CBS and Dravet syndrome: Over the subsequent 30 years, several studies have confirmed and extended these observations, and demonstrated that human DS cells and tissues (Fig. 6a) [13] and tissues of DS rodents contain elevated levels of CBS mRNA, increased expression of CBS protein, and/or increased CBS enzymatic activity (Table 1) [13,18,23,24,27,29,[51], [52], [53], [54], [55], [56], [57], [58], [59], [60], [61], [62], [63], [64], [65], [66], [67], [68], [69]].