Second, in investigating the cellular machinery responsible for proliferation and apoptosis, evidence was found that was consistent with the effects on the cell cycle being mediated by hyperphoshorylation of Rb in DS tumors and that the effect on apoptosis was mediated, at least in part, by interference with the activity of executioner caspases via inhibitor of apoptosis proteins such as XIAP (Figure 3). This evidence concerns the gene RB1 and Dravet syndrome.