Description:
MULTIPLE ENDOCRINE NEOPLASIA, TYPE IIB; MEN2B
RET PROTOONCOGENE; RET
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Repository
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NIGMS Human Genetic Cell Repository
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| Subcollection |
Heritable Diseases
Hereditary Cancers |
| Class |
Heritable Cancer Syndromes and other Cancers |
| Quantity |
25 µg |
| Quantitation Method |
Please see our FAQ |
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Biopsy Source
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Peripheral vein
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Cell Type
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B-Lymphocyte
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Tissue Type
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Blood
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Transformant
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Epstein-Barr Virus
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Sample Source
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DNA from LCL
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Race
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White
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Relation to Proband
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proband
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Confirmation
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Clinical summary/Case history
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Species
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Homo sapiens
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Common Name
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Human
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Remarks
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| IDENTIFICATION OF SPECIES OF ORIGIN |
Species of Origin Confirmed by Nucleoside Phosphorylase, Glucose-6-Phosphate Dehydrogenase, and Lactate Dehydrogenase Isoenzyme Electrophoresis |
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| Gene |
RET |
| Chromosomal Location |
10q11.2 |
| Allelic Variant 1 |
164761.0013; MULTIPLE ENDOCRINE NEOPLASIA, TYPE IIB |
| Identified Mutation |
MET918THR; In all 9 unrelated MEN2B patients studied, Hofstra et al. (1994) found a mutation in codon 918 of the RET gene, causing the substitution of a threonine for a methionine in the tyrosine kinase domain of the protein. They found the same mutation in 6 out of 18 sporadic medullary thyroid carcinomas. This conclusively demonstrates that MEN2A and MEN2B are related as allelic disorders; there is thus no justification for calling MEN2B MEN3. This identical point mutation in the catalytic core of the tyrosine kinase domain of RET was also found in association with both inherited and de novo MEN2B by Carlson et al. (1994) and Eng et al. (1994). The ATG-to-ACG mutation results in the substitution of threonine for methionine at codon 918 in the codon designation of Takahashi et al. (1988, 1989). Carlson et al. (1994) proposed that this amino acid replacement affects substrate interactions and results in oncogenic action by the RET protein. It is noteworthy that most mutations identified in cases of MEN2A and familial medullary thyroid carcinoma have been contained within the extracellular ligand-binding domain of the RET protooncogene and have resulted in nonconservative substitutions for 4 different cysteines. MEN2B has shown mainly noncysteine substitutions.
The existence of polymorphic markers tightly linked to MEN2B and the fact that the M918T mutation accounts for almost all cases of MEN2B enabled Carlson et al. (1994) to determine unequivocally whether mutations occurred on the maternal or paternal chromosome. Strikingly, all 25 of the mutations they analyzed occurred in the paternal allele. Therefore, MEN2B can be added to the list of neoplastic diseases, which already includes Wilms tumor, bilateral retinoblastoma, osteosarcoma, embryonal rhabdomyosarcoma, and neurofibromatosis type I, for which the relevant genetic alteration occurs either predominantly or exclusively on the paternally derived chromosome. Carlson et al. (1994) also observed a paternal age effect.
Santoro et al. (1995) demonstrated that this RET allele is a transforming gene in NIH 3T3 cells as a consequence of constitutive activation of the RET kinase. The mutation alters RET catalytic properties both quantitatively and qualitatively.
Eng et al. (1995) analyzed 71 sporadic medullary thyroid carcinomas (68 primary tumors and 3 cell lines) for mutations in RET exons 10, 11, and 16. They found that 23% of sporadic MTC had RET codon 918 mutations (located in exon 16), while only 3% had exon 10 mutations and none had mutations in exon 11. They found no exon 16 mutations in MTC from 14 MEN2A cases. Thus, exon 10 and 11 mutations, commonly found in familial MTC and MEN2A, rarely occur in sporadic MTC; somatic mutation of RET codon 918 appears to play a role in the tumorigenesis of a significant minority of sporadic MTC but not in MEN2A tumors. In addition to their biologic interest, these findings may have clinical application in determining whether a case presenting with isolated MTC is truly sporadic or is part of an inherited cancer syndrome. The codon 918 mutation was altered methionine (ATG) to threonine (ACG) in all instances in which germline DNA was available for analysis, it was found to be wildtype. This mutation was previously designated MET664THR.
In MEN2A, mutations affecting cysteine residues in the extracellular domain of the receptor tyrosine kinase cause constitutive activation of the tyrosine kinase by the formation of disulfide-bonded homodimers. In MEN2B, only the met918-to-thr mutation in the tyrosine kinase domain has been identified. This mutation does not lead to dimer formation, but has been shown both biologically and biochemically to cause ligand-independent activation of the RET protein, but to a lesser extent than MEN2A mutations. Bongarzone et al. (1998) showed that the activity of the MEN2B RET mutation could be increased by stable dimerization of the receptor. Dimerization was achieved experimentally by constructing a double mutant receptor with a MEN2A mutation (cys634 to arg; 164761.0011) in addition to the MEN2B mutation, and by chronic exposure of the cells expressing the met918-to-thr mutation of RET to the RET ligand glial cell line-derived neurotrophic factor (GDNF; 600837). In both cases, full activation of the RET-MEN2B mutant protein, measured by in vitro transfection assays and biochemical parameters, was seen. These results indicated that the MEN2B phenotype could be influenced by the tissue distribution or concentration of RET ligand(s).
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| Remarks |
Clinically affected; oral mucosal neuromas; medullary thyroid carcinoma; bilateral pheochromocytoma; marphanoid body habitus; negative family history; donor subject has a T>C transition (ATG>ACG) in exon 16 of the RET gene resulting in the substitution of threonine for methionine at codon 918 [Met918Thr (M918T)] |
| Margraf RL, Mao R, Wittwer CT, Rapid diagnosis of MEN2B using unlabeled probe melting analysis and the LightCycler 480 instrument The Journal of molecular diagnostics : JMD10:123-8 2008 |
| PubMed ID: 18258924 |
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| Margraf RL, Mao R, Highsmith WE, Holtegaard LM, Wittwer CT, Mutation scanning of the RET protooncogene using high-resolution melting analysis Clinical chemistry52:138-41 2006 |
| PubMed ID: 16391329 |
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