CBS and cancer: In light of the implication of CBS in the cognitive phenotype of DS [12,13,14] and in cancer [9,10,11], several groups have sought in the last few years to identify inhibitors of CBS using in vitro screening methods, which, unfortunately, only identified compounds with relatively low potency and limited selectivity [15,16,17,18,19], suggesting that in vitro screening based on the recombinant protein is not an efficient approach to identify CBS inhibitors.