SDH Mutations in Patients Affected by Paraganglioma Syndromes: A Personal Experience

Targeted next-generation sequencing detects rare genetic events in pheochromocytoma and paraganglioma

Background

Knowing the genetic status of patients affected by paragangliomas and pheochromocytomas (PPGL) is important for the guidance of their management and their relatives. Our objective was to improve the diagnostic performances of PPGL genetic testing by next-generation sequencing (NGS).

Methods

We developed a custom multigene panel, which includes 17 PPGL genes and is compatible with both germline and tumour DNA screening. The NGS assay was first validated in a retrospective cohort of 201 frozen tumour DNAs and then applied prospectively to 623 DNAs extracted from leucocytes, frozen or paraffin-embedded PPGL tumours.

Results

In the retrospective cohort, the sensitivity of the NGS assay was evaluated at 100% for point and indels mutations and 86% for large rearrangements. The mutation rate was re-evaluated from 65% (132/202) to 78% (156/201) after NGS analysis. In the prospective cohort, NGS detected not only germline and somatic mutations but also co-occurring variants and mosaicism. A mutation was identified in 74% of patients for whom both germline and tumour DNA were available.

Conclusion

The analysis of 824 DNAs from patients with PPGL demonstrated that NGS assay significantly improves the performances of PPGL genetic testing compared with conventional methods, increasing the rate of identified mutations and identifying rare genetic mechanisms.

SDH mutations in tumorigenesis and inherited endocrine tumours: lesson from the phaeochromocytoma-paraganglioma syndromes

A genetic predisposition for paragangliomas and adrenal or extra-adrenal phaeochromocytomas was recognized years ago. Beside the well-known syndromes associated with an increased risk of adrenal phaeochromocytoma, Von Hippel Lindau disease, multiple endocrine neoplasia type 2 and neurofibromatosis type 1, the study of inherited predisposition to head and neck paragangliomas led to the discovery of the novel 'paraganglioma-phaeochromocytoma syndrome' caused by germline mutations in three genes encoding subunits of the succinate dehydrogenase (SDH) enzyme (SDHB, SDHC and SDHD) thus opening an unexpected connection between mitochondrial tumour suppressor genes and neural crest-derived cancers. Germline mutations in SDH genes are responsible for 6% and 9% of sporadic paragangliomas and phaeochromocytomas, respectively, 29% of paediatric cases, 38% of malignant tumours and more than 80% of familial aggregations of paraganglioma and phaeochromocytoma. The disease is characterized by autosomal dominant inheritance with a peculiar parent-of-origin effect for SDHD mutations. Life-time tumour risk seems higher than 70% with variable clinical manifestantions depending on the mutated gene. In this review we summarize the most recent knowledge about the role of SDH deficiency in tumorigenesis, the spectrum and prevalence of SDH mutations derived from several series of cases, the related clinical manifestantions including rare phenotypes, such as the association of paragangliomas with gastrointestinal stromal tumours and kidney cancers, and the biological hypotheses attempting to explain genotype to phenotype correlation.

Predominant expression of mutated allele of the succunate dehydrogenase D (SDHD) gene in the SDHD-related paragangliomas

Recent studies indicate that succinate dehydrogenase (SDH) genes B, C, or D are, at least partly, involved in the pathogenesis of pheochromocytoma or paraganglioma. Of these three genes, the SDHD gene mutation is most closely related with paragangliomas of the neck. Here we describe a case of an SDHD-related paraganglioma, in which we studied the molecular characteristics of an SDHD mutation to evaluate the involvement of SDHD in neck paragangliomas. Genetic testing revealed a heterozygous G106D mutation in the SDHD gene. In the tumor tissue, loss of heterozygosity was demonstrated by real time polymerase chain reaction (PCR). In the present case of SDHD mutated paragangliomas, wild type SDHD gene expression was markedly reduced possibly due to loss of heterozygosity not due to imprinting of SDHD gene in the tumors.

A case of malignant pheochromocytoma with Holt-Oram syndrome

A 23-year-old female patient with malignant pheochromocytoma was admitted to the Tokyo Women's Medical University. The patient had been clinically diagnosed with Holt-Oram syndrome at birth. Since she had complex congenital heart disease, chronic heart failure, and severe hypoxia, the risk surrounding surgery to remove the primary tumor was predicted to be very high, and subsequently, chemotherapy was performed. The patient was not able to continue chemotherapy due to adverse effects. However, for one year, both her hypertension and catecholamine-dependent symptoms were well controlled by an alpha-adrenergic and beta-adrenergic receptor blockade, although the patient did experience high plasma norepinephrine levels. To our knowledge, this is the first report of a patient with the combination of malignant pheochromocytoma and Holt-Oram syndrome. A correlation between chronic hypoxia and pheochromocytoma has been reported. This instructive case reminds us to consider the possibility of pheochromocytoma with congenital heart disease when these types of unexpected or unusual symptoms are encountered.

Soft tissue tumors of the urinary bladder, Part I: myofibroblastic proliferations, benign neoplasms, and tumors of uncertain malignant potential

Most bladder tumors arise from the urothelium. However, there are several uncommon but significant bladder lesions that must be differentiated from urothelial carcinomas. These include both benign and malignant spindle cell lesions. The first half of this 2-part review will describe benign myofibroblastic proliferations including inflammatory myofibroblastic tumor and postoperative spindle cell nodule; benign neoplasms including leiomyoma, hemangioma, neurofibroma, and schwannoma; and tumors of uncertain malignant potential including paraganglioma, granular cell tumor, and perivascular epithelioid cell tumor. Common clinical presentations, morphological characteristics, and immunohistochemical features are described to aid the practicing pathologist in the identification of these entities. This review also describes current theories as to the pathogenesis of inflammatory myofibroblastic tumor and postoperative spindle cell nodule and details the current molecular markers identifying several of these lesions.