Succinate dehydrogenase [ubiquinone] cytochrome b small subunit, mitochondrial (CybS), also known as succinate dehydrogenase complex subunit D (SDHD), is a protein that in humans is encoded by the SDHDgene.
SDHD, which stands for succinate dehydrogenase complex subunit D, is one of the two transmembrane subunits of the four-subunit succinate dehydrogenase protein complex that resides in the inner mitochondrial membrane. It also refers to the gene that codes for this protein. The other transmembrane subunit is SDHC. SDHD/SDHC are connected to the SDHB electron transfer subunit. SDHB in turn transfers electrons from the SDHA subunit to the SDHC/SDHD dimer.
Germline mutations in SDHD were first linked to hereditary paraganglioma in 2000. Since then, it has been shown that mutations in SDHB and to a lesser degree SDHC can cause paranglioma as well familial pheochromocytoma. Notably, the tumor spectrum is different for the different mutations. SDHB mutations often lead to metastatic disease that is extra-adrenal, while SDHD mutation related tumors are more typically benign, originating in the head and neck.
The exact mechanism for tumorigenesis is not determined, but it is suspected that malfunction of the SDH complex can cause a hypoxic response in the cell that leads to tumor formation. People living at higher altitudes (for example, the Andes mountains) are known to have an increased rate of benign paraganglioma, with the rate of disease increasing with the altitude of the population.
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