Fig. 3

Principal component analysis of PD studies based on differential expression signatures. PCA of the 1,008 genes in the union of the top 50 genes by absolute log-fold change across all 33 studies reveals a distinct group of studies composed mainly of human studies (centre, right) of the substantia nigra and frontal cortex (left). There appears to be little separation between different disease model types (right); although the two studies using other neurotoxins (rotenone and Maneb-Paraquat) appear very distinct from the other studies. This is most clearly visualised in the second and third principal components; a similar separation is seen in the first two principal components (see Additional file 5)