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The RET protooncogene in sporadic pheochromocytomas: frequent MEN 2-like mutations and new molecular defects
C Beldjord1, F Desclaux-Arramond, M Raffin-Sanson
1INSERM U-129, Institut Cochin de Génétique Moléculaire, Université René Descartes, Paris, France.
Abstract:
To assess the pathophysiological role of the RET protooncogene in sporadic pheochromocytomas, we examined the 2 regions of the gene in which molecular defects are specifically associated with the multiple endocrine neoplasias (MEN) type 2A (the cysteine-rich domain encoded by exons 10 and 11), and type 2B (the tyrosine kinase domain encoded by exon 16). The sequences of both regions were amplified by reverse transcriptase-polymerase chain reaction (PCR) or PCR from tumor RNA and/or leukocyte DNA. The amplified fragments were analyzed by denaturing gradient gel electrophoresis using chemical clamps. In 28 patients with unilateral sporadic tumors, 6 RET mutations were found, 3 in the MEN 2A region, 3 in the MEN 2B region. Five patients had missense mutations: 2 in the MEN 2A region (C634W and D631Y), and 3 in the MEN 2B region (M918T). Analysis of leukocyte DNA in 3 of these patients confirmed that RET mutations were only present in tumor DNA. The sixth patient had lost exon 10 in the tumor complementary DNA as a result of the deletion of the dinucleotide -AG- at the 3'splice acceptor site of intron 9; this molecular defect was only found in the tumor DNA. Thus RET mutations of the MEN 2A and 2B regions are also found in about 20% of sporadic pheochromocytomas. We describe new types of molecular defects of the RET protooncogene in the MEN 2A region that involve noncysteine residues and loss of exon 10. Further studies should be extended to analyze the entire RET protooncogene. These findings have a profound clinical impact for the management of patients with supposedly sporadic pheochromocytomas.
Insights
RET protooncogene mutations are found in approximately 20% of sporadic pheochromocytomas, impacting patient management. New RET gene defects in the MEN 2A region were identified, affecting noncysteine residues and exon 10.
Area of Science:
- Oncology
- Genetics
- Endocrinology
Background:
- Pheochromocytomas are tumors of the adrenal medulla.
- The RET protooncogene is implicated in Multiple Endocrine Neoplasia (MEN) types 2A and 2B.
- The role of RET mutations in sporadic pheochromocytomas requires further investigation.
Purpose of the Study:
- To investigate the pathophysiological role of the RET protooncogene in sporadic pheochromocytomas.
- To identify RET gene mutations in specific regions associated with MEN 2A and MEN 2B.
- To determine the frequency and nature of RET mutations in sporadic pheochromocytomas.
Main Methods:
- Reverse transcriptase-polymerase chain reaction (RT-PCR) and PCR were used to amplify RET gene regions.
- Denaturing gradient gel electrophoresis with chemical clamps analyzed amplified fragments.
- Sequencing of tumor RNA and/or leukocyte DNA from patients with sporadic pheochromocytomas.
Main Results:
- Six RET mutations were identified in 28 patients with sporadic pheochromocytomas (approximately 20% prevalence).
- Mutations included missense mutations in both MEN 2A (C634W, D631Y) and MEN 2B (M918T) regions.
- A novel defect involving loss of exon 10 due to a splice site mutation was found in tumor DNA only.
Conclusions:
- RET protooncogene mutations are present in a significant subset of sporadic pheochromocytomas.
- New types of RET mutations, including non-cysteine residue alterations and exon deletions, were identified.
- These findings have clinical implications for diagnosing and managing patients with seemingly sporadic pheochromocytomas.