Recent advances in the genetics of SDH-related paraganglioma and pheochromocytoma

The last 10 years have seen enormous progress in the field of paraganglioma and pheochromocytoma genetics. The identification of the first gene related to paraganglioma, SDHD, encoding a subunit of mitochondrial succinate dehydrogenase (SDH), was quickly followed by the identification of mutations in SDHC and SDHB. Very recently several new SDH-related genes have been discovered. The SDHAF2 gene encodes an SDH co-factor related to the function of the SDHA subunit, and is currently exclusively associated with head and neck paragangliomas. SDHA itself has now also been identified as a paraganglioma gene, with the recent identification of the first mutation in a patient with extra-adrenal paraganglioma. Another SDH-related co-factor, SDHAF1, is not currently known to be a tumor suppressor, but may shed some light on the mechanisms of tumorigenesis. An entirely novel gene associated with adrenal pheochromocytoma, TMEM127, suggests that other new paraganglioma susceptibility genes may await discovery. In addition to these recent discoveries, new techniques related to mutation analysis, including genetic analysis algorithms, SDHB immunohistochemistry, and deletion analysis by MLPA have improved the efficiency and accuracy of genetic analysis. However, many intriguing questions remain, such as the striking differences in the clinical phenotype of genes that encode proteins with an apparently very close functional relationship, and the lack of expression of SDHD and SDHAF2 mutations when inherited via the maternal line. Little is still known of the origins and causes of truly sporadic tumors, and the role of oxygen in the relationships between high-altitude, familial and truly sporadic paragangliomas remains to be elucidated

Mutation of SDHB is a Cause of Hypoxia-Related High-Altitude Paraganglioma

Purpose: Paragangliomas of the head and neck are neuroendocrine tumors and are associated with germ line mutations of the tricarboxylic acid cycle-related genes SDHB, SDHC, SDHD, and SDHAF2. Hypoxia is important in most solid tumors, and was directly implicated in tumorigenesis over 40 years ago when it was shown that dwelling at high altitudes increases the incidence of carotid body hyperplasia and paragangliomas. Although recent research has now elucidated several pathways of hypoxia in paragangliomas, nothing is currently known of the genetics or of gene-environment interactions in high-altitude paraganglioma. We postulated that SDH mutations might play a role in these tumors. Experimental Design: Patients from a Mexican family, originating and resident in Guadalajara, were tested for mutations of SDHD, and subsequently, for mutations of SDHB followed by immunohistochemical confirmation of SDHB loss. Results: Two patients, born and resident at altitudes of between 1,560 and 2,240 m, were found to have head and neck paragangliomas, including a remarkably aggressive recurrent tumor. Mutation analysis identified a pathogenic missense mutation in exon 7 of SDHB, c. 689G>A, p.Arg230His, and loss of the SDHB protein was confirmed by immunohistochemistry. Conclusions: This is the first report of a SDH gene mutation in paraganglioma at high altitude. A rapidly recurrent head and neck paraganglioma is a very rare finding in an SDH mutation carrier, suggesting a gene-environment interaction. Neither patient showed evidence of sympathetic paraganglioma. Clin Cancer Res; 16(16); 4148-54. (C) 2010 AACR