DiagnosisClinical DiagnosisMultiple endocrine neoplasia type 2 (MEN 2) includes the phenotypes MEN 2A, familial medullary thyroid carcinoma (FMTC), and MEN 2B.MEN 2A is diagnosed clinically by the occurrence of two or more specific endocrine tumors (medullary thyroid carcinoma [MTC], pheochromocytoma, or parathyroid adenoma/hyperplasia) in a single individual or in close relatives. Historically, familial medullary thyroid carcinoma (FMTC) is operationally diagnosed in families with four or more cases of MTC in the absence of pheochromocytoma or parathyroid adenoma/hyperplasia [Eng et al 1996, Zbuk & Eng 2007]. Because mutations in a single predisposition gene, RET, account for the clinical subtypes of MEN 2, FMTC including families with fewer than four cases is more accurately considered a matter of penetrance (see Penetrance).MEN 2B is diagnosed clinically by the presence of mucosal neuromas of the lips and tongue, as well as medullated corneal nerve fibers, distinctive facies with enlarged lips, an asthenic ‘marfanoid’ body habitus, and MTC [American Thyroid Association Guidelines Task Force 2009]. TestingMedullary thyroid carcinoma (MTC) and C-cell hyperplasia (CCH) Histologic. MTC originates in calcitonin-producing cells (C-cells) of the thyroid gland. MTC is diagnosed histologically when nests of C-cells appear to extend beyond the basement membrane and to infiltrate and destroy thyroid follicles. Immunohistochemistry for calcitonin expression may be performed as a pathologic diagnostic adjunct.
CCH is diagnosed histologically by the presence of an increased number of diffusely scattered or clustered C-cells. In MEN 2, the age of transformation from CCH to MTC varies with different germline RET mutations [Machens et al 2003]. Biochemical. MTC and CCH are suspected in the presence of an elevated plasma calcitonin concentration, a specific and sensitive marker. However, secondary CCH has been described occasionally in the setting of aging and hyperparathyroidism. Secondary CCH rarely transforms to MTC
In provocative testing, plasma calcitonin concentration is measured before (basal level) and two and five minutes after intravenous administration of calcium (stimulated level). Other calcitonin secretagogues are also used, such as pentagastrin (available in Europe, limited in the US). A basal or stimulated calcitonin level of ≥100 pg/mL is an indication for surgery [Costante et al 2007, American Thyroid Association Guidelines Task Force 2009].PheochromocytomaBiochemical. Pheochromocytoma is suspected when biochemical screening reveals elevated excretion of catecholamines and catecholamine metabolites (i.e., norepinephrine, epinephrine, metanephrine, and vanillylmandelic acid [VMA]) in plasma or 24-hour urine collections [Pacak et al 2005, Ilias & Pacak 2009]. In MEN 2, pheochromocytomas consistently produce epinephrine or epinephrine and norepinephrine [Ilias & Pacak 2009]. Imaging. Abdominal MRI and/or CT are performed whenever a pheochromocytoma is suspected clinically and whenever plasma or urinary catecholamine values are increased. MRI is more sensitive than CT in detection of a pheochromocytoma.
[¹⁸F]-fluorodopamine ([¹⁸F]DA) PET is the best overall imaging modality in the localization of pheochromocytomas. If [¹⁸F]DA PET is unavailable, MIBG (¹²³I- or ¹³¹I- metaiodobenzylguanidine) scintigraphy should be used for further evaluation of individuals with biochemical or radiographic evidence of pheochromocytoma [Ilias et al 2008]. Parathyroid abnormalities Biochemical. The diagnosis of parathyroid abnormalities is made when biochemical screening reveals simultaneously elevated serum concentrations of calcium and elevated or high-normal parathyroid hormone (PTH).Imaging. Postoperative parathyroid localizing studies with ^99mTc-sestamibi scintigraphy may be helpful if hyperparathyroidism recurs. For preoperative adenoma localization, three-dimensional single-photon emission CT (SPECT) may also be used [Brenner & Jacene 2008]. Molecular Genetic Testing Gene. RET is the only gene in which mutations are known to cause MEN 2. Clinical testing Table 1. Summary of Molecular Genetic Testing Used in MEN 2View in own windowGene SymbolPhenotypeTest MethodMutations DetectedMutation Detection Frequency by Test Method ^{1Test AvailabilityRETMEN 2ASequence analysis of select exonsSequence variants 2 in select exons 398% 4, 5ClinicalSequence analysis of coding regionSequence variants in exons & splice junctions>98% 5FMTC Sequence analysis of select exonsSequence variants in select exons 3 95% 6, 7Sequence analysis of coding regionSequence variants 2 >95% 6, 7MEN 2B Targeted mutation analysisp.Met918Thr, p.Ala883Phe 898% 9Sequence analysis of coding regionSequence variants 2 >98% 9MEN 2 or FMTCDeletion / duplication analysis 10None reportedUnknown; none reportedMEN 2 or FMTCLinkage analysis 11Not applicableNot applicable1. The ability of the test method used to detect a mutation that is present in the indicated gene.2. Examples of mutations detected by sequence analysis may include small intragenic deletions/insertions and missense, nonsense, and splice site mutations; typically, exonic or whole-gene deletions/duplications are not detected.3. Select exons vary by laboratory.4. Eng et al [1996], American Thyroid Association Guidelines Task Force [2009]5. Mutations of codon 634Cys occur in about 87% of families; mutation of cysteine residues at codons 609, 611, 618, and 620 together accounts for the majority of other identifiable mutations in exons 10 and 11 [Hansford & Mulligan 2000, Zbuk & Eng 2007, American Thyroid Association Guidelines Task Force 2009].6. Hansford & Mulligan [2000], American Thyroid Association Guidelines Task Force [2009]7. These mutations typically occur at one of the five cysteine residues (codons 609, 611, 618, 620, and 634) with mutations of codons 618, 620, and 634 each accounting for 20% to 30% of mutations. Other mutations in exons 5, 8, 10, 11, and 13 to 16 appear to account for a small percentage of mutations in families with FMTC, with an important minority affecting codons 768 and 804.8. Mutation panels may vary by laboratory.9. Approximately 95% of individuals with the MEN 2B phenotype have a single point mutation in the tyrosine kinase domain