Parent-of-origin effects in multiple endocrine neoplasia type 2B

Multiple endocrine neoplasia type 2B (MEN 2B) is characterized by medullary thyroid carcinoma, pheochromocytomas, mucosal neuromas, ganglioneuromas, and skeletal and ophthalmic abnormalities. It is observed as both inherited and sporadic disease, with an estimated 50% of cases arising de novo. A single point mutation in the catalytic core region of the receptor tyrosine kinase, RET, has been observed in germ-line DNA of MEN 2B patients. We have analyzed 25 cases of de novo disease in order to determine the parental origin of the mutated RET allele. In all cases the new mutation was of paternal origin. We observe a distortion of the sex ratio in both de novo MEN 2B patients and the affected offspring of MEN 2B transmitting males. These results suggests a differential susceptibility of RET to mutation in paternally and maternally derived DNA and a possible role for imprinting of RET during development.

Predictive DNA testing and prophylactic thyroidectomy in patients at risk for multiple endocrine neoplasia type 2A

BACKGROUND

Missense germ-line mutations in the RET protooncogene are associated with multiple endocrine neoplasia type 2A (MEN 2A). Detection of these mutant alleles in kindred members predicts disease inheritance and provides the basis for preventative thyroidectomy.

METHODS

A polymerase chain reaction (PCR)-based genetic test for the 19 known RET mutations was designed to study 132 members of 7 kindreds with MEN 2A. Haplotypes also were constructed using genetic markers flanking the MEN 2A locus. Plasma calcitonin (CT) concentrations were determined before and after provocative testing.

RESULTS

Direct DNA testing and haplotype analysis showed that 21 of 58 kindred members at risk for disease had inherited a mutation in the RET protooncogene associated with MEN 2A. Plasma CT concentrations were elevated in 9 of the 21 family members, but were normal in 12. After genetic counseling, 13 of the 21 kindred members (6 with normal and seven with elevated plasma CT levels), consented to immediate thyroidectomy. In each patient, the resected thyroid gland showed C-cell hyperplasia with or without medullary thyroid carcinoma. There were no metastases to regional lymph nodes, and postoperative stimulated plasma CT levels were normal.

CONCLUSION

The PCR-based direct DNA test for RET mutations is accurate, rapid, and reproducible. For all 132 individuals evaluated, the results of direct DNA analysis were consistent with haplotype studies. The direct test for mutations in the RET protooncogene is the preferred method for screening MEN 2A kindreds. In family members who have inherited a RET mutation, total thyroidectomy is indicated, regardless of the plasma CT values.

Predictive testing for multiple endocrine neoplasia type 2A (MEN 2A) based on the detection of mutations in the RET protooncogene

BACKGROUND

The identification of inherited mutations in the RET protooncogene (RET) associated with multiple endocrine neoplasia type 2A (MEN 2A) has enabled the development of a genetic test to identify asymptomatic carriers of disease.

METHODS

Genomic DNA was extracted from 96 members of an MEN 2A kindred. The polymerase chain reaction was used to amplify the RET exon known to contain the associated mutation. The mutation results in a new restriction endonuclease site and is detected by digestion with the appropriate enzyme. Inheritance of the mutation was verified with a previously developed genetic linkage test.

RESULTS

We found that (1) mutations vary among kindreds but are consistently inherited within kindreds, (2) invariable correlation exists between mutation and disease (43 mutations in 43 affected individuals), (3) determination of the genetic status by linkage-based testing was precluded by recombination events and the informativeness of genetic markers, and (4) mutation analysis presymptomatically identified two genetically affected individuals.

CONCLUSIONS

Direct genetic analysis for mutations in RET circumvents the limitations of linkage-based genetic testing and current biochemical screening assays. This method will be the diagnostic test of choice for the identification of asymptomatic individuals at risk for MEN 2A.

Surgical treatment of primary hyperaldosteronism

OBJECTIVE

A retrospective review of patients with primary hyperaldosteronism treated at the Duke University Medical Center was performed.

