Variant type is associated with disease characteristics in SDHB, SDHC and SDHD-linked phaeochromocytoma-paraganglioma.

BACKGROUND: Pathogenic germline variants in subunits of succinate dehydrogenase (SDHB, SDHC and SDHD) are broadly associated with disease subtypes of phaeochromocytoma-paraganglioma (PPGL) syndrome. Our objective was to investigate the role of variant type (ie, missense vs truncating) in determining tumour phenotype. METHODS: Three independent datasets comprising 950 PPGL and head and neck paraganglioma (HNPGL) patients were analysed for associations of variant type with tumour type and age-related tumour risk. All patients were carriers of pathogenic germline variants in the SDHB, SDHC or SDHD genes. RESULTS: Truncating SDH variants were significantly over-represented in clinical cases compared with missense variants, and carriers of SDHD truncating variants had a significantly higher risk for PPGL (p<0.001), an earlier age of diagnosis (p<0.0001) and a greater risk for PPGL/HNPGL comorbidity compared with carriers of missense variants. Carriers of SDHB truncating variants displayed a trend towards increased risk of PPGL, and all three SDH genes showed a trend towards over-representation of missense variants in HNPGL cases. Overall, variant types conferred PPGL risk in the (highest-to-lowest) sequence SDHB truncating, SDHB missense, SDHD truncating and SDHD missense, with the opposite pattern apparent for HNPGL (p<0.001). CONCLUSIONS: SDHD truncating variants represent a distinct group, with a clinical phenotype reminiscent of but not identical to SDHB. We propose that surveillance and counselling of carriers of SDHD should be tailored by variant type. The clinical impact of truncating SDHx variants is distinct from missense variants and suggests that residual SDH protein subunit function determines risk and site of disease.

Risk of malignant paraganglioma in SDHB-mutation and SDHD-mutation carriers: a systematic review and meta-analysis.

The main objective of this study was to perform a systematic review and meta-analysis on the risk of developing malignant paraganglioma (PGL) in SDHB-mutation and SDHD-mutation carriers. PubMed, EMBASE, Web of Science, COCHRANE and Academic Search Premier (2000-August 2011) and references of key articles were searched to identify potentially relevant studies. The main outcomes were the pooled incidence and prevalence of malignant PGL in SDHB-mutation and SDHD-mutation carriers. A meta-analysis was performed with an exact likelihood approach using a logistic regression with a random effect at the study level. Twelve studies were included. The pooled incidence of malignant PGL in populations comprising both asymptomatic mutation carriers and mutation carriers with manifest non-malignant PGL was 17% (95% CI 10 to 28) for SDHB-mutation carriers and 8% (95% CI 2 to 26) for SDHD-mutation carriers. The pooled risk in prevalence studies was 13% (95% CI 4 to 34) and 4% (95% CI 2 to 7), respectively. In studies comprising only mutation carriers with manifest disease, the pooled prevalence was 23% (95% CI 16 to 33) for SDHB-mutation and 3% (95% CI 1 to 10) for SDHD-mutation carriers. Incidence and prevalence of malignant PGL are higher in SDHB-mutation than in SDHD-mutation carriers, but lower in SDHB-mutation carriers than hitherto appreciated.

Intraoperative detection of ganglioneuromas with 123I-MIBG.

Radioactive MIBG can be used in radioguided surgery for neuroendocrine tumors. We report the case of a man with a mutation in the succinate dehydrogenase subunit B (SDHB) gene, in which an abdominal MRI scan identified two 5-mm left para-aortic nodules, suspect for paragangliomas. Subsequent SPECT revealed increased uptake of tracer. 123I MIBG probe-guided resection was scheduled. During surgery, 2 small nodules with elevated activity in between the superior mesenteric artery and the left adrenal gland were identified by the detection probe and were resected. Histopathologic examination revealed mature ganglioneuromas.