RET mutation Tyr791Phe: the genetic cause of different diseases derived from neural crest

Incidence of medullary thyroid carcinoma and Hirschsprung disease based on the cosmos database

PURPOSE

Multiple endocrine neoplasia Type 2A (MEN2A) can occur with Hirschsprung disease (HD) due to mutation in the RET proto-oncogene, with the majority developing medullary thyroid carcinoma (MTC). Given the comorbidity, many parents have contacted us to share concerns and unfortunate experiences about the prevalence rates of MEN2A/MTC in patients with HD. The aim is to determine the prevalence rate of patients with HD and MEN2A or medullary thyroid carcinoma, respectively.

METHODS

This is a cross-sectional study of the COSMOS database from January 01, 2017, to March 08, 2023. The database was searched for patients diagnosed with MEN2A, MTC, and HD. IRB exemption was provided (COMIRB #23-0526).

RESULTS

The database contained 183,993,122 patients from 198 contributing organizations. The prevalence of HD and MEN2A was 0.00002%, and for HD and MTC was 0.000009%. One in 66 patients (1.5%) with MEN2A also had HD. One in 319 patients (0.3%) in the HD group had MEN2A. One in 839 patients (0.1%) within the HD population had MTC.

CONCLUSION

The prevalence of MTC and HD or MEN2A and HD in the study population was low. Considering that almost all MEN2A patients have a positive family history, this data does not support the general genetic testing of HD patients.

Cytochrome P450 and flavin-containing monooxygenase enzymes are responsible for differential oxidation of the anti-thyroid-cancer drug vandetanib by human and rat hepatic microsomal systems

We studied the in vitro metabolism of the anti-thyroid-cancer drug vandetanib in a rat animal model and demonstrated that N-desmethylvandetanib and vandetanib N-oxide are formed by NADPH- or NADH-mediated reactions catalyzed by rat hepatic microsomes and pure biotransformation enzymes. In addition to the structural characterization of vandetanib metabolites, individual rat enzymes [cytochrome P450 (CYP) and flavin-containing monooxygenase (FMO)] capable of oxidizing vandetanib were identified. Generation of N-desmethylvandetanib, but not that of vandetanib N-oxide, was attenuated by CYP3A and 2C inhibitors while inhibition of FMO decreased formation of vandetanib N-oxide. These results indicate that liver microsomal CYP2C/3A and FMO1 are major enzymes participating in the formation of N-desmethylvandetanib and vandetanib N-oxide, respectively. Rat recombinant CYP2C11 > >3A1 > 3A2 > 1A1 > 1A2 > 2D1 > 2D2 were effective in catalyzing the formation of N-desmethylvandetanib. Results of the present study explain differences between the CYP- and FMO-catalyzed vandetanib oxidation in rat and human liver reported previously and the enzymatic mechanisms underlying this phenomenon.

Identification of Human Enzymes Oxidizing the Anti-Thyroid-Cancer Drug Vandetanib and Explanation of the High Efficiency of Cytochrome P450 3A4 in its Oxidation

The metabolism of vandetanib, a tyrosine kinase inhibitor used for treatment of symptomatic/progressive medullary thyroid cancer, was studied using human hepatic microsomes, recombinant cytochromes P450 (CYPs) and flavin-containing monooxygenases (FMOs). The role of CYPs and FMOs in the microsomal metabolism of vandetanib to N-desmethylvandetanib and vandetanib-N-oxide was investigated by examining the effects of CYP/FMO inhibitors and by correlating CYP-/FMO-catalytic activities in each microsomal sample with the amounts of N-desmethylvandetanib/vandetanib-N-oxide formed by these samples. CYP3A4/FMO-activities significantly correlated with the formation of N-desmethylvandetanib/ vandetanib-N-oxide. Based on these studies, most of the vandetanib metabolism was attributed to N-desmethylvandetanib/vandetanib-N-oxide to CYP3A4/FMO3. Recombinant CYP3A4 was most efficient to form N-desmethylvandetanib, while FMO1/FMO3 generated N-oxide. Cytochrome b₅ stimulated the CYP3A4-catalyzed formation of N-desmethylvandetanib, which is of great importance because CYP3A4 is not only most efficient in generating N-desmethylvandetanib, but also most significant due to its high expression in human liver. Molecular modeling indicated that binding of more than one molecule of vandetanib into the CYP3A4-active center can be responsible for the high efficiency of CYP3A4 N-demethylating vandetanib. Indeed, the CYP3A4-mediated reaction exhibits kinetics of positive cooperativity and this corresponded to the in silico model, where two vandetanib molecules were found in CYP3A4-active center.