of RET at codon 918 in exon 16, which substitutes a threonine for methionine (p.Met918Thr) [Eng et al 1996]. A second mutation at codon 883 in exon 15, p.Ala883Phe, has been identified in several affected individuals without a p.Met918Thr mutation [Gimm et al 1997, Smith et al 1997]. Tandem RET mutations of codons 805, 806, and 904 in cis configuration with the p.Val804Met mutation have also been reported in individuals with MEN 2B [Miyauchi et al 1999, Menko et al 2002, Cranston et al 2006]. A single codon 804 mutation normally results in FMTC, and thus finding a p.Val804Met mutation in an individual with the MEN 2B phenotype is not surprising; however, the clinician should be aware that a second variant occurs in RET. Taken together, RET mutations have been found in more than 98% of individuals with MEN 2B [American Thyroid Association Guidelines Task Force 2009].10. Testing that identifies deletions/duplications not readily detectable by sequence analysis of the coding and flanking intronic regions of genomic DNA; included in the variety of methods that may be used are: quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), and chromosomal microarray (CMA) that includes this gene/chromosome segment.11. Linkage analysis may be an option to clarify the genetic status of at-risk relatives for families in which a RET mutation has not been identified. Samples from at least two affected family members are necessary to perform linkage analysis. The markers used in MEN 2 linkage analysis are very tightly linked to RET and accuracy may be greater than 95%. Note: The accuracy of linkage analysis is also dependent on (a) the informativeness of genetic markers in the affected individual's family and (b) the accuracy of the clinical diagnosis of MEN 2 in affected family members.Test characteristics. Information on test sensitivity, specificity, and other test characteristics can be found at www.eurogentest.org [Raue et al 2012].Interpretation of test results. For issues to consider in interpretation of sequence analysis results, click here.Information on specific allelic variants may be available in Molecular Genetics (see Table A. Genes and Databases and/or Pathologic allelic variants).Testing Strategy To confirm/establish the diagnosis in a proband. RET molecular genetic testing is indicated in all individuals with a diagnosis of MTC and a clinical diagnosis of MEN 2 or primary C-cell hyperplasia [Brandi et al 2001, American Thyroid Association Guidelines Task Force 2009]. The algorithm for testing is summarized in the most recent American Thyroid Association MTC Practice Guidelines [American Thyroid Association Guidelines Task Force 2009]. Features such as young age of onset, significant CCH, and/or multifocal disease suggest an inherited disorder.Note: The absence of family history or other features suggestive of a hereditary syndrome should not preclude molecular genetic testing for RET mutations.Persons with isolated MTC should be offered germline testing for exons 10, 11, and 13-16; ideally, testing should be completed preoperatively and with genetic counseling. In the setting of a clinical diagnosis of MEN 2A, sequencing of the entire RET coding region should be completed if exon specific testing is negative. For individuals with features suggestive of MEN 2B, targeted mutation analysis or sequencing of exons 15 and 16 to detect the p.Met918Thr and p.Ala883Phe mutations should be completed first. If negative, testing for p.Val804Met in exon 14 may be considered.RET molecular genetic testing may be warranted in persons presenting with adrenal pheochromocytoma. Testing algorithms for genes associated with paraganglioma and pheochromocytoma have been proposed based on age of onset, location, laterality, malignancy, and family history [Gimenez-Roqueplo et al 2006, Erlic et al 2009, Neumann et al 2009]. Exon 10 sequencing should be considered in individuals with Hirschsprung disease [American Thyroid Association Guidelines Task Force 2009] (see Hirschsprung Disease Overview).The differential diagnosis in persons with intestinal ganglioneuromatosis should include MEN 2B, and RET testing may be considered [American Thyroid Association Guidelines Task Force 2009]. Cutaneous lichen amyloidosis of the central upper back may prompt molecular genetic testing for the presence of a codon 634 mutation [American Thyroid Association Guidelines Task Force 2009]. Predictive testing for at-risk asymptomatic family members requires prior identification of the disease-causing mutation in the family.Prenatal diagnosis and preimplantation genetic diagnosis (PGD) for at-risk pregnancies require prior identification of the disease-causing mutation in the family. Genetically Related (Allelic) DisordersRET mutations are associated with the following disorders:HSCR1. Hirschsprung disease (HSCR) is a disorder of the enteric plexus of the colon that typically results in enlargement of the bowel and constipation or obstipation in neonates. About 50% of familial cases and 35% of simplex cases (i.e., a single occurrence in a family) of HSCR are caused by germline loss-of-function mutations in the RET proto-oncogene and are designated HSCR1 [Kouvaraki et al 2005]. Germline mutations causing HSCR occur throughout the coding sequence of RET [Takahashi et al 1999]. Families and individuals harboring germline RET mutations in exon 10, especially affecting codons 618 and 620 often cosegregate MEN 2A/FMTC and HSCR [Eng et al 1996, American Thyroid Association Guidelines Task Force 2009].Papillary thyroid carcinoma (PTC). Approximately 20%-40% of PTC is associated with somatic gene rearrangements that cause juxtaposition of the tyrosine kinase domain of RET to various gene partners [Tallini et al 1998, Santoro et al 2002, Puxeddu et al 2003].}

