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Pitfalls in genetic analysis of pheochromocytomas/paragangliomas-case report
Letizia Canu1, Elena Rapizzi, Benedetta Zampetti
1Department of Experimental and Clinical Biomedical Sciences (L.C., E.R., B.Z., R.F., V.G., M.M.), and Department of Human Pathology and Oncology (G.N.), University of Florence, 50134 Florence, Italy; General and Surgical Unit (C.B., A.V.), and Endocrinology Unit, Careggi Hospital (G.P., T.E.), Azienda Ospedaliera Universitaria Careggi, 50134 Florence, Italy; Division of Clinical Neurochemistry (S.R., N.Q., G.E.), Institute of Clinical Chemistry and Laboratory Medicine and Department of Medicine, Dresden University of Technology, 01069 Dresden, Germany; and Istituto Toscano Tumori (M.M.), 50139 Florence, Italy.
Context:
About 35% of patients with pheochromocytoma/paraganglioma carry a germline mutation in one of the 10 main susceptibility genes. The recent introduction of next-generation sequencing will allow the analysis of all these genes in one run. When positive, the analysis is generally unequivocal due to the association between a germline mutation and a concordant clinical presentation or positive family history. When genetic analysis reveals a novel mutation with no clinical correlates, particularly in the presence of a missense variant, the question arises whether the mutation is pathogenic or a rare polymorphism.
Objective:
We report the case of a 35-year-old patient operated for a pheochromocytoma who turned out to be a carrier of a novel SDHD (succinate dehydrogenase subunit D) missense mutation. With no positive family history or clinical correlates, we decided to perform additional analyses to test the clinical significance of the mutation.
Methods:
We performed in silico analysis, tissue loss of heterozygosity analysis, immunohistochemistry, Western blot analysis, SDH enzymatic assay, and measurement of the succinate/fumarate concentration ratio in the tumor tissue by tandem mass spectrometry.
Results:
Although the in silico analysis gave contradictory results according to the different methods, all the other tests demonstrated that the SDH complex was conserved and normally active. We therefore came to the conclusion that the variant was a nonpathogenic polymorphism.
Conclusions:
Advancements in technology facilitate genetic analysis of patients with pheochromocytoma but also offer new challenges to the clinician who, in some cases, needs clinical correlates and/or functional tests to give significance to the results of the genetic assay.