Long-term follow-up of RET Y791F carriers in Denmark 1994-2017: A National Cohort Study

BACKGROUND AND OBJECTIVES

Recently, a comprehensive study presented evidence that a long-disputed REarranged during Transfection (RET) variant, RET Y791F, should be classified as nonpathogenic. In spite of this, several subsequently published papers, including the revised American Thyroid Association guidelines for medullary thyroid carcinoma, refer to the variant as pathogenic. This study presents data from a unique national Danish cohort of RET Y791F carriers who have been followed by watchful waiting instead of being subjected to early thyroidectomy, to determine if any carrier shows evidence of multiple endocrine neoplasia 2A (MEN2A) at long-term follow-up.

METHODS

A national cohort of all patients tested for RET mutations in Denmark from September 1994 to October 2017 was searched for carriers of RET Y791F. Medical records and laboratory reports of carriers were reviewed for signs of MEN2A at latest follow-up (medullary thyroid carcinoma, primary hyperparathyroidism, pheochromocytoma, cutaneous lichen amyloidosis, or Hirschsprung's disease).

RESULTS

In total, twenty RET Y791F-carriers were identified, none of whom showed any evidence of MEN2A, despite an age range from 7 to 87 years.

CONCLUSIONS

Our national cohort study of all Danish RET Y791F carriers substantiates the claim that the RET Y791F variant is nonpathogenic.

Questioning the pathogenic role of the pTyr791Phe mutation of the RET proto-oncogene: Insight from a case report

The pTyr791Phe mutation of the RET proto-oncogene is associated with a low penetrance of medullar thyroid carcinoma (MTC). Thus, there is a lack in guidelines on management of these patients presenting without a thyroid disease.

CLINICAL CASE

A 27-year-old woman presented with a history of severe hypertension, paroxysmal tachycardia, diaphoresis and headaches. Twenty-four-hour urinary norepinephrine and normetanephrine levels were exclusively up to 20 times the normal limit. CT-scan and MRI found a 35-mm diameter right adrenal tumor, highly intense in T2- and hypo-intense in T1-weighted image, enhanced after gadolinium injection. After alpha-adrenergic blocker treatment, a surgical resection of the tumor was performed; this latter proved to be a pheochromocytoma. Genetic screening only revealed a germline pTyr791Phe mutation of the RET proto-oncogene. However, the patient showed no evidence of MEN2: basal calcitonin was normal and calcium infusion test was negative. Thyroid ultrasound revealed a TIRADS 3 nodule with benign cytology. Total thyroidectomy was suggested but withheld due to the patient's refusal and a close follow-up was decided.

CONCLUSION

This rare case of pTyr791Phe mutation-related pheochromocytoma without evidence of MTC questions the indication for prophylactic thyroidectomy in mutation carriers, as recent data challenges its pathogenicity.