SUMMARY BACKGROUND DATA

The management of patients with primary hyperaldosteronism has changed dramatically in the past 20 years. The outcome of surgical treatment was examined to optimize the management of these patients.

METHODS

All patients who were evaluated for primary hyperaldosteronism before operation and who had adrenal surgery at Duke University Medical Center from 1970 to 1993 were included in the study.

RESULTS

A ratio of plasma aldosterone concentration to plasma renin activity greater than 250 was predictive of hyperaldosteronism in 94% of patients. This ratio also predicted the size of the adenoma. Surgical treatment cured hypokalemia in 90% of the patients. Hypertension was cured or greatly improved, with an average decrease of 50.4 mmHg and 25.2 mmHg for systolic and diastolic pressures, respectively. Patients who had hypertension for less than 5 years achieved a satisfactory blood pressure response more often (13 of 14 patients) than did patients who had hypertension for 5 or more years (15 of 20 patients).

CONCLUSIONS

Preoperative evaluation of patients with primary hyperaldosteronism using current modes allows a posterior approach to be used in most patients. Adrenalectomy cures hypokalemia and hypertension; however, patients with a history of hypertension for less than 5 years may be more likely to be cured by adrenal resection.

Stimulation of vasoactive intestinal peptide and neurotensin secretion by pentagastrin in a patient with VIPoma syndrome

BACKGROUND

Pancreatic endocrine tumors (PETs) may secrete a variety of peptide hormones, either alone or in combination, and intravenously administered provocative agents have been used to stimulate hormone release to aid in the diagnosis and localization in suspected cases. These features of PETs led us to perform detailed biochemical investigations and provocative testing in a 26-year-old man with a 5 cm vasoactive intestinal peptide (VIP)-secreting tumor of the head of the pancreas.

METHODS

Plasma hormone radioimmunoassays and immunohistochemical studies were performed for a panel of peptide hormones, including VIP, neurotensin, and pancreatic polypeptide (PP). Acid alcohol extracts of tumor specimens were analyzed for these peptide hormones as well. Before operation, four provocative test regimens were administered intravenously after an overnight fast: pentagastrin (0.5 microgram/kg/5 sec); rapid calcium infusion (2 mg/kg/min); a combination of calcium (2 mg/kg/min) followed by pentagastrin (0.5 microgram/kg/min); and secretin (2 clinical units/kg bolus). Blood samples were collected before each test and 1, 2, 3, 5, and 10 minutes after the infusions.

RESULTS

Measurement of plasma hormone levels and tumor immunohistochemistry and hormonal extraction studies indicated secretion of VIP, neurotensin, and PP by the tumor. Coexpression of VIP and neurotensin was seen immunohistochemically within some individual tumor cells. Provocative testing resulted in maximal stimulation of VIP and neurotensin secretion with pentagastrin administration, which produced increases in plasma levels of VIP and neurotensin over basal levels of 81% and 87%, respectively. After operation, plasma levels of VIP, neurotensin, and PP were undetectable before and after administration of pentagastrin.

CONCLUSIONS

The results emphasize the importance of comprehensive biochemical evaluation in patients with VIPoma syndrome to detect the production of a range of peptide hormones. Administration of intravenous pentagastrin appears to stimulate release of VIP and NT and should be evaluated further as a provocative agent for the diagnosis and follow-up of patients with these tumors.

Current perspectives on the diagnosis and management of patients with multiple endocrine neoplasia type 2 syndromes

Patients with MEN 2A, MEN 2B, and familial non-MEN medullary thyroid carcinoma (MTC) inherit MTC in an autosomal dominant fashion. This malignancy has been diagnosed previously by detecting elevated plasma calcitonin levels, a tumor marker for MTC, following the intravenous administration of secretagogues. Although the study of large pedigrees with MEN 2A, using highly informative flanking markers and linkage analysis, are highly accurate in predicting the inheritance of the disease, the method is indirect and somewhat cumbersome. Mutations in the RET proto-oncogene have been identified independently in patients with MEN 2A and familial medullary thyroid carcinoma. Even though the RET mutations are inherited with disease, there is no direct evidence that the mutations cause the MEN 2 syndromes. The usefulness of molecular methods in the diagnosis and treatment of patients with these syndromes is discussed, and a strategy for deciding operative intervention is presented.

