Occurrence of MEN 2a in familial Hirschsprung's disease: a new indication for genetic testing of the RET proto-oncogene.

PURPOSE: The association of the rare hereditary cancer syndrome, multiple endocrine neoplasia type 2a (MEN 2a) with Hirschsprung's disease, both linked to germline mutations in the RET proto-oncogene, has been reported recently. With the widespread availability of genetic screening for MEN 2a, it is necessary to define the indications for genetic testing of MEN 2a and population subgroups at high risk for inheriting the disease. The purpose of this study was to assess the prevalence of Hirschsprung's disease in MEN 2a and investigate the value of genetic analysis for MEN 2a in children with familial Hirschsprung's disease. METHODS: The ethnically diverse study group consisted of unselected consecutive patients (n=426) at risk for hereditary medullary thyroid cancer (MTC) referred to a single laboratory for genetic testing. Analysis used genomic DNA and a polymerase chain reaction-based heteroduplex mutation detection strategy for exons 10, 11, 13, and 14 of the RET proto-oncogene followed by direct DNA sequencing. Significance of RET genotype-phenotype correlation was determined by Fisher's two-tailed Exact test and a 2 x 2 contingency table. RESULTS: Thirty-six distinctly new MEN 2a kindreds were identified. Hirschsprung's disease cosegregated among siblings with MEN 2a in 15 patients from 6 of the 36 (17%) families. The extent of aganglionosis in the 15 patients ranged from midrectum to duodenum. Of the 15 patients with Hirschsprung's disease, 10 (six boys, four girls) underwent thyroidectomy for MTC (n=5) or C-cell hyperplasia (n = 5) at ages 2 to 47 years (mean, 15.6 years), and the remaining five patients died in childhood of complications related to the aganglionosis. In retrospect, Hirschsprung's disease was the presenting feature of MEN 2a in five of the six families rather than MTC or pheochromocytoma. In all six MEN 2a families expressing Hirschsprung's disease, the RET mutation predisposing to the combined phenotype occurred in exon 10 at codons 609 (n=2), 618 (n=3), or 620 (n = 1). By contrast, the MEN 2a with Hirschsprung's phenotype was not found in any of the 22 families with a RETexon 11, 13, or 14 mutation (P=.0007). CONCLUSIONS: The authors conclude that Hirschsprung's disease is a phenotypic marker for MEN 2a and possibly more common than originally appreciated. The expression of Hirschsprung's disease with MEN 2a may be uniquely linked to RETexon 10 mutations. The authors recommend that (1) patients affected with MEN 2a may be counseled regarding the potential risk of Hirschsprung's disease in offspring and (2) a family history of MTC be explored in children with familial Hirschsprung's disease and genetic screening for MEN 2a be considered.

Hirschsprung disease in MEN 2A: increased spectrum of RET exon 10 genotypes and strong genotype-phenotype correlation.

The RET proto-oncogene encodes a transmembrane receptor with tyrosine kinase activity. Germline mutations in RET are responsible for a number of inherited diseases. These include the dominantly inherited cancer syndromes multiple endocrine neoplasia types 2A and 2B (MEN 2A and MEN 2B) and familial medullary thyroid carcinoma (FMTC), as well as some cases of familial Hirschsprung disease (HSCR1). RET mutations in HSCR1 have been shown to cause a loss of RET function, while the cancer syndromes result in RET oncogenic activation. Occasionally MEN 2A or FMTC occurs in association with HSCR1, albeit with low penetrance. An initial report linked HSCR1 in MEN 2A solely to the C618R and C620R RET mutations. In this study we have analyzed 44 families with MEN 2A. HSCR1 co-segregated with MEN 2A in seven (16%) of the 44 families. The predisposing RET mutation in all seven families had been previously reported in MEN 2A or FMTC and occurred in exon 10 at codons 609, 618 or 620, resulting in C609Y, C618S, C620R or C620W substitution. MEN 2A families with RET exon 10 Cys mutations had a substantially greater risk of developing HSCR1 than those with the more common RET exon 11 Cys634 or exon 14 c804 mutations (P = 0.0005). These findings suggest that expression of HSCR1 in MEN 2A may be peculiar to RET exon 10 Cys mutations . However, HSCR1 in MEN 2A is not exclusive to C618R or C620R RET mutations and can occur with other exon 10 Cys amino acid substitutions. The strong correlation between disease phenotype and position of the MEN 2A RET mutation suggests that oncogenic activation of RET alone is insufficient to account for co-expression of the diseases.