Hereditary Medullary Thyroid Cancer Genotype-Phenotype Correlation

During the last two decades, there has been a marked expansion of our knowledge of both the basic and clinical aspects of multiple endocrine neoplasia type 2 (MEN2). There are two clinically distinct types of MEN2 syndrome, termed MEN2A and MEN2B. Within MEN2A, there are four variants: (i) classical MEN2A, represented by the uniform presence of MTC and the less frequent occurrence of pheochromocytoma, or primary hyperparathyroidism, or both; (ii) MEN2A with cutaneous lichen amyloidosis; (iii) MEN2A with Hirschsprung's disease; and (iv) familial medullary thyroid carcinoma (FMTC), i.e., families or individuals with only MTC. MEN2B is associated with MTC, pheochromocytoma, and mucosal neuromas. Hereditary MTC is caused by autosomal dominant gain of function mutations in the RET proto-oncogene. Specific RET mutations may suggest a predilection toward a particular phenotype and clinical course with a strong genotype-phenotype correlation. Based upon these genotype-phenotype correlations, RET mutations are now stratified into three risk levels, i.e., highest, high, and moderate risk, based on the penetrance and aggressiveness of the MTC. Children in the highest risk category should undergo thyroidectomy in their first year of life, and perhaps even in their first months of life. Children in the high-risk category should have ultrasound of the neck and calcitonin (CTN) measurement performed prior to thyroidectomy. Thyroidectomy should typically be performed at the age of 5 or earlier, depending on the presence of elevated serum CTN levels. However, heterogeneity in disease expression and progression within these groups varies considerably. To personalize disease management, the decision regarding the age of prophylactic thyroidectomy is no longer based upon genotype alone but is currently driven by additional clinical data, the most important being serum CTN levels; specifically, the decision to perform thyroidectomy should err on the safe side if the CTN level is elevated but below 30 pg/ml, especially in the moderate risk group. Personalized management also includes decisions about the best age to begin biochemical screening for pheochromocytoma and primary hyperparathyroidism.

The association between Hirschsprung's disease and multiple endocrine neoplasia type 2a: a systematic review

PURPOSE

The co-occurrence of Hirschsprung's disease (HSCR) and multiple endocrine neoplasia type 2 (MEN2) is a relatively rare event. The basis for this association is the presence of a "Janus" mutation in the RET proto-oncogene--a mutation that acts simultaneously as both a gain-in-function and a loss-of-function mutation. To date, four mutations in the exon 10 region of RET that are known to cause MEN2A have been implicated in this association: C620, C618, C611 and C609. We performed a systematic review of the published literature on this association to determine its incidence, the prevalence and phenotype of HSCR associated with the 4 RET mutations mentioned above.

METHODS

A systematic literature-based search for relevant articles was conducted using three online databases. After exclusion of ineligible publications, we recorded data on all patients with a diagnosis of HSCR or MEN2A with a "Janus" RET mutation, as well as those who carried the mutation but were unaffected. Statistical analysis was performed using SPSS.

RESULTS

The literature search yielded 885 publications, of which 36 articles, incorporating data on 341 individuals, were eligible for inclusion in the final analysis. Co-occurrence of HSCR and MEN2A was recorded in 84 cases (24.6 %). HSCR occurred alone in 64 carriers of a "Janus" mutation (18.8 %) and MEN2A occurred in isolation in 173 cases (50.7 %). Twenty individuals (5.9 %) were found to carry a "Janus" mutation after screening on the basis of family history but were unaffected by either MEN2A or HSCR. The most common mutation recorded was the C620 mutation [114 cases (48.1 %)]. There was a relatively high incidence of long-segment aganglionosis (29.3 %) and total colonic aganglionosis (17.3 %) in this cohort. This trend was particularly notable in those with C620 mutations, only 33 % of whom had short-segment disease.

CONCLUSION

While the overall incidence of HSCR co-occurring with MEN2A is low, both conditions occur with a relatively high frequency in families with a RET mutation at exon 10. The proportion of cases of long-segment HSCR and total colonic aganglionosis is higher than that in the general population with HSCR in those with C620 and C618 mutations. These findings reinforce the importance of RET mutation testing in HSCR when a family history of either HSCR or MEN2 is present. In families with MEN2A and known exon 10 RET mutations, the threshold for investigation for HSCR in those with gastrointestinal symptoms should be very low. High-quality prospective longitudinal studies of large HSCR populations are required to shed greater light on this rare but important phenomenon.

