Paraganglioma syndrome includes inherited head and neck paragangliomas (HNPs) and adrenal or extra-adrenal pheochromocytomas and are classified according to the susceptibility genes SDHB, SDHC, and SDHD.
In multiple endocrine neoplasia (MEN) 2a, the expression of the SDH genes and VHL mRNA was significantly higher than that observed in adrenal or extra-adrenal pheochromocytoma.
While SDHD has been more frequently associated with the pathogenesis of head and neck paragangliomas, SDHB mutations were mainly associated with malignant and/or extra-adrenal pheochromocytoma/paraganglioma.
Recent studies have demonstrated that SDH gene mutations in germ line occur in at least 11% of non-familial head and neck paragangliomas, 8% of non-familial pheochromocytomas, 28% of malignant pheochromocytomas and 33% of extra-adrenal pheochromocytomas.