only is a ceramide. Glc: glucose; Gal: galactose; NeuNAc: N-acetylneuraminic acid (i.e. sialic acid). GA stands for asialo-, GM for monosialo-, GD for disialo-, GT for trisialo-, GQ- for quadrisialo- and GP for pentasialo-ganglioside.