Single missense mutation in the tyrosine kinase catalytic domain of the RET protooncogene is associated with multiple endocrine neoplasia type 2B

Multiple endocrine neoplasia type 2B (MEN 2B) is a human cancer syndrome characterized by medullary thyroid carcinoma (MTC), pheochromocytomas, mucosal neuromas, ganglioneuromas of the intestinal tract, and skeletal and ophthalmic abnormalities. It appears both as an inherited disorder and as de novo disease. Sequence analysis of germ-line DNA from MEN 2B patients revealed the existence of the same point mutation in the RET protooncogene in 34 unrelated individuals. This sequence difference was not observed in 93 unaffected individuals, including the normal parents of 14 de novo MEN 2B patients. The mutation (ATG-->ACG) results in the replacement of methionine with threonine within the catalytic core region of the tyrosine kinase domain. We propose that this amino acid replacement effects substrate interactions and results in dominant oncogenic activity by the RET protein. Missense mutations in the extracellular ligand-binding domain of the RET protooncogene previously have been associated with two other disorders [MEN 2A and familial MTC (FMTC)] in which MTC is observed. MEN 2B represents the third form of heritable MTC known to be an allele of RET. Alterations in two different functional domains of the putative receptor protein tyrosine kinase are implicated in development of MTC.

Prevalence of pheochromocytoma and hyperparathyroidism in multiple endocrine neoplasia type 2A: results of long-term follow-up

BACKGROUND

Multiple endocrine neoplasia type 2A (MEN 2A) is an autosomal dominant condition in which virtually all affected kindred members have medullary thyroid carcinoma (MTC). However, the penetrance of pheochromocytoma and hyperparathyroidism in affected kindred members is variable, and the true prevalence of these neoplasms is unclear from previous studies.

METHODS

Members of MEN 2A kindreds with more than 10 years of follow-up screening for MTC, pheochromocytoma, or hyperparathyroidism were studied. The diagnosis of pheochromocytoma was based on histologic examination and hyperparathyroidism on both parathyroid hyperplasia plus preoperative elevation of serum calcium levels.

RESULTS

Eighty-six patients operated on for MTC from 12 different MEN 2A kindreds were studied, with a mean follow-up of 12.9 years of screening for pheochromocytoma (79 patients) and 15.0 years for hyperparathyroidism (78 patients). Pheochromocytomas developed in 42% of patients with MTC, with a range of 6% to 100% in different kindreds. The prevalence of hyperparathyroidism was 35%, ranging from 0% to 53% between kindreds. The average age at diagnosis of MTC, pheochromocytoma, and hyperparathyroidism was 29, 37, and 36 years, respectively.

CONCLUSIONS

We conclude that the penetrance of pheochromocytoma and hyperparathyroidism is variable in different kindreds with MEN 2A but that the overall prevalence of pheochromocytoma approximates 40% and that of hyperparathyroidism 35%.

Reoperation for recurrent or persistent medullary thyroid cancer

BACKGROUND

Initial operations for medullary thyroid cancer (MTC) frequently do not eradicate all disease, as evidenced by persistently elevated levels of stimulated plasma calcitonin.

METHODS

Thirty-two patients with MTC and elevated stimulated plasma calcitonin levels after thyroidectomy were studied between 1990 and 1993. Thirty-five repeat neck explorations and microdissections were performed. Four patients also underwent a median sternotomy and mediastinal dissection.

