Cluster 1 PPGLs include pheochromocytomas and abdominal paragangliomas carrying the highest risk of metastatic spread, especially the TCA cycle aberrant tumors carrying genetic variants in enzymes regulating the TCA cycle, including SDHA, SDHB, SDHAF2, FH, MDH2, ISH1 and SLC25A11 [73]. The gene discussed is MDH2; the disease is pheochromocytoma.