Prophylactic surgery for multiple endocrine neoplasia type IIa after genetic diagnosis: is parathyroid transplantation indicated?

Identification of germline mutations in the RET proto-oncogene predisposing to multiple endocrine neoplasia type IIa (MEN-IIa) has allowed a DNA-based approach to diagnosis and treatment by prophylactic thyroidectomy in children testing genetically positive. Although total thyroidectomy is the accepted operation for C cell disease, the necessity of routine total parathyroidectomy and autotransplantation as previously described in these asymptomatic children is questionable, particularly given the low occurrence of hyperparathyroidism in MEN-IIa (10-20%). Thirty-six children (ages 1 month to 12 years) from four MEN-IIa kindreds at risk for disease underwent genetic testing. Mutational analysis was done using a highly sensitive PCR-based denaturing gradient gel electrophoresis technique. Parathyroid or serum calcium concentrations were determined preoperatively. Of the 36 children at risk, 18 were found to have a MEN-IIa mutation; 11 have undergone prophylactic thyroidectomy at ages ranging from 2 to 12 years (mean 7.5 years). In each case, there was no biochemical evidence of hypercalcemia preoperatively, and all parathyroid glands were identified and were found to be grossly normal at exploration. Glands were carefully dissected and left in situ. Postoperatively, 10 of the 11 children maintained normocalcemia, allowing discharge within 24 to 36 hours. Resected thyroid glands contained C cell hyperplasia in nine, medullary carcinoma in one, and normal histology in one. We conclude that an alternative to routine parathyroidectomy may be desirable for prophylactic treatment of MEN-IIa. In situ parathyroid preservation can be safely achieved without compromising the completeness of the thyroid resection. This conservative approach obviates the potential morbidity associated with total parathyroidectomy and autotransplantation.

Detection of RET mutations in multiple endocrine neoplasia type 2a and familial medullary thyroid carcinoma by denaturing gradient gel electrophoresis.

Germline missense mutations within the coding region of the RET proto-oncogene have recently been described in patients with the dominantly inherited cancer syndromes, multiple endocrine neoplasia type 2a (MEN 2a) and familial medullary thyroid carcinoma (FMTC). To date, the sequence variations occur in RET exons 10 and 11 and alter highly conserved cysteine residues in the proposed extracellular domain at codons 609, 611, 618, 620, and 634. To expedite rapid screening of populations at risk of MEN 2a or FMTC, we developed a PCR-based denaturing gradient gel electrophoresis (DGGE) strategy that detects polymorphisms occurring at all five Cys codons in both RET exons using identical gel conditions. In this report, the screening results from DGGE analysis of 15 distinct MEN 2a and FMTC mutations are shown. Each mutation generated a clearly distinguishable and unique homo- and heteroduplex band pattern. Given the highly efficient, reproducible, and sensitive nature of this approach, DGGE is particularly appropriate for rapid, large-scale screening of patients. Since prior knowledge of the RET mutation is unnecessary for analysis, DGGE is potentially valuable for distinguishing germline from seemingly sporadic medullary thyroid cancer as well as identifying novel sequence changes.

Progress in genetic screening of multiple endocrine neoplasia type 2A: is calcitonin testing obsolete?