Prevalence by age and predictors of medullary thyroid cancer in patients with lower risk germline RET proto-oncogene mutations

BACKGROUND

Age-related risk of medullary thyroid carcinoma (MTC) development in presymptomatic carriers of lower risk germline RET mutations is uncertain; such data may aid counseling patients regarding timing of thyroidectomy.

METHODS

From an institutional database and an exhaustive literature review, we identified 679 patients with American Thyroid Association (ATA) level A or B mutations who were identified because of family screening (index cases of MTC were excluded to minimize selection bias). We evaluated age at thyroidectomy or last evaluation if no thyroidectomy, preoperative calcitonin level (elevated or not), the mutated codon, and outcome (MTC vs. no MTC after thyroidectomy or no clinical evidence of MTC if thyroid intact). Data were used to estimate the cumulative prevalence of MTC and/or assess likelihood of MTC stratified by codon. After exclusion of cases with missing data or small representation, 503 patients with mutations in codons 533, 609, 611, 618, 620, 791, and 804 were analyzed.

RESULTS

236 patients had MTC. Cumulative prevalence and median time to MTC varied by codon and within ATA risk levels (p<0.0001). Patients with a codon 620 mutation were 2.8-6.9 times more likely to have MTC than other level B mutation carriers, and 5.1-21.7 times more likely than level A mutation carriers included in our focus population. The youngest median time to MTC was 19 years for codon 620 and the oldest was 56 years for codon 611. Cumulative prevalence of MTC by age 20 was 10% or lower for codons 533, 609, 611, 791, and 804. By age 50, it ranged from 18% for codon 791 to 95% for codon 620. An elevated preoperative calcitonin level strongly predicted MTC on final pathology, though false-negative rates varied by codon (p<0.0001). Positive predictive values ranged from 76% to 100% by codon with an overall positive predictive value of 87% across codons.

CONCLUSIONS

This study offers a better understanding of the age-related development of MTC in lower risk RET mutation carriers, provides evidence of further distinctions between lower risk mutations within ATA subgroups, and clarifies the clinical significance of codon 791 mutations. The data support individualized "codon-based" management approaches coupled with clinical data such as calcitonin levels.

Integrative genetic characterization and phenotype correlations in pheochromocytoma and paraganglioma tumours

BACKGROUND

About 60% of Pheochromocytoma (PCC) and Paraganglioma (PGL) patients have either germline or somatic mutations in one of the 12 proposed disease causing genes; SDHA, SDHB, SDHC, SDHD, SDHAF2, VHL, EPAS1, RET, NF1, TMEM127, MAX and H-RAS. Selective screening for germline mutations is routinely performed in clinical management of these diseases. Testing for somatic alterations is not performed on a regular basis because of limitations in interpreting the results.

AIM

The purpose of the study was to investigate genetic events and phenotype correlations in a large cohort of PCC and PGL tumours.

METHODS

A total of 101 tumours from 89 patients with PCC and PGL were re-sequenced for a panel of 10 disease causing genes using automated Sanger sequencing. Selected samples were analysed with Multiplex Ligation-dependent Probe Amplification and/or SNParray.

RESULTS

Pathogenic genetic variants were found in tumours from 33 individual patients (37%), 14 (16%) were discovered in constitutional DNA and 16 (18%) were confirmed as somatic. Loss of heterozygosity (LOH) was observed in 1/1 SDHB, 11/11 VHL and 3/3 NF1-associated tumours. In patients with somatic mutations there were no recurrences in contrast to carriers of germline mutations (P = 0.022). SDHx/VHL/EPAS1 associated cases had higher norepinephrine output (P = 0.03) and lower epinephrine output (P<0.001) compared to RET/NF1/H-RAS cases.

CONCLUSION

Somatic mutations are frequent events in PCC and PGL tumours. Tumour genotype may be further investigated as prognostic factors in these diseases. Growing evidence suggest that analysis of tumour DNA could have an impact on the management of these patients.