RESULTS

In nine patients (group 1), stimulated plasma calcitonin levels were undetectable after reoperation, whereas in 13 cases (group 2) the calcitonin levels decreased by 40% or more. In 10 cases (group 3) the CT levels did not decrease. Primary tumors that exhibited invasive features (invasion of adjacent structures or extranodal or extracapsular spread) were found more often in patients from group 3 than in patients from groups 1 or 2 (p < 0.05, Fisher's exact test).

CONCLUSIONS

Reoperation resulted in normalization of calcitonin levels in 28% of patients and a decrease in calcitonin levels by 40% or more in another 42% of patients. The data also suggest that patients whose primary MTC has invaded tissues beyond the thyroid gland or a lymph node capsule are less likely to benefit from repeat operation.

Mutations in the RET proto-oncogene are associated with MEN 2A and FMTC

Multiple endocrine neoplasia type 2A (MEN 2A) and familial medullary thyroid carcinoma (FMTC) are dominantly inherited conditions which predispose to the development of endocrine neoplasia. Evidence is presented that sequence changes within the coding region of the RET proto-oncogene, a putative transmembrane tyrosine kinase, may be responsible for the development of neoplasia in these inherited disorders. Single strand conformational variants (SSCVs) in exons 7 and 8 of the RET proto-oncogene were identified in eight MEN 2A and four FMTC families. The variants were observed only in the DNA of individuals who were either affected or who had inherited the MEN2A or FMTC allele as determined by haplotyping experiments. The seven variants identified were sequenced directly. All involved point mutations within codons specifying cysteine residues, resulting in nonconservative amino acid changes. Six of the seven mutations are located in exon 7. A single mutation was found in exon 8. Variants were not detected in four MEN 2B families studied for all exon assays available, nor were they detectable in 16 cases of well documented sporadic medullary thyroid carcinoma or pheochromocytoma that were tested for exon 7 variants. Coinheritance of the mutations with disease and the physical and genetic proximity of the RET proto-oncogene provide evidence that RET is responsible for at least two of the three inherited forms of MEN 2. Neither the normal function, nor the ligand of RET are yet known. However, its apparent involvement in the development of these inherited forms of neoplasia as well as in papillary thyroid carcinoma suggest an important developmental or cell regulatory role for the protein.

Allelic loss on a chromosome 17 in ductal carcinoma in situ of the breast

Multiple tumor suppressor genes are implicated in the oncogenesis and progression of invasive carcinoma of the breast. To investigate the chronology of genetic changes we studied loss of heterozygosity on chromosome 17 in ductal carcinoma in situ, a preinvasive breast cancer. A microdissection technique was used to separate tumor from normal stromal cells prior to DNA extraction and loss of heterozygosity was assayed mainly using simple sequence repeat polymorphism markers and the polymerase chain reaction. Loss of heterozygosity on 17p was observed in 8 of 28 tumors (29%) when compared with normal control DNA, whereas no loss was seen on 17q, suggesting that at least one locus on 17p is involved early in the development of breast cancer.

Management of pheochromocytomas in patients with multiple endocrine neoplasia type 2 syndromes

OBJECTIVE

The authors sought to determine the optimal surgical management of pheochromocytomas that develop in patients with multiple endocrine neoplasia (MEN) type 2 syndromes.

SUMMARY BACKGROUND DATA

The performance of empirical bilateral adrenalectomy in patients with MEN 2A or MEN 2B, whether or not they have bilateral pheochromocytomas, is controversial.

METHODS

The results of unilateral or bilateral adrenalectomy were studied in 58 patients (49 with MEN 2A and 9 with MEN 2B). Recurrence of disease was evaluated by measuring 24-hour urinary excretion rates of catecholamines and metabolites and by computed tomography (CT) scanning.

