STX6 and prion disease: For each of the 10–5, 10–6, 10–7, and 10–8 concentrations, the proportion of prion disease cases relative to the animals surviving to the end of the study (attack rate, see methods) was consistently lower in Stx6−/− mice relative to Stx6+/+ mice, suggesting that they were more resistant to disease development (Table 1; Fig. 4).