CBS and Dravet syndrome: Most recently, using the Dp(17)3Yey/+ mice — another model of DS, which contains an extra copy of CBS, and several other genes encoded on mouse chromosome 17, but does not contain an extra copy of many other genes encoded on human chromosome 21 [48] — we higher H2S production rates were detected in the brain homogenates of DS mice than in control wild-type mice; this was associated with slightly elevated plasma (by 22 ​%) and brain (by 26 ​%) free H2S levels [27].