“…When nucleation is a rare event, the emergence of measurable amounts of protein aggregates is preceded by a lag phase whose variable duration reflects the probability distribution of a successful event (Crespo et al, 2012;Michaels et al, 2016). During amyloid fibril formation, prior addition of > 1% of preformed fibrils (or seeds) is often sufficient to eliminate the lag phase and the intrinsic uncertainty associated to primary nucleation (Sárkány et al, 2019). Conversely, protein samples containing residual, yet variable, amounts of preformed seeds may not be suitable for "unseeded" assays due to irreproducible lag times (Crespo et al, 2012(Crespo et al, , 2016.…”