CBS and Dravet syndrome: The expression of CBS in various DS tissues exhibits cell-type selectivity: for example, in the DS brain, the higher expression of CBS is primarily localized to the astrocytes, as opposed to the neurons [13,24,27], and in adult human DS brains which also develop Alzheimer's type pathologies, CBS tends to concentrate in areas surrounding senile plaques and neurofibrillary tangles (Fig. 6) [13].