The drop of 5hmC in DS samples is mainly associated with the down-regulation of TET1. Moreover, we show hypermethylation of few CpGs at TET1 promoter in DS samples when compared with age-matched controls, but this slight increase in 5mC is unlikely to explain by itself the silencing of TET1. Notably, we observed no difference with the methylation profile of a group of elderly population enrolled in the context of the same project (14). This evidence concerns the gene TET1 and Dravet syndrome.