Distinct clinical phenotypes in a family with a novel truncating MEN1 frameshift mutation.

BACKGROUND: MEN1 mutations can inactivate or disrupt menin function and are leading to multiple endocrine neoplasia type 1, a rare heritable tumor syndrome. CASE PRESENTATION: We report on a MEN1 family with a novel heterozygous germline mutation, c.674delG; p.Gly225Aspfs*56 in exon 4 of the MEN1 gene. Diagnosis and clinical phenotyping of MEN1 was established by laboratory tests, ultrasound, biopsy, MRI imaging and endosonography. The clinical course of the disease was followed in the index patient and her family members for eight years. The mutation was associated with distinct clinical phenotypes in the index patient and three family members harboring p.Gly225Aspfs*56. Family members affected showed primary hyperparathyroidism but variable patterns of associated endocrine tumors, adrenal cortical adenomas, prolactinoma, multifocal pancreatic neuroendocrine tumors, insulinoma and nonsecretory neuroendocrine tumors of the pancreas. The mutation c.674delG; p.Gly225Aspfs*56 leads to a frameshift from codon 225 with early truncation of the menin protein. In silico analysis predicts loss of multiple protein-menin interactions in p.Gly225Aspfs*56, potentially rendering menin insufficient to control cell division and replication. However, no aggressive neuroendocrine tumors were observed in the follow-up of this family. CONCLUSIONS: We report a novel heterozygous MEN1 frameshift mutation, potentially causing (at least partial) inactivation of menin tumor suppression potential but lacking a genotype-phenotype correlation. Our study highlights the importance of personalized care with appropriate testing and counseling in MEN1 families.

Clinical relevance of RET variants G691S, L769L, S836S and S904S to sporadic medullary thyroid cancer.

BACKGROUND: Based on reports of higher frequencies among patients with sporadic medullary thyroid cancer (MTC) relative to external controls, the RET (REarranged during Transfection) variants G691S, L767L, S836S and S904S have been considered disease modifiers, suggesting greater lifetime risks of MTC. Other studies, employing different external controls, failed to confirm this association. Using a complementary approach, this study aimed at exploring differences in clinico-pathological characteristics among patients with sporadic MTC carrying no (wildtype), one (heterozygotes) or both (homozygotes) homologue RET variants in the germline, with wildtype cases acting as internal controls. METHODS: Included in this investigation were 150 patients with complete genetic information on G691S, L769L, S836S and S904S RET alleles operated on for sporadic MTC at a tertiary referral centre. RESULTS: Not one statistically significant dose-response relationship was identified between any RET variant (wildtype vs RET heterozygotes vs homologue RET homozygotes) and patient age at MTC diagnosis, gender, primary tumour size, extrathyroidal extension, numbers of involved and removed lymph nodes, or distant metastasis. L769L and S836S homozygotes, unlike G691S and S904S homozygotes, were either rare or absent, limiting the analyses to comparisons of heterozygosity versus wildtype. On time-to-event analysis, G691S, L769L, S836S or S904S carriers and noncarriers developed MTC at similar rates. CONCLUSIONS: In carriers and noncarriers of the RET variants G691S, L767L, S836S and S904S, sporadic MTC appeared clinically and pathologically indistinguishable. This observation, along with the inconclusive evidence of previous association studies, calls for larger longitudinal association studies with age- and sex-matched external controls and additional functional studies of RET biology.

Change in the spectrum of RET mutations diagnosed between 1994 and 2006.

Medullary thyroid carcinoma (MTC) is a rare calcitonin producing tumor. About 70-75% of patients with MTC have sporadic disease while the others suffer from hereditary MTC. Hereditary MTC is divided into three clinical subtypes: multiple endocrine neoplasia (MEN) type 2A is characterized by MTC, pheochromocytoma and primary hyperparathyroidism. MEN 2B is characterized by aggressive MTC, pheochromocytoma, marfanoid habitus and the presence of distinctive mucosal neuromas on the tongue, lips and subconjunctival areas as well as ganglioneuromatosis of the gastrointestinal tract. The third clinical subtype of inherited MTC, familial MTC, is defined as the presence of MTC in families without evidence of adrenal or parathyroid gland involvement. Hereditary MTC is caused by autosomal dominant gain-of-function mutations in the RET proto-oncogene. The first RET germline mutations were identified in 1993 in patients with MEN 2A and FMTC. Initially a codon 634 (exon 11) mutation was found in approximately 85% of patients with MEN 2A, and germline mutations in FMTC kindreds were more equally distributed throughout the RET proto-onocogene. In about 5% of families in these earlier series, mutations did not reside in exons 10 and 11. We now report a change in the spectrum of mutations detected in the RET proto-oncogene in patients with hereditary MTC from the 'classical' mutation at codon 634 in exon 11 (level 2) to more cases with mutations in the exons 13-15 (level 1) and less aggressive disease. In our series 38.9% of mutations were level 1 mutations, 54.4% level 2, and 5.6% level 3 mutations.

