CBS and Dravet syndrome: With respect to circulating thiosulfate levels in DS, at least two factors may be involved: (a) the action of TST, which primarily synthesizes, rather than consumes thiosulfate [53]: in DS, since TST activity is reduced, a reduction in thiosulfate levels would be expected and (b) the increased expression of CBS and the increased production of H2S [14], which would be expected to increase thiosulfate levels.