BACKGROUND: Recent identification of RET mutations in multiple endocrine neoplasia type 2A (MEN 2A) allows a DNA-based approach to diagnosis in lieu of calcitonin sampling. To prospectively evaluate the efficacy of mutational analysis, genetic screening was performed in 124 patients (53 male, 71 female; age, 1 month to 80 years) at risk for MEN 2A referred over 3 months. METHODS: Analysis used genomic DNA and a polymerase chain reaction-based denaturing gradient gel electrophoresis strategy for mutation detection at RET codons 609, 611, 618, 620, and 634. Ninety-three of 124 patients were from established MEN 2A kindreds (group A), and screening replaced calcitonin testing. Twenty-one of 124 patients (group B) represented index cases of medullary thyroid carcinoma (MTC), and DNA analysis was performed to distinguish sporadic from hereditary disease. Ten patients (group C) had modest calcitonin elevations or had undergone thyroidectomy without confirming pathologic results, and testing was undertaken to clarify status. RESULTS: Group A: RET mutations occurred in 29 (median age, 10 years) of 93 patients, 14 of whom underwent thyroidectomy. No false-positive results were observed. Group B: five (24%) of 21 patients with seemingly sporadic MTC had RET mutations at codons 618 (one), 620 (one), or 634 (three). Group C: Nine of 10 patients with alleged MEN 2A had genetically negative results. CONCLUSIONS: Denaturing gradient gel electrophoresis reliably detects MEN 2A. Modest calcitonin elevations may lead to a false-positive diagnosis of MTC. DNA testing is the optimal approach to evaluating MEN 2A. Index cases of sporadic MTC should also undergo DNA analysis.

Mutational analysis of multiple endocrine neoplasia type 2A associated with Hirschsprung's disease.

BACKGROUND: The clinical association of multiple endocrine neoplasia type 2A (MEN 2A) and Hirschsprung's disease (HD), although rare, has been previously observed. Recently, germline mutations in the RET proto-oncogene, a transmembrane receptor with tyrosine kinase activity, have been detected in patients with familial HD. RET is also the predisposition gene for the inherited cancer syndrome MEN 2A. METHODS: We describe a DNA sequence variation within the coding region of RET in two large unrelated kindreds with MEN 2A (with 83 and 42 persons affected) in which HD cosegregated with MEN 2A in seven patients. Mutational analysis was performed with a highly sensitive polymerase chain reaction-based denaturing gradient gel electrophoresis technique followed by direct sequencing of mutants. RESULTS: Genetic analysis by denaturing gradient gel electrophoresis detected mutant bands in RET exon 10 in patients with MEN 2A from both kindreds. Direct DNA sequencing of mutants revealed a thymine-to-adenine base change in codon 618, resulting in a cysteine-to-serine substitution. The identical mutation was present in all seven children with HD. Of these children five underwent thyroidectomy for C-cell abnormalities; one 3-year-old child is awaiting thyroid surgery, and the remaining patient died at age of 12 weeks. CONCLUSIONS: The RET codon 618 Ser mutation could predispose patients with MEN 2A to HD. RET may assume a critical role in embryologic enteric nerve migration and tumorigenesis of cells from neural crest lineage.

Novel amyloid precursor protein gene mutation (codon 665Asp) in a patient with late-onset Alzheimer's disease.

Amyloid plaques in Alzheimer's disease contain beta-amyloid, encoded by portions of exons 16 and 17 of the amyloid precursor protein. The specific association of rare amyloid precursor protein mutations with some kindreds with early-onset familial Alzheimer's disease suggests that specific abnormalities in amyloid precursor protein may contribute to the pathogenesis of Alzheimer's disease. Until now, there has been no evidence suggesting that amyloid precursor protein mutations could be involved in late-onset or sporadic Alzheimer's disease. We used reverse transcription-polymerase chain reaction, denaturing gradient gel electrophoresis, and direct DNA sequencing to analyze amyloid precursor protein exons 16 and 17 from postmortem cerebellar samples from patients with histologically confirmed Alzheimer's disease and control subjects. We found a novel point mutation, substitution of cytosine for guanine, at nucleotide 2119 (amyloid precursor protein 770 messenger RNA transcript) in a patient with late-onset Alzheimer's disease. This substitution deletes a BglII site and substitutes aspartate for glutamine at codon 665. Denaturing gradient gel electrophoresis analysis showed that this mutation was absent in 40 control subjects and 127 dementia patients. Whether this mutation is a rare but normal variant or contributes to the development of Alzheimer's disease is not known. The BglII restriction fragment length polymorphism enables investigators to determine the frequency of this polymorphism in normal subjects and Alzheimer's disease patients.

ApoE epsilon 4 allelic association with Alzheimer's disease: independent confirmation using denaturing gradient gel electrophoresis.