Testing new susceptibility genes in the cohort of apparently sporadic phaeochromocytoma/paraganglioma patients with clinical characteristics of hereditary syndromes

BACKGROUND

Phaeochromocytoma (PCC) and paraganglioma (PGL) can occur sporadically or as a part of familial cancer syndromes. Red flags of hereditary syndromes are young age and multifocal tumours. We hypothesized that such patients are candidates for further molecular diagnosis in case of normal results in 'classical' genes.

MATERIAL AND METHODS

We selected patients with PCC/PGL under the age of 40 and/or with multiple tumours. First, we tested the genes RET, VHL, NF1, SDHB, SDHC and SDHD. Patients without mutations in these genes were tested for mutations in MAX, TMEM127 and SDHAF2.

RESULTS

In 153 patients included, mutations were detected in the classical genes in 72 patients (47%) [RET-22 (14%), VHL-13 (9%), NF1-3 (2%), SDHB-13 (9%), SDHC-3 (2%), SDHD-16 (11%), SDHB large deletions- 2 (1%)]. One patient with MAXc.223C>T (p.R75X) mutation was detected. It was a male with bilateral, metachronous phaeochromocytomas diagnosed in 36 and 40 years of age. Remarkably, he showed in the period before the MAX gene was detected, a RET p. Y791F variant. During 10-year follow-up, we did not find any thyroid abnormalities. LOH examination of tumour tissue showed somatic loss of the wild-type allele of MAX.

CONCLUSION

Analysis of the MAX gene should be performed in selected patients, especially those with bilateral adrenal phaeochromocytoma in whom mutations of the classical genes are absent. Our study provides with further support that Y791F RET is a polymorphism.

Comprehensive analysis of RET gene should be performed in patients with multiple endocrine neoplasia type 2 (MEN 2) syndrome and no apparent genotype-phenotype correlation: an appraisal of p.Y791F and p.C634Y RET mutations in five unrelated Brazilian families

BACKGROUND

We previously identified a four-generation family with medullary thyroid cancer (MTC) and a germline p.Y791F RET mutation whose cancer lacked a strong genotype-phenotype correlation. The entire gene coding region of the RET gene should be sequenced when genotype-phenotype discrepancies are observed in patients with multiple endocrine neoplasia type 2 (MEN 2), even if a RET hotspot mutation has been identified.

METHODS

A new genetic test was performed in the index case of this family with the p.Y791F RET germline mutation. The entire coding region of the RET gene was investigated by direct sequencing of PCR products. Once a mutation was identified, the target exon was sequenced in all at-risk relatives.

RESULTS

An additional p.C634Y germline mutation in the RET gene was identified in the reported family. The double mutation occurred in cis and segregated with the phenotype. Through the Brazilian Genetic Screening Program developed at our institution, we additionally report the combination of these two mutations (p.C634Y/p.Y791F) in the RET gene in four other unrelated families. The overall penetrance of MTC and pheochromocytoma in patients with the p.C634Y/p.Y791F mutations was 79% and 13%, respectively.

CONCLUSION

Our data emphasises that a comprehensive analysis of the RET gene may reveal multiple germline mutations in MEN 2 patients who exhibit an atypical clinical course of the disease.

Next-generation sequencing in the clinical genetic screening of patients with pheochromocytoma and paraganglioma

BACKGROUND

Recent findings have shown that up to 60% of pheochromocytomas (PCCs) and paragangliomas (PGLs) are caused by germline or somatic mutations in one of the 11 hitherto known susceptibility genes: SDHA, SDHB, SDHC, SDHD, SDHAF2, VHL, HIF2A (EPAS1), RET, NF1, TMEM127 and MAX. This list of genes is constantly growing and the 11 genes together consist of 144 exons. A genetic screening test is extensively time consuming and expensive. Hence, we introduce next-generation sequencing (NGS) as a time-efficient and cost-effective alternative.

METHODS

Tumour lesions from three patients with apparently sporadic PCC were subjected to whole exome sequencing utilizing Agilent Sureselect target enrichment system and Illumina Hi seq platform. Bioinformatics analysis was performed in-house using commercially available software. Variants in PCC and PGL susceptibility genes were identified.

