Heatmap of HIF1α target genes. Samples are represented as columns and genes as rows. Samples are ordered from left to right: PGL2-linked paragangliomas (yellow), SDHD-linked paragangliomas (blue), and sporadic paragangliomas (grey). In all, 264 pathways and functional gene sets related to processes that are assumed to play a role in paraganglioma formation (i.e. proliferation, survival, apoptosis, cell cycle regulation, metabolism and hypoxia) were tested (data not shown). None of them showed significant differential gene expression between SDHD-linked, PGL2-linked and sporadic paragangliomas, including the gene sets encoding SDH and HIF1α target genes involved in the processes of angiogenesis, glucose metabolism and proliferation.