Natural HistoryThe endocrine disorders observed in MEN 2 are medullary thyroid carcinoma (MTC) and/or its precursor, C-cell hyperplasia; pheochromocytoma; and parathyroid adenoma or hyperplasia. MTC in persons with MEN 2 typically presents at a younger age than sporadic MTC and is more often associated with C-cell hyperplasia as well as multifocality or bilaterality. Symptoms of MTC include neck pain, a palpable neck mass, and/or diarrhea resulting from hypercalcitoninemia [Callender et al 2008]. Metastatic spread to cervical and regional lymph nodes (i.e., parathyroid, paratracheal, jugular chain, and upper mediastinum) or to distant sites including the liver, lungs, or bone is common and has often occurred in individuals with a palpable thyroid mass or diarrhea [Moley et al 1998, Cohen & Moley 2003]. Although pheochromocytomas rarely metastasize, they can be lethal because of intractable hypertension or anesthesia-induced hypertensive crises. Parathyroid abnormalities can range from benign parathyroid adenomas to clinically evident hyperparathyroidism with hypercalcemia and renal stones. MEN 2 is classified into three clinical subtypes: MEN 2A, FMTC, and MEN 2B (Table 2). All three subtypes involve high risk for MTC; MEN 2A and MEN 2B have an increased risk for pheochromocytoma; MEN 2A has an increased risk for parathyroid hyperplasia or adenoma. Classifying an individual or family by MEN 2 subtype is useful for determining prognosis and management. Table 2. Percent of Clinical Features by MEN 2 SubtypeView in own windowSubtype Medullary Thyroid Carcinoma Pheochromocytoma Parathyroid Disease MEN 2A 95% 50% 20%-30% FMTC 100% 0% 0% MEN 2B 100% 50% Uncommon MEN 2AThe MEN 2A subtype constitutes approximately 70%-80% of cases of MEN 2. Since genetic testing for RET mutations has become available, it has become apparent that 95% of individuals with MEN 2A develop MTC, about 50% develop pheochromocytoma, and about 20%-30% develop hyperparathyroidism [Eng et al 1996]. MTC is generally the first manifestation of MEN 2A. Probands with MTC typically present with a neck mass or neck pain prior to age 35 years. Up to 70% of such individuals already have cervical lymph node metastases [Cohen & Moley 2003]. Diarrhea, the most frequent systemic symptom, occurs in affected individuals with a plasma calcitonin concentration of more than 10 ng/mL and implies a poor prognosis. All individuals with an MTC-predisposing mutation who have not undergone prophylactic thyroidectomy demonstrate biochemical evidence of MTC by age 35 years [DeLellis et al 2004].Pheochromocytomas usually present after MTC or concomitantly; however, they are the first sign in 13%-27% of individuals with MEN 2A [Inabnet et al 2000, Rodriguez et al 2008]. Pheochromocytomas in persons with MEN 2A are diagnosed at an earlier age, have subtler symptoms, and are more likely to be bilateral than sporadic tumors [Pomares et al 1998, Pacak et al 2005]. Malignant transformation occurs in about 4% of cases [Modigliani et al 1995]. Since pheochromocytoma can be the first manifestation of MEN 2A, the diagnosis of pheochromocytoma in an individual warrants further investigation for MEN 2A [Inabnet et al 2000, Neumann et al 2002]. Hyperparathyroidism in MEN 2A is typically mild and may range from a single adenoma to marked hyperplasia. Most individuals with hyperparathyroidism have no symptoms; however, hypercalciuria and renal calculi may occur [Brandi et al 2001]. HPT usually presents many years after the diagnosis of MTC; the average age at onset is 38 years [American Thyroid Association Guidelines Task Force 2009].A small number of families with MEN 2A have pruritic cutaneous lichen amyloidosis (PCLA), also known as cutaneous lichen amyloidosis (CLA). This lichenoid skin lesion is located over the upper portion of the back and may appear before the onset of MTC [Seri et al 1997]. FMTCThe FMTC subtype constitutes approximately 10%-20% of cases of MEN 2. By operational definition MTC is the only clinical manifestation of FMTC. The age of onset of MTC is later in FMTC and the penetrance of MTC is lower than that observed in MEN 2A and MEN 2B [Eng et al 1996, Machens et al 2001, Machens & Dralle 2006, Zbuk & Eng 2007, American Thyroid Association Guidelines Task Force 2009]. To avoid erroneously ruling out the risk for pheochromocytoma, strict criteria should be met before a family is classified as having FMTC. In the past, some believed that a kindred with FMTC should have more than ten members with a RET mutation and multiple individuals with a RET mutation over age 50 years, and all members should have an adequate medical history demonstrating absence of pheochromocytoma or hyperparathyroidism [Brandi et al 2001]. Today, FMTC is typically viewed as a variant of MEN 2A with decreased penetrance of pheochromocytoma and hyperparathyroidism, rather than a distinct subtype [American Thyroid Association Guidelines Task Force 2009]. MEN 2BThe MEN 2B subtype accounts for approximately 5% of cases of MEN 2. MEN 2B is characterized by the early development of an aggressive form of MTC in all affected individuals [Skinner et al 1996]. Individuals with MEN 2B who do not undergo thyroidectomy at an early age (age <1 year) are likely to develop metastatic MTC at an early age. Prior to intervention with early prophylactic thyroidectomy, the average age of death in individuals with MEN 2B was 21 years. Pheochromocytomas occur in 50% of individuals with MEN 2B; about half are multiple and often bilateral. Individuals with undiagnosed pheochromocytoma may die from a cardiovascular hypertensive crisis perioperatively. Clinically significant parathyroid disease is absent in MEN 2B. Individuals with MEN 2B may be identified in infancy or early childhood by the presence of mucosal neuromas on the anterior dorsal surface of the tongue, palate, or pharynx and a distinctive facial appearance. The lips become prominent (or ‘blubbery’) over time, and submucosal nodules may be present on the vermilion border of the lips. Neuromas of the eyelids may cause thickening and eversion of the upper eyelid margins. Prominent thickened corneal nerves may be seen by slit lamp examination. About 40% of affected individuals have diffuse ganglioneuromatosis of the gastrointestinal tract. Associated symptoms include abdominal distension, megacolon, constipation, or diarrhea. In one study of 19 individuals with MEN 2B, 84% reported gastrointestinal symptoms beginning in infancy or early childhood [Wray et al 2008]. About 75% of affected individuals have a marfanoid habitus, often with kyphoscoliosis or lordosis, joint laxity, and decreased subcutaneous fat. Proximal muscle wasting and weakness can also be seen.

