The triple comparison shown in the Venn diagram (Figure 2A), surprisingly identified the Spp1 gene as the only one that appeared to be differentially expressed when comparing, by pairs, the gene expression levels of AQP4−/− mice with obstructive hydrocephalus (OH) or without hydrocephalus (NH), and wild-type animals (WT). Here, AQP4 is linked to obstructive hydrocephalus.