Multiple endocrine neoplasia type 1 associated with a new germline Men1 mutation in a family with atypical tumor phenotype.

BACKGROUND: Multiple endocrine neoplasia type 1 (MEN1) is an autosomal-dominant hereditary disorder associated with the development of endocrine tumors due to reduced expression of the tumor suppressor protein menin. Recent studies indicate a general role of menin in carcinogenesis, affecting the prevalence and clinical course of common non-endocrine tumors such as breast cancer, hepatocellular carcinoma and melanoma. Here we report a new germline missense mutation of Men1 in a German family with atypical tumor phenotype over three generations. Based on the type of mutation, we discuss possible changes in menin function leading to atypical tumorigenesis and present the clinical significance of such findings. CASE PRESENTATION: A German family with a history of primary hyperparathyroidism presented to our Hospital for further evaluation. Members of the family demonstrated many different atypical tumors, such as renal cell carcinoma, papillary thyroid cancer and prostate cancer. DNA sequencing from peripheral blood revealed a novel mutation: Ser38Cys [TCC>TGC] in exon 2, codon 38 of Men1. This novel mutation is located in a region of menin which is responsible for interactions with the transcription factor JunD. This factor has recently been associated with prostate cancer. DNA sequencing of two of the atypical tumors (prostate cancer, papillary thyroid cancer) did not reveal a loss of heterozygosity, indicating an impact on menin expression and function in the heterozygous state, in line with results in +/-Men1 mutant mice developing prostate cancer. CONCLUSION: The results and clinical course of disease in this case indicate the potential role of menin in the development of non-endocrine or atypical-endocrine tumors in MEN1 patients. Further investigations are needed to clarify both the general role of menin and the importance of specific mutations in carcinogenesis. Nevertheless, in families with uncommon manifestations of the syndrome early diagnostic adjustments should be considered.

Coincidence of multiple endocrine neoplasia types 1 and 2: mutations in the RET protooncogene and MEN1 tumor suppressor gene in a family presenting with recurrent primary hyperparathyroidism.

CONTEXT: Primary hyperparathyroidism (HPT) presents as a part of inherited syndromes such as multiple endocrine neoplasia (MEN) types 1 and 2. In patients with MEN1, parathyroid hyperplasia or multiple adenomas occur in approximately 90-95%. MEN2A-related HPT is characterized by a mild hypercalcemia, which is mostly asymptomatic. OBJECTIVE: Here we present a family with coexistence of MEN1 gene mutation and RET mutation. RESULTS: Six family members carrying MEN1 gene mutation IVS5 + 1G>A only, one family member with RET mutation Y791F, and three family members with both MEN1 gene and RET mutation were studied. The key to diagnosis was recurrent HPT in a young male carrying RET mutation Y791F, a mutation not likely to give rise to recurrent HPT. CONCLUSION: MEN1 gene mutation and RET codon 791 mutation in the same patient did not affect the typical phenotype of MEN1 or MEN2, and also the course of diseases seems to be unchanged. The reason may be that both mutations, although contributing to tumor pathogenesis, do not interact and induce a worsening of the cancer syndromes.

Prevalence and clinical spectrum of nonsecretory medullary thyroid carcinoma in a series of 839 patients with sporadic medullary thyroid carcinoma.

