Novel Germline SUCLG2 Mutations in Patients With Pheochromocytoma and Paraganglioma

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors derived from neural crest cells that are frequently linked to mutations including those in Krebs cycle enzymes, particularly succinate dehydrogenase (SDH). Succinyl-CoA ligase (SUCL) catalyzes reversible conversion of succinyl-CoA to succinate providing the substrate for SDH. While mitochondrial diseases were documented for the mutations in SUCL subunits G1 and A2, the association of GDP/GTP-specific subunit SUCLG2 mutations with specific pathologies including cancer have not been reported. In our study, 352 patients with apparently sporadic PPGLs underwent genetic testing using a panel of 54 genes developed at the National Institutes of Health. Additionally, human pheochromocytoma (hPheo1) cells were used for gene manipulation to produce SUCLG2 knock-out (KO). Tumor tissues and hPheo1 SUCLG2 KO cells were used for further analysis focusing on mechanism of germline variants effect on mitochondrial functions. We detected eight germline SUCLG2 mutations in 15 patients which represents 4.3% of the cohort. Germline variants together with LOH led to decreased levels of SDH subunit B resulting in aberrant respiration and accumulation of succinate, well recognized oncometabolite. Manipulation of SUCLG2 in hPheo1 cells confirmed decrease in SDHB leading to faulty assembly of mitochondrial complex II and alteration of its respiration and activity. In summary, our study identified an association between SUCLG2 and PPGL. Larger scale sequencing and uncovering additional cases bearing SUCLG2 variants will further clarify the relationship between SUCLG2 and SDHx, particularly SDHB, as well as their role in disease etiology.