Genotype-Phenotype CorrelationsMutations involving the cysteine codons 609, 618, and 620 in exon 10 of RET are associated with MEN 2A, FMTC, and HSCR1 [Mulligan et al 1994, Decker et al 1998, Romeo et al 1998, Inoue et al 1999, Takahashi et al 1999]. Mutations in these codons, detected in about 10% of families with MEN 2A and more than 50% of families with FMTC, are associated with low transforming activity of RET [Takahashi et al 1998, Hansford & Mulligan 2000]. RET germline p.Met918Thr mutations are only associated with MEN 2B; however, somatic mutations at this codon are frequently observed in MTC in individuals with no known family history of MTC, and are over-represented in individuals with sporadic MTC who have a particular germline RET variant, c.2439C>T; p.Ser836Ser [Gimm et al 1999].Any RET mutation at codon 634 in exon 11 results in a higher incidence of pheochromocytomas and hyperparathyroidism [Eng et al 1996, Yip et al 2003, Zbuk & Eng 2007, American Thyroid Association Guidelines Task Force 2009].A report of 12 Brazilian families indicated that p.Cys634Arg is associated with a higher probability of having metastases at diagnosis than other codon 634 mutations [Puñales et al 2003]. Codon 634 mutations are also associated with development of cutaneous lichen amyloidosis [Seri et al 1997]. Among 25 individuals from three families with a codon 634 mutation, 36% had cutaneous lichen amyloidosis [Verga et al 2003]. While 25% of FMTC kindreds harbor a mutation in codon 634, p.Cys634Arg mutations are virtually absent in this subtype [Hansford & Mulligan 2000, Zbuk & Eng 2007].Mutations at codons 768, 804, and 891 that were initially only associated with MTC have subsequently been found in families with MEN 2A [Jimenez et al 2004a, Aiello et al 2005, Schulte et al 2010]. Initially thought to be associated with MTC only, mutations at codon 804 in exon 14 (i.e., p.Val804Leu and p.Val804Met) were subsequently identified in individuals with pheochromocytoma [Nilsson et al 1999, Høie et al 2000, Gibelin et al 2004, Jimenez et al 2004a]. Disease expression of mutations at codon 804 has been shown to be highly variable, even within the same family [Feldman et al 2000, Frohnauer & Decker 2000]. Some individuals with such mutations have MTC at age five years and fatal metastatic MTC at age 12 years, whereas other individuals with the same mutation have been shown to have normal thyroid histology at age 27 years, normal biochemical screening at age 40 years, and no clinical evidence of MTC at age 86 years. In another large family with a high level of consanguinity, biochemical testing indicated expression of thyroid disease in individuals homozygous but not heterozygous for p.Val804Met [Lecube et al 2002]. Cutaneous lichen amyloidosis in the background of a p.Val804Met mutation has been reported in one individual [Rothberg et al 2009].One study suggests that in addition to their association with MTC, mutations in codons 790 or 804 may be associated with papillary thyroid carcinoma [Brauckhoff et al 2002]. In a large Italian family, 40% of family members with a p.Val804Met mutation who were examined in detail had concomitant medullary and papillary thyroid carcinoma [Shifrin et al 2009]. The American Thyroid Association Guidelines Task Force has classified mutations based on their risk for aggressive MTC [American Thyroid Association Guidelines Task Force 2009] (Table 3).The classification may be used in (1) predicting phenotype and in (2) recommendations regarding the ages at which to (a) perform prophylactic thyroidectomy and (b) begin biochemical screening for pheochromocytoma and hyperparathyroidism (see Management, Surveillance).Table 3. Risk for Aggressive MTC Based on GenotypeView in own windowATA ¹ Risk LevelMutations ^{2, 3Level D
(highest risk)p.Ala883Phe
p.Met918Thr
p.Val804Met+p.Glu805Lys 4p.Val804Met+p.Tyr806Cys 4p.Val804Met+p.Ser904Cys 4Level Cp.Cys634Arg/Gly/Phe/Ser/Trp/TyrLevel Bp.Cys609Phe/Arg/Gly/Ser/Tyr
p.Cys611Arg/Gly/Phe/Ser/Trp/Tyr
p.Cys618Arg/Gly/Phe/Ser/Tyr
p.Cys620Arg/Gly/Phe/Ser/Trp/Tyr
p.Cys630Arg/Phe/Ser/Tyr
p.Asp631Tyr
p.633/9 bp dup
p.634/12 bp dup
p.Val804Met+p.Val778Ile 4Level Ap.Arg321Gly
p.531/9 bp dup
p.532 dup
p.Cys515Ser
p.Gly533Cys
p.Arg600Gln
p.Lys603Glu
p.Tyr606Cys
p.635/insert ELCR;p.Thr636Pro
p.Lys666Glu
p.Glu768Asp
p.Asn777Ser
p.Leu790Phe
p.Val804Leu/Met
p.Gly819Lys
p.Arg833Cys
p.Arg844Gln
p.Arg866Trp
p.Ser891Ala
p.Arg912Pro1. ATA = American Thyroid Association 2. p.Ser649Leu and p.Tyr791Phe have been removed from this list as they have been reclassified as polymorphisms [Erlic et al 2010].3. Mutation designations have not been edited by GeneReviews staff and may not be standard nomenclature.4. Mutations in cis on one allele}

Differential DiagnosisMTC in individuals with no family history of MTC. Medullary thyroid carcinoma accounts for approximately 10% of new cases of thyroid cancer diagnosed annually in the US. About 25%-30% of cases of MTC are caused by a germline RET mutation. Sporadic MTC tends to be unifocal, occur at a later age of onset, and lack C-cell hyperplasia (CCH) [American Thyroid Association Guidelines Task Force 2009]. The major issue is to distinguish individuals who have MEN 2 from those with isolated (nonsyndromic, nonfamilial) MTC. This is particularly relevant for individuals who present with multifocal MTC with a negative family history.In a large series of individuals with simplex medullary thyroid carcinoma (i.e., no known family history of MTC or personal history of other endocrine disease), approximately 7% were found to have disease-causing germline mutations in RET [Elisei et al 2007]. Genetic counseling and germline RET testing should be offered to all individuals with MTC, a clinical diagnosis of MEN 2, or primary CCH [American Thyroid Association Guidelines Task Force 2009]. DNA analysis of MTC tissue revealed a 40%-50% incidence of somatic RET mutations in the absence of a germline mutation [Schilling et al 2001, de Groot et al 2006, Dvorakova et al 2008, Elisei et al 2008]. The p.Met918Thr mutation is the most common; mutations at other codons