Pip Killick

Succinate dehydrogenase B (SDHB) and D (SDHD) subunit gene mutations predispose to adrenal and extraadrenal pheochromocytomas, head and neck paragangliomas (HNPGL), and other tumor types. We report tumor risks in 358 patients with SDHB (n=295) and SDHD (n=63) mutations. Risks of HNPGL and pheochromocytoma in SDHB mutation carriers were 29% and 52%, respectively, at age 60 years and 71% and 29%, respectively, in SDHD mutation carriers. Risks of malignant pheochromocytoma and renal tumors (14% at age 70 years) were higher in SDHB mutation carriers; 55 different mutations (including a novel recurrent exon 1 deletion) were identified. No clear genotype-phenotype correlations were detected for SDHB mutations. However, SDHD mutations predicted to result in loss of expression or a truncated or unstable protein were associated with a significantly increased risk of pheochromocytoma compared to missense mutations that were not predicted to impair protein stability (most such cases had the common p.Pro81Leu mutation). Analysis of the largest cohort of SDHB/D mutation carriers has enhanced estimates of penetrance and tumor risk and supports in silicon protein structure prediction analysis for functional assessment of mutations. The differing effect of the SDHD p.Pro81Leu on HNPGL and pheochromocytoma risks suggests differing mechanisms of tumorigenesis in SDH-associated HNPGL and pheochromocytoma.

Familial renal cell carcinoma (RCC) is a heterogeneous disorder that is most commonly caused by germline mutations in the VHL, MET, and FLCN genes or by constitutional chromosome 3 translocations. However, for many patients with familial RCC, the genetic basis of the disease is undefined. We investigated whether germline mutations in fumarate hydratase (FH) or succinate dehydrogenase subunit genes (SDHB, SDHC, SDHD) were associated with RCC susceptibility in 68 patients with no clinical evidence of an RCC susceptibility syndrome. No mutations in FH, SDHC, or SDHD were identified in probands, but 3 of the 68 (4.4%) probands had a germline SDHB mutation. Patients with a germline SDHB mutation presented with familial RCC (n = 1) or bilateral RCC (n = 2) and no personal or family history of pheochromocytoma or head and neck paraganglioma. Age at diagnosis of RCC in SDHB mutation carriers ranged from 24 to 73 years. These findings 1) demonstrate that patients with suspected inherited RCC should be examined for germline SDHB mutations, 2) suggest that all identified SDHB mutation carriers should be offered surveillance for RCC, and 3) provide a further link between familial RCC and activation of hypoxic-gene response pathways.

von Hippel-Lindau (VHL) disease is a dominantly inherited familial cancer syndrome resulting from mutations in the VHL tumor suppressor gene. VHL disease displays marked variation in expression and the presence of pheochromocytoma has been linked to missense VHL mutations. We analyzed genotype-phenotype correlations in 573 individuals with VHL disease. Routine clinical and radiological surveillance of VHL patients and at-risk relatives was associated with increased detection of retinal angiomatosis (73 vs. 59% of cases) and a reduction in age at diagnosis of renal cell carcinoma (RCC) (44.0+/-10.9 vs. 39.7+/-10.3 years). We confirmed the association of pheochromocytoma with missense mutations described previously, but stratifying missense mutations into those that resulted in substitution of a surface amino acid and those that disrupted structural integrity demonstrated that surface amino acid substitutions conferred a higher pheochromocytoma risk. Age at first manifestation of VHL disease was significantly earlier (P=0.001), and age-related risks of retinal angiomas and RCC were higher (P=0.022 and P=0.0008, respectively) in individuals with a nonsense or frameshift mutation than in those with deletions or missense mutations that disrupted the structural integrity of the VHL gene product (pVHL). These results extend genotype-phenotype-protein structure correlations in VHL disease and provide a baseline for future chemoprevention studies in VHL disease.

CONTEXT: Activation of the hypoxia-inducible transcription factors HIF-1 and HIF-2 and a HIF-independent defect in developmental apoptosis have been implicated in the pathogenesis of pheochromocytoma (PCC) associated with VHL, SDHB, and SDHD mutations. OBJECTIVE: Our objective was to compare protein (HIF-1alpha, EPAS1, SDHB, JunB, CCND1, CD34, CLU) and gene (VEGF, BNIP3) expression patterns in VHL and SDHB/D associated tumors. RESULTS: Overexpression of HIF-2 was relatively more common in VHL than SDHB/D PCC (12 of 13 vs. 14 of 20, P = 0.02), whereas nuclear HIF-1 staining was relatively more frequent in SDHB/D PCC (19 of 20 vs. 13 of 16, P = 0.04). In addition, CCND1 and VEGF expression (HIF-2 target genes) was significantly higher in VHL than in SDHB/D PCC. These findings suggest that VHL inactivation leads to preferential HIF-2 activation and CCND1 expression as described previously in VHL-defective renal cell carcinoma cell lines but not in other cell types. These similarities between the downstream consequences of VHL inactivation and HIF dysregulation in renal cell carcinoma and PCC may explain how inactivation of the ubiquitously expressed VHL protein results in susceptibility to specific tumor types. Both VHL and SDHB/D PCC demonstrated reduced CLU and SDHB expression. SDHB PCC are associated with a high risk of malignancy, and expression of (proapototic) BNIP3 was significantly lower in SDHB than VHL PCC. CONCLUSION: Although inactivation of VHL and SDHB/D may disrupt similar HIF-dependent and HIF-independent signaling pathways, their effects on target gene expression are not identical, and this may explain the observed clinical differences in PCC and associated tumors seen with germline VHL and SDHB/D mutations.

Von Hippel-Lindau (VHL) syndrome is a dominantly inherited familial cancer syndrome caused by mutations in the VHL gene. VHL syndrome displays marked variation in expression and analysis of genotype-phenotype correlations have led to the concept of four subtypes of VHL syndrome (Types 1, 2A-C). Type 2 subtypes of VHL syndrome are characterized by the presence of pheochromocytoma and the three Type 2 subtypes are associated with differing risks of hemangioblastoma and renal cell carcinoma (RCC). Type 2 VHL syndrome is usually associated with surface missense mutations. Type 1 VHL syndrome is most commonly caused by germline exon deletions and truncating mutations and is characterized by susceptibility to hemangioblastomas and RCC but not pheochromocytoma. Recently, it has been suggested that large VHL gene deletions involving C3orf10 (HSPC300) might be associated with a low risk of RCC. We have reviewed the molecular and clinical characteristics of 127 individuals with germline VHL gene deletions. Large VHL gene deletions associated with a contiguous loss of C3orf10 were associated with a significantly lower lifetime risk of RCC than deletions that did not involve C3orf10. The risks of hemangioblastomas were similar in both groups. These results add to the growing body of evidence suggesting that patients with VHL syndrome caused by large VHL deletions that include C3orf10 may be designated as having a specific subtype (Type 1B) of the disorder.