MAPT and early-onset autosomal dominant Alzheimer disease: ,15 As expected, we observed a significant difference in aggregate morphology, with the use of rTg4510 seeds (which are composed of P301L mutant tau) as compared to seeds from the sporadic Alzheimer’s disease cases, as can be seen in the photomicrographs (Fig. 4B) in which the rTg4510-initiated aggregates are both significantly larger (Fig. 4C, P < 0.0001) and significantly less circular (Fig. 4D, P < 0.0001).