as well as deletions have been reported [de Groot et al 2006]. Tumors with a somatic codon 918 mutation appear to be more aggressive [Schilling et al 2001, Elisei et al 2008]. C-cell hyperplasia (CCH). CCH associated with a positive calcitonin stimulation test occurs in about 5% of the general population. Serum calcitonin levels may be elevated in persons with chronic renal failure, sepsis, neuroendocrine tumors of the lung or gastrointestinal tract, hypergastrinemia, mastocytosis, autoimmune thyroid disease, and type 1A pseudohypoparathyroidism [Costante et al 2009]. Pheochromocytoma. The probability that pheochromocytoma is hereditary is estimated to be 84% for multifocal (including bilateral) tumors, and 59% for tumors with onset on or before age 18 years [Neumann et al 2002]. Approximately 25% of individuals with pheochromocytoma and no known family history of pheochromocytoma may have an inherited disease caused by a mutation in one of four genes: RET, VHL, SDHD, or SDHB [Neumann et al 2002, Bryant et al 2003]. The recently discovered pheochromocytoma susceptibility genes TMEM127, MAX, and SDHA further expand the differential diagnosis for nonsyndromic paraganglioma and pheochromocytoma [Burnichon et al 2010, Qin et al 2010, Comino-Mendez et al 2011]. Pacak et al [2005] compared biochemical profiles for inherited and sporadic pheochromocytoma. RET (MEN 2A). Approximately 5% of individuals with nonsyndromic pheochromocytoma and no family history of pheochromocytoma demonstrated a RET mutation [Neumann et al 2002].
MEN 2A accounted for more than 12% of individuals with hereditary pheochromocytoma being treated at a single institution, with 27% of those presenting with pheochromocytoma as the first manifestation of disease [Inabnet et al 2000].
It is also possible that a low-penetrance pheochromocytoma susceptibility locus exists in the 5' region of RET [McWhinney et al 2003]. VHL (von Hippel Lindau). Any individual presenting with a pheochromocytoma should be evaluated for von Hippel Lindau syndrome (VHL) [Erlic et al 2009]. VHL is characterized by pheochromocytoma, renal cell carcinoma, cerebellar and spinal hemangioblastoma, and retinal angioma.
Some families with apparent autosomal dominant pheochromocytoma have VHL mutations in the absence of other clinical manifestations of VHL [Inabnet et al 2000]. Neumann et al [2002] identified VHL mutations in 11% of individuals with nonsyndromic pheochromocytoma and no family history of pheochromocytoma.
The algorithm for prioritizing which gene to test is outlined by Erlic et al [2009].Hereditary paraganglioma-pheochromocytoma syndrome. Approximately 8.5% of individuals with apparently nonfamilial nonsyndromic pheochromocytoma have been shown to have a mutation in one of the succinate dehydrogenase subunit genes (SDHD or SDHB) that cause the hereditary paraganglioma-pheochromocytoma syndromes [Neumann et al 2002, Neumann et al 2004]. These genes are associated with familial paragangliomas, which are also known as extra-adrenal pheochromocytomas or glomus tumors [Baysal et al 2000, Astuti et al 2001]. While head and neck paragangliomas are common in individuals with SDHD and SDHB mutations, they are extremely rare in MEN 2 [Boedeker et al 2009]. Recent studies estimate that 1%-2% of individuals with familial or nonfamilial pheochromocytoma have a mutation in TMEM127 [Yao et al 2010, Abermil et al 2012]. A few individuals with mutations in TMEM127 have paragangliomas of the head/neck or at extra-adrenal sites [Neumann et al 2011]. MAX mutations are seen in approximately 1% of individuals with familial or nonfamilial pheochromocytoma [Burnichon et al 2012]. Korpershoek et al [2011] found SDHA germline mutations in 3% of individuals with apparently sporadic paragangliomas and pheochromocytomas. Pheochromocytomas are observed on occasion in neurofibromatosis type 1 (NF1). Multiple endocrine neoplasia type 1 (MEN 1). This endocrinopathy is genetically and clinically distinct from MEN 2; the similar nomenclature for MEN 1 and MEN 2 may cause confusion. MEN 1 is characterized by a triad of pituitary adenomas, pancreatic islet cell tumors, and parathyroid disease consisting of hyperplasia or adenoma. Affected individuals can also have adrenal cortical tumors, carcinoid tumors, and lipomas [Giraud et al 1998]. MEN 1 is caused by germline mutations in MEN1 and inherited in an autosomal dominant manner.Note to clinicians: For a patient-specific ‘simultaneous consult’ related to this disorder, go to , an interactive diagnostic decision support software tool that provides differential diagnoses based on patient findings (registration or institutional access required).FMTCMEN 2AMEN 2B

ManagementEvaluations Following Initial Diagnosis To establish the extent of disease in an individual diagnosed with MEN2, the biochemical, imaging, and genetic evaluations described in Diagnosis are recommended.Treatment of ManifestationsMedullary thyroid carcinoma (MTC). Standard treatment for MTC is surgical removal of the thyroid and lymph node dissection [American Thyroid Association Guidelines Task Force 2009]. Note: Chemotherapy and radiation are less effective in the treatment of MTC than surgical removal [Moley et al 1998, Cohen & Moley 2003]. All individuals who have undergone thyroidectomy need thyroid hormone replacement therapy. Autotransplantation of parathyroid tissue is not typically performed at the time of thyroidectomy unless there is evidence of hyperparathyroidism [American Thyroid Association Guidelines Task Force 2009]. Pheochromocytomas detected by biochemical testing and radionuclide imaging are removed by adrenalectomy, which may be performed using video-assisted laparoscopy. Historically, some specialists recommended bilateral adrenalectomy at the time of demonstration of tumor on just a single adrenal gland because of the strong probability that the other adrenal gland would develop a tumor within ten years. However, because of the risk for adrenal insufficiency and Addisonian crisis following bilateral adrenalectomy, most experts now recommend unilateral adrenalectomy in