RESULTS

We have identified 16 unique genetic variants in PCC susceptibility loci in three different PCC, spending less than a 30-min hands-on, in-house time. Two patients had one unique variant each that was classified as probably and possibly pathogenic: NF1 Arg304Ter and RET Tyr791Phe. The RET variant was verified by Sanger sequencing.

CONCLUSIONS

NGS can serve as a fast and cost-effective method in the clinical genetic screening of PCC. The bioinformatics analysis may be performed without expert skills. We identified process optimization, characterization of unknown variants and determination of additive effects of multiple variants as key issues to be addressed by future studies.

Hirschsprung's disease and medullary thyroid carcinoma: 15-year experience with molecular genetic screening of the RET proto-oncogene

PURPOSE

Inactivating germline mutations in the RET proto-oncogene are the major genetic cause of Hirschsprung's disease (HD). In some cases, HD can be associated with medullary thyroid carcinoma (MTC) that is commonly caused by activating RET mutations.

METHODS

The retrospective and prospective genetic analyses of 157 patients with HD operated on between December 1979 and June 2011 were carried out. DNA was isolated from peripheral leukocytes. HD patients and family members were tested for RET mutations by direct sequencing and single-strand conformation polymorphism methods.

RESULTS

RET mutations were detected in 16 patients (10%). Association with MTC was found in two families, other eight families had a mutation with potentially high risk of MTC development and four novel mutations were detected. Total colonic aganglionosis was noted to have a high mutation detection rate (40%). Three patients underwent total thyroidectomy (two had clinical manifestation of MTC, one C-cell hyperplasia).

CONCLUSION

Results show the benefit of systematic RET mutation screening in HD patients in order to identify the risk of MTC in the preclinical stage of the disease. All patients should be tested for RET mutations at least in exon 10, and now additionally in exon 11 and 13, as well.

Molecular mechanisms of RET receptor-mediated oncogenesis in multiple endocrine neoplasia 2

Multiple endocrine neoplasia type 2 is an inherited cancer syndrome characterized by tumors of thyroid and adrenal tissues. Germline mutations of the REarranged during Transfection (RET) proto-oncogene, leading to its unregulated activation, are the underlying cause of this disease. Multiple endocrine neoplasia type 2 has been a model in clinical cancer genetics, demonstrating how knowledge of the genetic basis can shape the diagnosis and treatment of the disease. Here, we discuss the nature and effects of the most common recurrent mutations of RET found in multiple endocrine neoplasia type 2. Current understanding of the molecular mechanisms of RET mutations and how they alter the structure and function of the RET protein leading to its aberrant activation, and the effects on RET localization and signaling are described.

Genotype-phenotype correlation in multiple endocrine neoplasia type 2

Multiple endocrine neoplasia type 2 is an autosomal-dominant hereditary cancer syndrome caused by missense gain-of-function mutations of the rearranged during transfection proto-oncogene, which encodes the receptor tyrosine kinase, on chromosome 10. It has a strong penetrance of medullary thyroid carcinomas and can be associated with bilateral pheochromocytoma and primary hyperparathyroidism. Multiple endocrine neoplasia type 2 is divided into three varieties depending on its clinical features: multiple endocrine neoplasia type 2A, multiple endocrine neoplasia type 2B, and familial medullary thyroid carcinoma. The specific rearranged during transfection mutation may suggest a predilection toward a particular phenotype and clinical course of medullary thyroid carcinoma, with strong genotype-phenotype correlations. Offering rearranged during transfection testing is the best practice for the clinical management of patients at risk of developing multiple endocrine neoplasia type 2, and multiple endocrine neoplasia type 2 has become a classic model for the integration of molecular medicine into patient care. Recommendations on the timing of prophylactic thyroidectomy and extent of surgery are based on the classification of rearranged during transfection mutations into risk levels according to genotype-phenotype correlations. Earlier identification of patients with hereditary medullary thyroid carcinoma can change the presentation from clinical tumor to preclinical disease, resulting in a high cure rate of affected patients and a much better prognoses.