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

Abstract

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.

Figure 1. Spectrum of germline mutations identified in SDHB (1.1), SDHD (1.2) and SDHC (1.3) genes

For each SDH gene, the left imagine shows numbers and percentages of the different types of mutations including missense (MS), in-frame deletion/insertion (IF del/ins), frame-shift (FS), nonsense (NS), splice-site (SS) and large genomic deletions (LD). The right histogram shows the distribution of point mutations along the coding exons of each gene (blue bar = total of mutations, purple bar = missense and in-frame insertion/deletion, light-yellow bar = truncating mutations).

Figure 2. Clinical manifestations of SDHB (2.1), SDHD (2.2) and SDHC (2.3) affected carriers

For each SDH gene the left histogram shows the distribution of ages at diagnosis of the first tumour. The range, median and mean ages are also resumed. The right imagine shows the percentages of various tumour phenotypes, including extra-adrenal paraganglioma alone (PGL, blue), adrenal pheochromocytoma with or without extra-adrenal PGLs (PHEO +/− PGL, azure), head and neck paraganglioma alone (HNpgl, yellow), head and neck PGLs with PHEO and/or PGL (HN +/− PHEO +/− PGL, green), renal cell cancer (RCC, pink), gastrointestinal stromal tumours (GIST, purple) with or without (+/−) other neuroendocrine tumours.