unilateral tumors and cortical-sparing adrenal surgery with close monitoring of the remnant tissue in persons with one remaining adrenal gland or bilateral pheochromocytoma [American Thyroid Association Guidelines Task Force 2009]. Hypertensive treatment prior to adrenalectomy involves the use of α- and β-adrenergic receptor blockade [Pacak et al 2005].Parathyroid adenoma or hyperplasia diagnosed at the time of thyroidectomy is treated either with resection of the visibly enlarged parathyroid gland(s), subtotal parathyroidectomy, or total parathyroidectomy with forearm autograft [American Thyroid Association Guidelines Task Force 2009]. However, in most individuals with MEN 2A, hyperparathyroidism is diagnosed many years after thyroidectomy. Individuals with biochemical evidence of primary hyperparathyroidism who have undergone prior thyroidectomy should have preoperative localization with excision of the localized hypertrophied parathyroid glands and forearm autotransplantation.Therapy with medications to control primary hyperparathyroidism should be considered in individuals with a high risk for surgical mortality, limited life expectancy, or persistent or recurrent primary hyperparathyroidism after one or more surgical attempts [American Thyroid Association Guidelines Task Force 2009].Prevention of Primary ManifestationsProphylactic thyroidectomy is the primary preventive measure for individuals with an identified germline RET mutation [Cohen & Moley 2003, American Thyroid Association Guidelines Task Force 2009]. Prophylactic thyroidectomy is safe for all age groups; however, the timing of the surgery is controversial [Moley et al 1998]. According to the consensus statement from the American Thyroid Association Guidelines Task Force, the age at which prophylactic thyroidectomy is performed can be guided by the codon position of the RET mutation (Table 4, Genotype-Phenotype Correlations) [American Thyroid Association Guidelines Task Force 2009]. However, these guidelines continue to be modified as more data become available. Table 4. Risk for Aggressive MTC Based on Genotype and Recommended InterventionsView in own windowATA ¹ Risk LevelMutations ^{2, 3Age of Prophylactic SurgeryAge to Begin Screening For PHEOFor HPTLevel D
(highest risk)p.Ala883Phe
p.Met918Thr
p.Val804Met+p.Glu805Lys 4p.Val804Met+p.Tyr806Cys 4p.Val804Met+p.Ser904Cys 4As soon as possible in 1st year of life8 yrsNALevel Cp.Cys634Arg/Gly/Phe/Ser/Trp/Tyr<5 yrs8 yrs8 yrsLevel Bp.Cys609Phe/Arg/Gly/Ser/Tyr
p.Cys611Arg/Gly/Phe/Ser/Trp/Tyr
p.Cys618Arg/Gly/Phe/Ser/Tyr
p.Cys620Arg/Gly/Phe/Ser/Trp/Tyr
p.Cys630Arg/Phe/Ser/Tyr
p.Asp631Tyr
p.633/9 bp dup
p.634/12 bp dup
p.Val804Met+p.Val778Ile 4Consider <5 yrs; may delay if criteria met 4Codon 630 mutation: 8 yrs
All others: 20 yrsCodon 630 mutation: 8 yrs
All others: 20 yrsLevel Ap.Arg321Gly
p.531/9 bp dup
p.532 dup
p.Cys515Ser
p.Gly533Cys
p.Arg600Gln
p.Lys603Glu
p.Tyr606Cys
p.635/insert ELCR;p.Thr636Pro
p.Lys666Glu
p.Glu768Asp
p.Asn777Ser
p.Leu790Phe
p.Val804Leu/Met
p.Gly819Lys
p.Arg833Cys
p.Arg844Gln
p.Arg866Trp
p.Ser891Ala
p.Arg912ProMay delay beyond age 5 yrs if criteria met 520 yrs20 yrsAdapted from American Thyroid Association Guidelines Task Force [2009]1. ATA = American Thyroid Association2. p.Ser649Leu and p.Tyr791Phe have been removed from this list as they were reclassified as polymorphisms [Erlic et al 2010].3. Mutation designations have not been edited by GeneReviews staff and may not be standard nomenclature.4. Mutations in cis on one allele 5. Criteria: normal annual basal and or stimulated serum calcitonin; normal annual neck ultrasound examination; family history of less aggressive MTC Thyroidectomy for C-cell hyperplasia, before progression to invasive MTC, may allow surgery to be limited to thyroidectomy with sparing of lymph nodes [Brandi et al 2001, Kahraman et al 2003]. For all individuals with a RET mutation who have not had a thyroidectomy, annual biochemical screening is recommended with immediate thyroidectomy if results are abnormal [Szinnai et al 2003]. Annual serum calcitonin screening [American Thyroid Association Guidelines Task Force 2009] should begin at age: Six months for children with MEN 2B;Three to five years for children with MEN 2A or FMTC. Caution should be used in interpreting calcitonin results for children younger than age three years, especially those younger than age six months [American Thyroid Association Guidelines Task Force 2009]. Prophylactic thyroidectomy is not routinely offered to at-risk individuals in whom the disorder has not been confirmed. Prevention of Secondary ComplicationsPrior to any surgery, the presence of a functioning pheochromocytoma should be excluded by appropriate biochemical screening in any individual with MEN 2A or MEN 2B. In a prospective study of at-risk family members with the disease-causing mutation, 8% had pheochromocytoma detected at the same time as MTC [Nguyen et al 2001]. If pheochromocytoma is detected, adrenalectomy should be performed before thyroidectomy to avoid intraoperative catecholamine crisis [Lee & Norton 2000]. SurveillanceMTC. Approximately 50% of individuals diagnosed with MTC who have undergone total thyroidectomy and neck nodal dissections have recurrent disease [Cohen & Moley 2003]. Furthermore, thyroid glands removed from individuals with a RET disease-causing mutation who had normal plasma calcitonin concentrations have been found to contain MTC [Skinner et al 1996]. Therefore, continued monitoring for residual or recurrent MTC is indicated after thyroidectomy, even if thyroidectomy is performed prior to biochemical evidence of disease. The screening protocol for MTC after prophylactic thyroidectomy is an annual measurement of serum calcitonin [American Thyroid Association Guidelines Task Force 2009]. More frequent follow up is recommended for those with residual disease.Hypoparathyroidism. All individuals who have undergone thyroidectomy and autotransplantation of the parathyroids need monitoring for possible hypoparathyroidism. Pheochromocytoma. For individuals whose initial screening results are negative