A proportion of PCCs occurs in hereditary cancer syndromes, including multiple endocrine neoplasia Type 2 (MEN2), caused by mutations in the RET proto-oncogene, von Hippel-Lindau (VHL) disease, caused by VHL gene abnormalities, and the pheochromocytoma-paraganglioma (PCC-PGL) syndrome, caused by mutations in SDHB and SDHD.
The VHL gene product, pVHL, has multiple functions, but the best documented, and the one most clearly linked to tumor development, relates to its role as the substrate recognition module of a ubiquitin ligase complex that targets hypoxia-inducible factor (HIF) for destruction. pVHL function is often compromised in sporadic kidney cancers, and inhibitors of the HIF-responsive growth factor (vascular endothelial growth factor) are active against this disease. pVHL, by inhibiting atypical protein kinase C and hence JunB, also affects neuronal survival, as do the products of the other genes linked to familial pheochromocytoma or paraganglioma (NF1, RET, SDHB, SDHC, and SDHD).
A large body of evidence supports the absence of mutations in SDH, RET and VHL genes, which suggests the existence of a yet unknown gene at the origin of this particular form of familial PGL.
Analysis of paraganglioma tissue revealed loss of the VHL wild-type allele in both tumors, indicating that in these tumors biallelic VHL gene inactivation occurred.
In addition to RET, VHL and NF-1, genes encoding succinate dehydrogenase complex subunit B (SDHB), subunit C (SDHC), and subunit D (SDHD) are recognized as susceptibility genes for PCC and PGL.
The current case of carotid body paraganglioma in patient with the 393C>A (N131K) missense mutation in the VHL gene, supports association of this specific mutation and VHL disease type 2, and suggests its correlation with susceptibility to paragangliomas.
Pheochromocytomas and paragangliomas are neuroendocrine tumors that occur in the context of inherited cancer syndromes in ∼30% of cases and are linked to germline mutations in the VHL, RET, NF1, SDHA, SDHB, SDHC, SDHD, SDHAF2 and TMEM127 genes.
Transcriptome studies indeed revealed that pheochromocytomas and paragangliomas can be classified into two major clusters depending on their gene expression profile: Cluster 1 comprises samples associated with a hypoxic signature such as SDHx- and VHL-related tumors and cluster 2 includes RET, NF1, and TMEM127-mutated tumors, as well as most of sporadic tumors.
Germline mutations in the susceptibility genes RET, SDHB, SDHD, and VHL have been reported in 7.5-24% of patients with pheochromocytoma (Pheo) or paraganglioma (PGL) and sporadic presentation.
Genetic analysis on known susceptibility genes for paragangliomas (VHL, RET, SDHB, SDHC, SDHD, and SDHAF2) was performed in 17 consecutive patients with head/neck paraganglioma (age range, 14-82 years) and 17 relatives.
The finding of somatic mutations in VHL and RET in an additional 10-15% of tumors has brought the proportion of all patients with PCC and/or PGL due to a genetic disruption in these genes to approximately one half.
No genetic alterations to the VHL and SDHB genes were detected in either the tumor tissue or tissues adjacent to the tumor, which led us to rule out a hereditary syndrome that could explain the association between paraganglioma and chromophobe renal cell carcinoma in a patient with arterial hypertension.
Germline mutations in the RET, SDHA, SDHAF2, SDHB, SDHC, SDHD, MAX, TMEM127, NF1 or VHL genes are identified in about 30% of patients with pheochromocytoma or paraganglioma and somatic mutations in RET, VHL or MAX genes are reported in 17% of sporadic tumors.
The dysfunction of genes involved in the cellular response to hypoxia, such as VHL, EGL nine homolog 1, and the succinate dehydrogenase (SDH) genes, leads to a direct abrogation of hypoxia inducible factor (HIF) degradation, resulting in a pseudo-hypoxic state implicated in PCC/PGL development.
PCC/PGL are still thought of as the "tumor of tens," with 10 % being hereditary; however, recent population based studies suggest that up to 32 % of patients have a germline mutation in one of the known common susceptibility genes (including NF1, VHL, RET, SDHB, SDHD, and SDHC).
Pheochromocytomas (PHEOs) and paragangliomas (PGLs) related to mutations in the mitochondrial succinate dehydrogenase (SDH) subunits A, B, C, and D, SDH complex assembly factor 2, and the von Hippel-Lindau (VHL) genes share a pseudohypoxic expression profile.
Identification of somatic VHL gene mutations in sporadic head and neck paragangliomas in association with activation of the HIF-1α/miR-210 signaling pathway.
For the VHL gene we found increased MetI in tumors as compared with normal adrenals (57% vs. 27%; P<0.001), in malignant vs. benign tumors (63% vs. 55%; P<0.05), and in PGL vs. PCC (66% vs. 55%; P<0.0005).