RESULTS

The mean postoperative follow-up was 9.40 years. There was no operative mortality and malignant or extra-adrenal pheochromocytomas were not present. Twenty-three patients with a unilateral pheochromocytoma and a macroscopically normal contralateral gland underwent unilateral adrenalectomy. A pheochromocytoma developed in the remaining gland a mean of 11.87 years after the primary adrenalectomy in 12 (52%) patients. Conversely, 11 (48%) patients did not develop pheochromocytoma during a mean interval of 5.18 years. In the interval after unilateral adrenalectomy, no patient experienced hypertensive crises or other complications related to an undiagnosed pheochromocytoma. Ten (23%) of 43 patients having both adrenal glands removed (either at a single operation or sequentially) experienced at least one episode of acute adrenal insufficiency or Addisonian crisis, including one patient who died during a bout of influenza.

CONCLUSIONS

Based on these data, the treatment of choice for patients with MEN 2A or MEN 2B and a unilateral pheochromocytoma is resection of only the involved gland. Substantial morbidity and significant mortality are associated with the Addisonian state after bilateral adrenalectomy.

Development of a sequence-tagged site for the centromere of chromosome 10: its use in cytogenetic and physical mapping

We sequenced the alphoid centromere probe p alpha 10RP8 (D10Z1), aligned it to three published consensus sequences, and developed a sequence-tagged site (STS), sJRH-2, based upon oligonucleotide primers having two 3' mismatches with these consensus sequences. Polymerase chain reaction (PCR) amplification using genomic DNA from a somatic cell hybrid panel representing all human chromosomes demonstrated amplification from only those cell lines containing chromosome 10. Fluorescence in situ hybridization of the amplified product demonstrated intense and specific hybridization of the PCR product to 10p11.1-q11.1. A human genomic yeast artificial chromosome (YAC) library was screened using the sJRH-2 PCR assay, and five clones were identified. Sequence analysis of one chimeric clone (consisting of DNA segments derived from chromosomes 5p and 10cen) confirmed specificity of the STS for the centromere of chromosome 10. sJRH-2 provides a convenient cytogenetic marker for chromosome 10, which will also be useful for physical mapping of the pericentromeric region of chromosome 10, a region that harbors the gene(s) for three forms of multiple endocrine neoplasia (types 2A, 2B, and familial medullary thyroid carcinoma). The GenBank accession number for the p alpha 10RP8 sequence is X63622.

Parathyroid autotransplantation

It has been clearly shown clinically that parathyroid tissue can be successfully autotransplanted and even allotransplanted if the host is immunosuppressed. Engraftment is almost always successful; however, if abnormal tissue has been transplanted, its function will continue to be abnormal if the same intrinsic (e.g., primary parathyroid hyperplasia) or extrinsic (renal osteodystrophy) stimulation existing before grafting continues in the postoperative period. In these patients the secretion of parathyroid hormone from the grafted parathyroid tissue can be shown to progressively increase with time. Although parathyroid autotransplantation is most frequently performed clinically for renal osteodystrophy, there is controversy about the operation, and some surgeons prefer the technique of 3 1/2 gland parathyroidectomy. Because of the generally good results with total parathyroidectomy and autotransplantation in patients with primary parathyroid hyperplasia, this procedure seems to be the operation of choice in this clinical setting. The clearest indication for parathyroid autotransplantation is in patients with radical operations on the thyroid gland or other head and neck organs where the parathyroids have been damaged or their viability is questioned.

A 1.5-megabase yeast artificial chromosome contig from human chromosome 10q11.2 connecting three genetic loci (RET, D10S94, and D10S102) closely linked to the MEN2A locus