for pheochromocytoma, annual biochemical screening is recommended, followed by MRI and/or CT if the biochemical results are abnormal [Pacak et al 2005, American Thyroid Association Guidelines Task Force 2009]. Women with MEN 2 should be screened for pheochromocytoma prior to a planned pregnancy, or as early as possible during an unplanned pregnancy [American Thyroid Association Guidelines Task Force 2009]. Other screening studies, such as scintigraphy or positron emission tomography, may be warranted in some individuals. MEN 2A. Annual biochemical screening beginning at age eight years has been recommended for individuals with mutations of codons 630 and 634 and at age 20 years for mutations in all other codons [American Thyroid Association Guidelines Task Force 2009]. FMTC. Screening as for MEN 2A is indicated, as not all families classified as FMTC are MTC-only [Moers et al 1996].MEN 2B. Annual screening should begin at age eight years [American Thyroid Association Guidelines Task Force 2009]. Parathyroid adenoma or hyperplasia. Annual biochemical screening is recommended for affected individuals who have not had parathyroidectomy and parathyroid autotransplantation. MEN 2A. Screening should start at age eight years for individuals with mutations of codons 630 and 634, and by age 20 years for individuals with other RET mutations [American Thyroid Association Guidelines Task Force 2009]. FMTC. Periodic screening should begin at age 20 years [American Thyroid Association Guidelines Task Force 2009]. MEN 2B. Screening is unnecessary as individuals with MEN 2B do not have an increased risk of hyperparathyroidism. Agents/Circumstances to AvoidDopamine D₂ receptor antagonists (e.g., metoclopramide and veralipride) and β-adrenergic receptor antagonists (β-blockers) have a high potential to cause an adverse reaction in individuals with pheochromocytoma. Other medications including monoamine oxidase inhibitors, sympathomimetics (e.g., ephedrine), and certain peptide and corticosteroid hormones may also cause complications; tricyclic antidepressants are inconsistent in causing adverse reactions [Eisenhofer et al 2007]. Evaluation of Relatives at RiskIdentification of individuals with germline RET gene disease-causing mutations. RET molecular genetic testing should be offered to probands with any of the MEN 2 subtypes and to all at-risk members of kindreds in which a germline RET mutation has been identified in an affected family member. American Society of Clinical Oncologists (ASCO) identifies MEN 2 as a Group 1 disorder, i.e., a well-defined hereditary cancer syndrome for which genetic testing is considered part of the standard management for at-risk family members [American Society of Clinical Oncology 2003]. MEN 2A. RET molecular genetic testing should be offered to at-risk children by age five years, since MTC has been documented in childhood [Lips 1998, Brandi et al 2001]. The finding of MTC in the thyroid of a 12-month-old with a MEN 2A-causing mutation in RET suggests that molecular genetic testing should be performed even earlier when possible [Machens et al 2004]. FMTC. Recommendations for families with known FMTC are the same as for MEN 2A. MEN 2B. RET molecular genetic testing should be performed as soon as possible after birth in all children known to be at risk [Brandi et al 2001]. In a child who does not have a family history of MEN 2B, RET molecular genetic testing should be performed as soon as the clinical diagnosis is suspected [Morrison & Nevin 1996]. Rarely, a germline RET mutation may not be detected in a family with a clinical diagnosis of MEN 2A or 2B, or FMTC. At-risk relatives should be periodically screened for MTC with neck ultrasound examination and basal and/or stimulated calcitonin measurements; for hyperparathyroidism with albumin-corrected calcium or ionized calcium; and for pheochromocytoma with measurement of plasma or 24-hour urine metanephrines and normetanephrines as appropriate [American Thyroid Association Guidelines Task Force 2009]. See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.Pregnancy Management Women with MEN 2 should be screened for pheochromocytoma prior to a planned pregnancy, or as early as possible during an unplanned pregnancy [American Thyroid Association Guidelines Task Force 2009].Therapies Under InvestigationAdenoviral vectors expressing a dominant-negative truncated form of RET, termed RET(DeltaTK), were able to induce apoptosis in MTC cells in vitro and also led to tumor regression in transgenic mice [Drosten et al 2004].Santoro et al [2004] reviewed the potential of tyrosine kinase inhibitors as therapeutic agents for MTC. In vitro studies using cells with mutant RET suggest therapeutic potential for RPI-1, a novel 2-indolinone Ret tyrosine kinase inhibitor [Cuccuru et al 2004]. Other inhibitors of tyrosine kinase, PP2 and genistein, have been shown to decrease proliferation of a human MTC cell line [Liu et al 2004]. Clinical trials of tyrosine kinase inhibitors, such as vandetanib (ZD6474), are currently underway. In a Phase II trial, 50% (15/30) of individuals with hereditary metastatic MTC who were treated with vandetanib experienced a partial response or stable disease [Wells et al 2012]. Tyrosine kinase inhibitors are promising potential treatments for patients with unresectable, locally advanced, or metastatic MTC. Search ClinicalTrials.gov for access to information on clinical studies for a wide range of diseases and conditions.}

Molecular GeneticsInformation in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED.Table A. Multiple Endocrine Neoplasia Type 2: Genes and DatabasesView in own windowGene SymbolChromosomal LocusProtein NameLocus SpecificHGMDRET10q11​.21Proto-oncogene tyrosine-protein kinase receptor retCatalogue of Somatic Mutations in Cancer (COSMIC)
ARUP Laboratories MEN2 Mutation Database
