PRNP and scrapie: Interestingly, position 169 lies in the loop connecting the second β sheet and the second α helix (β2-α2) (Fig. 7), a region which is critical in conditioning the PrPC three-dimensional structure [25], the formation of fibrils [26], the susceptibility of sheep to scrapie [27]–[29], the replication of prions [30] and the transmission barrier ([11],[19], present paper).