There is intriguing evidence associating apolipoprotein E (ApoE) with Alzheimer's disease (AD). ApoE is deposited with beta-amyloid in senile plaques and binds to beta-amyloid in vitro. We used denaturing gradient gel electrophoresis to identify ApoE epsilon 2, epsilon 3, and epsilon 4 alleles in 135 control subjects and 57 AD patients. We observed a marked increase in ApoE epsilon 4 allele frequency (0.40) in AD patients compared with control subjects (0.14) (p < 0.0001). Our independent finding of a marked association of ApoE epsilon 4 allele with AD further supports a possible role of ApoE in the pathogenesis of AD and confirms the study of Saunders et al (Neurology 1993;43:1467-1472).

Detecting prion protein gene mutations by denaturing gradient gel electrophoresis.

Mutations of the prion protein (PrP) gene are present in patients with Gerstmann-Sträussler-Scheinker syndrome (GSS), familial Creutzfeldt-Jakob disease (CJD), and fatal familial insomnia (FFI). We developed a denaturing gradient gel electrophoresis (DGGE) strategy that readily identifies point mutations in the PrP coding sequence. By comparison with appropriate controls, haplotypes often may be deduced. This method permits samples from many patients with GSS, CJD, as well as patients with unusual degenerative neurologic disorders, to be screened rapidly, sensitively, and inexpensively for the presence of known and novel PrP mutations. We illustrate the sensitivity of this approach by reporting 2 novel polymorphisms in the PrP coding sequence.

Novel polymorphism in the A4 region of the amyloid precursor protein gene in a patient without Alzheimer's disease.

We found a novel polymorphism in the amyloid precursor protein (APP) gene in a patient with ischemic cerebrovascular disease who had no evidence of Alzheimer's disease (AD). This polymorphism deletes a Fok I restriction enzyme site and causes the substitution of threonine for alanine at codon 673. This is adjacent to the site at which APP is thought to undergo cleavage in AD. Analysis of this polymorphism may provide insight into the basis of APP processing.

Allele-specific sequencing confirms novel prion gene polymorphism in Creutzfeldt-Jakob disease.

We analyzed the prion protein coding sequence in a familial Creutzfeldt-Jakob disease patient who did not have any of the currently recognized prion protein mutations. Denaturing gradient gel electrophoresis indicated that the prion protein coding sequence was heterozygous at least one location. We isolated each allele by denaturing gradient gel electrophoresis and directly sequenced. We found a DNA polymorphism at codon 178 that predicted the amino acid substitution, aspartate----asparagine. Whether this represents a benign polymorphism or pathogenic mutation will depend on analysis of the functional consequences of this change. Denaturing gradient gel electrophoresis and allele-specific sequencing proved to be efficient means of analyzing sequence polymorphisms in this gene.

Insulin binding to microvascular endothelium of intact heart: a kinetic and morphometric analysis.

We have studied insulin binding to blood vessels of the intact, beating heart. The beating hearts were perfused with [125I]iodoinsulin (3 X 10(-10) M) followed by perfusion with unlabeled insulin. The unlabeled insulin displaced the bound [125I]iodoinsulin in direct proportion to the concentration of the unlabeled hormone. Perfusion with unlabeled insulin at 10(-11) M elicited a significant displacement of [125I]iodoinsulin, with a maximal effect at 10(-6) M. Unlabeled proinsulin also displaced [125I]iodoinsulin in a dose-dependent manner, being 1% as potent as insulin. Perfusion with unrelated peptides had no effect. Radioautographic counting of 125I grains indicated that greater than 95% of the grain counts over blood vessels were within the microvessels. When [125I]iodoinsulin perfusion was followed by perfusion with unlabeled insulin at 10(-6) M, there was a 50% decrease in grain counts over the microvessels (versus perfusion with [125I]iodoinsulin alone); with coperfusion of [125I]iodoinsulin and 10(-6) M unlabeled insulin, an 80% decrease in grain counts occurred. Electron microscopic radioautography indicated that the 125I grains were associated with the vascular endothelial cells. We conclude that specific insulin receptors are present on endothelial cells of microvessels in the intact heart.