RET homepage - Mendelian genesRETData are compiled from the following standard references: gene symbol from HGNC; chromosomal locus, locus name, critical region, complementation group from OMIM; protein name from UniProt. For a description of databases (Locus Specific, HGMD) to which links are provided, click here.Table B. OMIM Entries for Multiple Endocrine Neoplasia Type 2 (View All in OMIM) View in own window 155240THYROID CARCINOMA, FAMILIAL MEDULLARY; MTC 162300MULTIPLE ENDOCRINE NEOPLASIA, TYPE IIB; MEN2B 164761REARRANGED DURING TRANSFECTION PROTOONCOGENE; RET 171400MULTIPLE ENDOCRINE NEOPLASIA, TYPE IIA; MEN2ANormal allelic variants. The RET proto-oncogene is composed of 21 exons over 55 kb of genomic sequence. Normal allelic variants as well as variants of uncertain significance have been described. See Table A for a database of normal, uncertain, and pathologic RET variants [Margraf et al 2009]. It is speculated that some rare variants (e.g., p.Val648Ile) may modify the phenotype when inherited with a pathogenic mutation [Nunes et al 2002]. Evidence suggests that other rare allelic variants may be predisposition factors. For example, p.Gly691Ser and p.Ser904Ser may be low-penetrance risk factors for development of MTC [Elisei et al 2004, Robledo et al 2003] and may predispose individuals with a pathologic mutation to an earlier age of onset of MEN 2A [Gil et al 2002, Robledo et al 2003, Cardot-Bauters et al 2008]; however, this finding was not replicated in a larger study [Lesueur et al 2006]. The p.Ser836Ser variant has been associated with an increased risk for nonfamilial MTC in at least two studies [Gimm et al 1999, Ruiz et al 2001] but not in another [Berard et al 2004]. A meta-analysis of six allelic variants found a modest nonfamilial MTC association with p.Ser836Ser and a strong association with the promoter polymorphism IVS1-126G>T [Figlioli et al 2012].The variants p.Ser649Leu and p.Tyr791Phe were recently reclassified as non-pathogenic, although whether they act as modifiers of risk is unknown [Erlic et al 2010]. Pathologic allelic variants. The major disease-causing mutations are non-conservative substitutions located in one of six cysteine codons in the extracellular domain of the encoded protein. They include codons 609, 611, 618, and 620 in exon 10 and codons 630 and 634 in exon 11 [Takahashi et al 1998]. All of these variants have been identified in families with MEN 2A and some have been identified in families with FMTC. Mutations in these sites have been detected in 98% of families with MEN 2A [Eng et al 1996]. See Table A for a database of RET variants and mutations [Margraf et al 2009]. Approximately 95% of all individuals with the MEN 2B phenotype have a single point mutation in the tyrosine kinase domain of RET at codon 918 in exon 16, which substitutes a threonine for methionine [Eng et al 1996]. A second point mutation at codon 883 has been found in 2%-3% of individuals with MEN 2B [Gimm et al 1997, Smith et al 1997]. Tandem RET mutations of codons 805, 806, and 904 in cis configuration with the p.Val804Met mutation have also been reported in individuals with MEN 2B [Miyauchi et al 1999, Menko et al 2002, Cranston et al 2006, American Thyroid Association Guidelines Task Force 2009]. In addition to the mutations of the cysteine residues in exons 10 and 11 that have been found in families with MEN 2A, mutations in codons 631, 768, 790, 804, 844, 891, and others in exons 5, 8, 10, 11, and 13 to 16 have also been identified in a small number of families [Hofstra et al 1997, Berndt et al 1998, American Thyroid Association Guidelines Task Force 2009]. A mutation at codon 603 was reported in one family and appeared to be associated with both MTC and papillary thyroid cancer [Rey et al 2001]. The mutation p.Arg912Pro appeared to be associated with FMTC in two families [Jimenez et al 2004b]. Duplication mutations have been reported in four families [Höppner & Ritter 1997, Höppner et al 1998, Pigny et al 1999, Niccoli-Sire et al 2003]. Rare families have two mutations in cis configuration, for example, alteration of both codons 634 and 635 in one family with MEN 2A; alteration of both codons 804 and 844 in one family with FMTC [Bartsch et al 2000]; and alteration of codons 804 and 806 in an individual with MEN 2B [Miyauchi et al 1999].Normal gene product. RET produces a receptor tyrosine kinase with extracellular, transmembrane, and intracellular domains. The extracellular domain consists of a calcium-binding cadherin-like region and a cysteine-rich region. The encoded protein plays a role in signal transduction by interaction with the glial-derived neurotropic factor (GDNF) family of ligands: GDNF, neurturin, persephin, and artemin. Ligand interaction is via the ligand-binding GDNF family receptors (GFRα) to which RET protein binds the encoded protein complexes. Formation of a complex containing two RET protein molecules leads to RET autophosphorylation and intracellular signaling whereby phosphorylated tyrosines become docking sites for intracellular signaling proteins [Santoro et al 2004]. The RET tyrosine kinase catalytic core, which is located in the intracellular domain, interacts with the docking protein FRS2 and causes downstream activation of the mitogen-activated protein (MAP) kinase signaling cascade [Manié et al 2001]. Normal tissues contain transcripts of several lengths [Takaya et al 1996]. Abnormal gene product. Mutations in codons in the cysteine-rich extracellular domain (609, 611, 618, 620, and 634) cause ligand-independent RET dimerization, leading to constitutive activation (i.e., gain of function) of tyrosine kinase [Takahashi et al 1998]. The disease-causing point mutation codon 918 that causes 95% of the MEN 2B phenotype lies within the catalytic core of the tyrosine kinase and causes a constitutive activation (i.e., gain of function) of the RET kinase in its monomeric state, independent of the normal ligand-binding and dimerization steps [Takahashi et al 1998]. In contrast to the activating mutations in MEN 2, mutations that cause Hirschsprung disease (HSCR) result in a decrease in the transforming activity of RET [Iwashita et al 1996]. For families in which MEN 2A and HSCR cosegregate, models to explain how the same mutation can cause gain of function and loss of function have been proposed [Takahashi et al 1999].