CBS and Dravet syndrome: It should also be emphasized that in some systems — e.g., in induced pluripotent stem cell systems [62,69] and when comparing various DS fibroblast lines [25] — the cell-line to cell-line (i.e. donor-to-donor) variability is rather high, perhaps reflecting individual differences in how various DS individuals' cells counterregulate and/or perhaps further amplify the gene dosage effect of the extra copy of cbs gene.