RET and von Hippel-Lindau disease: PPGLs are tumors with a high genetic heterogeneity; susceptibility genes include “old genes” associated with Neurofibromatosis type 1 (NF1 gene), Von Hippel Lindau syndrome (VHL gene), and Multiple Endocrine Neoplasia type 2 syndrome (RET gene), the genes of the succinate dehydrogenase complex (SDHx genes: SDHA, SDHB, SDHC, SDHD, SDHAF2), and the more recently discovered genes TMEM, MAX, and FH.