The genetic loci RET, D10S94, and D10S102 from human chromosome 10q11.2 are very closely linked to a locus responsible for the multiple endocrine neoplasia type 2 (MEN2A and MEN2B) and medullary thyroid carcinoma (MTC1) familial cancer syndromes. We have constructed a 1.5-megabase contig consisting of six genomic yeast artificial chromosome clones which include these loci and define their physical order. A critical crossover event has been identified within the map interval; this event places the MEN2A locus centromeric to D10S102 and defines the orientation of the physical map on the chromosome. The orientation of the contig and order of the markers are centromere-RET-D10S94-D10S102-telomere. In addition, a microsatellite repeat polymorphism with a heterozygosity of 71% at the RET locus and a restriction fragment length polymorphism with a heterozygosity of 42% detected by a lambda clone from the D10S94 locus have been developed for high-resolution genetic linkage mapping and predictive diagnostic testing. These data place three important markers on a contiguous physical map, narrow the MEN2 disease locus interval, and provide a framework for further candidate gene identification efforts. Placement of these genetic loci along a clone-based map and continued expansion of the contig will also facilitate efforts to determine the relationship of physical to genetic distance near the centromeres of human chromosomes.

Improved predictive test for MEN2, using flanking dinucleotide repeats and RFLPs

Gene(s) for the autosomal dominant endocrine cancer syndromes, multiple endocrine neoplasia type 2A (MEN2A), multiple endocrine neoplasia type 2B (MEN2B), and familial medullary thyroid carcinoma (MTC1) all map to the pericentromeric region of chromosome 10. Predictive testing for the inheritance of mutant alleles in individuals at risk for these disorders has been limited by the availability of highly informative and closely linked flanking markers. We describe the development of eight new markers, including two PCR-based dinucleotide repeat polymorphisms and six RFLPs that flank the disease loci. One of the dinucleotide repeat markers (sJRH-1) derives from the RBP3 locus on 10q11.2 and has a PIC of .88. The other dinucleotide repeat (sTCL-1) defines a new locus, D10S176, that maps by in situ hybridization to 10p11.2 and has a PIC of .68. We have constructed a new genetic linkage map of the pericentromeric region of chromosome 10, on the basis of 13 polymorphisms at six loci, which places the MEN2A locus between the dinucleotide repeat markers, with odds of 5,750:1 over the next most likely position. Using this set of markers, predictive genetic testing of 130 at-risk individuals from six families segregating MEN2A revealed that 95% were jointly informative with flanking markers, representing a significant improvement in genetic testing capabilities.

Presymptomatic identification of carriers of the multiple endocrine neoplasia type 2A gene using flanking DNA markers

BACKGROUND

Because the predisposition locus for multiple endocrine neoplasia type 2A (MEN2A) has been mapped to chromosome 10 by genetic linkage analysis, it has become possible to identify gene carriers by following the transmission of linked genetic markers from affected parents to offspring at risk for MEN2A. We have applied a highly accurate genetic test to presymptomatic diagnosis of gene carriers in several large kindreds with MEN2A.

METHODS

DNA was extracted from 300 individuals in six kindreds with MEN2A and used for genotyping studies with DNA markers flanking the MEN2A locus. Genotype data were used to predict the inheritance of the MEN2A gene in kindred members at risk according to previously calculated map distances and the program LINKAGE:

RESULTS

Ninety-five percent of individuals were informative with markers flanking the MEN2A locus. Of 130 patients at risk, 26 (20%) were predicted to be MEN2A gene carriers, 100% (77%) were noncarriers, and 4 (3%) were recombinant and their gene carrier status could not be determined. Gene carrier prediction probabilities were calculated at greater than 98% in 94% of these patients.

CONCLUSIONS

We conclude that genetic testing with flanking DNA markers is a highly accurate method for the presymptomatic identification of MEN2A gene carriers and allows for diagnosis at an earlier stage than does traditional calcitonin testing.

