Fig. 1.

Scheme showing the pathways for the synthesis of the major gangliosides. The genes encoding three critical enzymes are shown in red and represent GM2/GD2 synthase (Galgt1), GM3 synthase (Siat9), and GD3 synthase (Siat8a). The products not synthesized when Galgt1 is inactivated are shown by the hatch marks sloping down to the left, and those not synthesized when Siat9 is inactivated are shown by the hatch marks sloping down to the right. When both genes are inactivated, only the few glycolipids shown in the unhatched area are synthesized. The abbreviations represent ceramide (Cer), N-acetylgalactosamine (GalNAc), and N-acetylneuraminic acid (NeuAc). This diagram was developed by Dr. Richard Proia and was redrawn and modified slightly from reference (19) with permission of the authors and journal.