BACKGROUND: Medullary thyroid carcinoma (MTC) is characterized by the synthesis and secretion of calcitonin (Ct). MTC without Ct secretion has been reported on rare occasions. The aim of this study was to analyze the prevalence and clinical spectrum of nonsecretory MTC in two tertiary centers that cared for 839 patients with sporadic MTC. METHODS: Clinical, biochemical, histological, and immunohistological findings, and somatic RET mutations were analyzed, and long-term follow-up was documented. RESULTS: Seven patients with nonsecretory MTC were identified among 839 patients with sporadic MTC; thus, the prevalence rate of nonsecretory MTC was 0.83%. In these seven patients, Ct and carcinoembryonic antigen (CEA) levels were normal when MTC was initially diagnosed in the patients, despite advanced tumor stage. Ct and CEA levels remained undetectable in four patients; recurrence was indicated in one patient after 10 years of follow-up by routine anatomic imaging and increased CEA levels, and Ct levels became slightly elevated during follow-up, despite massive tumor load, in the remaining two patients. The diagnosis of MTC was confirmed by positive immunohistochemistry for Ct, CEA, and chromogranin A. A high Ki67 proliferation index (PI) (three patients) and a high proportion of RET 918-mutated cells (four patients), as well as poorly differentiated histology, were associated with aggressive biological behavior of the MTC. The prognosis for nonsecretory MTC varied between long-term survival (12.5 years) and rapid progression leading to death within 1.75 years after diagnosis. CONCLUSIONS: The prevalence of nonsecretory MTC was low (0.83% of patients with MTC). Diagnosis was often made at a clinically advanced tumor stage. The histological and immunohistological characteristics and the clinical course and prognosis of nonsecretory MTC are markedly heterogeneous. A high Ki-67 PI and a large proportion of cells with RET 918 mutations are associated with a poor prognosis.

Molecular genetics and phenomics of RET mutations: Impact on prognosis of MTC.

Multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominant hereditary cancer syndrome caused by missense gain-of-function mutations of the RET proto-oncogene. Three distinct clinical subtypes of MEN 2 have been characterized: MEN 2A, MEN 2B, and familial medullary thyroid carcinoma (FMTC). The specific RET mutation may suggest a predilection toward a particular phenotype and clinical course, with strong genotype-phenotype correlations. Recommendations on the timing of prophylactic thyroidectomy and extent of surgery are based on classification of RET mutations into risk levels according to genotype-phenotype correlations. The excellent prognosis for MTC diagnosed at its earliest stage underscores the importance of prospective screening (calcitonin screening) for sporadic MTC and early diagnosis by RET-mutation analysis for hereditary MTC. MEN 2 provides a unique model for early prevention and cure of cancer and for the roles of stratified mutation-based diagnosis and therapy of carriers.

Characterization of the RET protooncogene transmembrane domain mutation S649L associated with nonaggressive medullary thyroid carcinoma.

CONTEXT: For rare and novel RET mutations associated with hereditary medullary thyroid carcinoma (MTC), clinical and functional studies are needed to classify the RET mutation into one of the three clinical risk groups. OBJECTIVE: We analyzed proliferative properties and clinical implications associated with the RET protooncogene transmembrane domain mutation S649L. DESIGN: The transforming potential and mitogenic properties of S649L mutation were investigated clinically and by evaluating kinase activity, cell proliferation, and colony formation. PATIENTS: Fifteen individuals from five kindreds were identified as carriers of a RET protooncogene mutation in exon 11 codon 649 (TCG(Ser)-->TTG(Leu)). In two out of five index patients, a second RET mutation (C634W or V804L) was detected. RESULTS: Eight gene carriers were operated on. Histology revealed MTC and C-cell hyperplasia in three index and three screening patients respectively. In all other gene carriers (aged 41-64 years), calcitonin levels were in the normal range, and pentagastrin-stimulated calcitonin levels were <100 pg/ml. Therefore, thyroidectomy had not yet been performed. In one index patient carrying the S649L mutation, hyperparathyroidism was confirmed histologically. RET S649L-expressing NIH3T3 cells exhibited a clear increase of phosphotyrosine and proliferation rate when compared with parental NIH3T3 cells but a significantly lower kinase activity and cell growth rate when compared with RET C634R-expressing cells. When compared with RET C634R, the S649L mutant showed moderate transforming potential with small-sized colonies. CONCLUSIONS: Our clinical and in vitro findings indicate that the transmembrane RET S649L mutation is associated with late-onset non-aggressive disease. Recommendations for prophylactic thyroidectomy should be individualized depending on stimulated calcitonin levels.