TPH2 and epilepsy: The TPH2 labelling index in the VLM was significantly lower in SUDEP and definite SUDEP groups than non-epilepsy control groups (both non-epilepsy controls and non-epilepsy sudden death controls) (P < 0.005); no significant differences were noted between Dravet syndrome and epilepsy controls compared to non-epilepsy control groups (Table 4 and Fig. 3D).