As shown in Figure 4, densitometric analysis of PARylation revealed a significant increase in PARylation levels in elav-Gal4 > Aβ42 samples relative to control elav-Gal4/+ samples, similar to previous results obtained in mouse and human models, an observation that suggests that the activation of PARP-1 is an important early event in the pathogenesis of AD. This evidence concerns the gene PARP1 and Alzheimer disease.