A minisatellite and a microsatellite polymorphism within 1.5 kb at the human muscle glycogen phosphorylase (PYGM) locus can be amplified by PCR and have combined informativeness of PIC 0.95

We sequenced a genomic clone (pMCMP1), previously reported to detect a VNTR polymorphism at the PYGM locus, and found a dinucleotide repeat segment (CA)14(GA)25 and a complex (AT)-repeat-rich segment containing 63 repeats spanning 160 bp. Resolution of PCR-amplified genomic DNA from the (CA)(GA) repeat region on DNA sequencing gels revealed a highly informative polymorphism with alleles differing by 2-bp intervals and ranging in size from 156 to 190 bp. Among three racial groups, a total of 18 alleles were observed. Fourteen alleles were observed in Caucasians (PIC 0.89), 12 alleles in American Blacks (PIC 0.89), and 9 alleles in Pima Indians (PIC 0.73). PCR amplification of the (AT) repeat region and resolution of the products on DNA sequencing gels revealed a complex variable length polymorphism with alleles distributed in size from 367 to 970 bp. Twenty-eight alleles were found in American Blacks (PIC 0.94), 6 alleles in Pima Indians (PIC 0.70), and 11 alleles in Caucasians (PIC 0.71). Comparison of the previously described VNTR RFLP alleles visualized by Southern hybridization to the PCR products described in this report demonstrated that the polymorphism described in both assays was identical. However, a larger number of alleles could be detected from the PCR-amplified products. Combined informativeness, PIC 0.95, for the two polymorphisms was determined from haplotype analysis of 100 Caucasian chromosomes. Therefore, for genotyping purposes, informativeness is maximized from using both polymorphisms.

Consistent association of 1p loss of heterozygosity with pheochromocytomas from patients with multiple endocrine neoplasia type 2 syndromes

Pheochromocytomas and medullary thyroid cancers (MTCs) are neuroendocrine tumors which arise sporadically or as part of the multiple endocrine neoplasia type 2 (MEN-2) hereditary syndromes. The most consistent molecular genetic abnormality which has been described in these tumors is loss of heterozygosity (LOH) of the short arm of chromosome 1 (1p). This finding is particularly interesting because the predisposition gene for the hereditary form of these tumors has been mapped to chromosome 10, but LOH on chromosome 10 in MEN-2 tumors is found rarely. We have used a battery of 1p DNA probes to elucidate the region of loss of 1p in 18 pheochromocytomas and 27 MTCs. Using restriction fragment length polymorphism analysis, we identified loss of all or a portion of 1p in 12 of 18 pheochromocytomas. 1p LOH was identified in nine of nine pheochromocytomas in MEN-2A and -2B patients, compared with only two of seven sporadic pheochromocytomas. We also found 1p LOH in one of two von Hippel-Lindau patients. LOH on 1p was noted in only three of 24 informative MTCs, and these were from patients with MEN-2A. In most of the pheochromocytomas, the entire short arm of chromosome 1p appears to have been lost; however, in three of the non-MEN pheochromocytomas and in three MEN-2A MTCs, the region of loss is smaller, allowing estimation of the smallest region of overlap. The combined data for MTCs and pheochromocytomas suggest that the smallest region of overlap of LOH is bounded by D1S15 (1pter-p22) and D1Z2 (1P36.3), excluding a region around MYCL (1p32). Although other regions of 1p should not be completely ruled out, the data suggest that this region may harbor a tumor suppressor gene or genes whose inactivation is important in the development of these tumors. Furthermore, the strong association between 1p LOH and the MEN-2 syndromes, especially in pheochromocytomas, suggests a relationship between the predisposition gene on chromosome 10 and the loss of the suppressor gene on 1p. Alternatively, other loci may be more important in sporadic disease.

Fine-scale mapping of the gene responsible for multiple endocrine neoplasia type 1 (MEN 1)

We have constructed a high-resolution genetic linkage map in the vicinity of the gene responsible for multiple endocrine neoplasia type 1 (MEN1). The mutation causing this disease, inherited as an autosomal dominant, predisposes carriers to development of neoplastic tumors in the parathyroid, the endocrine pancreas, and the anterior lobe of the pituitary. The 12 markers on the genetic linkage map reported here span nearly 20 cM, and linkage analysis of MEN1 pedigrees has placed the MEN1 locus within the 8-cM region between D11S480 and D11S546. The markers on this map will be useful for prenatal or presymptomatic diagnosis of individuals in families that segregate a mutant allele of the MEN1 gene.