Interactions of multiplication-stimulating activity with bovine endothelium: comparative studies in primary, passaged, and cloned cultures from the pulmonary and systemic circulations.

Endothelial cells were prepared from adult bovine pulmonary and systemic vessels and maintained as primary cultures, passaged cultures, and cloned cell strains. All cultures were shown to contain endothelial cells on the basis of several endothelial-specific and endothelial-associated traits. Both primary and passaged cells demonstrated specific receptors for the insulin-like growth factor, multiplication-stimulating activity (MSA). [125I]Iodo-MSA binding was greatest in cells derived from aortas, least in pulmonary venous cells, and intermediate in pulmonary arterial cells. When compared to MSA receptors on primary endothelial cell cultures derived from human umbilical veins or arteries, the bovine cells bound 4-10 times more MSA per cell. In all bovine cells, insulin competed weakly or not at all with [125I]iodo-MSA binding. The presence of MSA receptors on primary and passaged cells from five different vascular sources (three bovine and two human) suggests that receptors for the insulin-like growth factors may be an intrinsic component of the vascular endothelium.

Comparison of insulin binding to cells of fed and fasted obese patients: results in erythrocytes and monocytes.

The erythrocyte (RBC) has received recent interest as a cell model to examine insulin receptor status in humans. In the present study we have compared the insulin receptors on mature RBCs and monocytes of four hyperinsulinemic obese patients in the fed state and after a 14-day fast (less than 50 cal/day). Insulin binding in the basal (fed) state was described in RBC and monocytes due predominantly to a decrease in the receptor concentration in both cell types. After a 14-day fast, insulin binding to both RBCs and monocytes increased significantly in each patient. Maximal binding of [125I]iodoinsulin to RBCs increased by 29% (range, 20-46%), and binding to monocytes increased by 116% (range, 46-321%). In response to the fast, the concentration of insulin needed to inhibit binding by 50% decreased from 5 to 2 ng/ml in RBC and from 3 to 1 ng/ml in monocytes. Conventional and computer-fitted Scatchard analyses demonstrated no change in the receptor concentration of RBCs of any patient, whereas the receptor concentration of monocytes increased by more than 50% in two of the four patients and by 40% for the group. Thus, in response to the fast, the direction of the change in insulin binding was similar in the RBCs and monocytes, whereas the magnitude and, in certain patients, the mechanism of the binding increase differed.

Interactions of insulin with bovine endothelium.

Bovine endothelial cells have been isolated from pulmonary and systemic vessels and grown in culture as primary, passaged and passaged cloned-strains. The cultures were shown to be endothelial in nature on the basis of several endothelial-specific and endothelial-associated traits. Endothelial cells from all sources had specific receptors for insulin in primary culture and after serial passage. Endothelial cells derived from pulmonary arteries and aortas bound 2.5 times more insulin than cells derived from the pulmonary vein. Each endothelial cell type maintained a specific complement of receptors through at least 25 passages in vitro. Coupled with previous findings of insulin receptors on endothelial cells from human umbilical vessels, these data suggest that insulin receptors may be an intrinsic component of all vascular endothelium.

Receptors for multiplication-stimulating activity on human arterial and venous endothelial cells.

Primary cultures of endothelial cells were prepared from the arteries and veins of human umbilical cords. Both arterial and venous endothelial cells demonstrated specific receptors for the insulin-like growth factor MSA (Multiplication-Stimulating Activity). Insulin, at concentrations up to 10(-7) M, had little effect on 125I-MSA binding whereas MSA was congruent to 1% as potent as insulin in competing with 125I-insulin binding. Serum containing anti-insulin receptor antibodies blocked binding of 125I-insulin to the endothelial cells but had little effect on 125I-MSA binding. We conclude that human endothelial cells have specific and distinct receptors for both MSA and insulin.

Differential binding of insulin to human arterial and venous endothelial cells in primary culture.

The properties of 125I-insulin binding were assessed in endothelial cells prepared from the veins and the arteries of human umbilical cords. The endothelial nature of both the natural and venous cultures were documented by the presence of characteristic endothelial features, including Weibel-Palade bodies, factor VIII antigen, and morphology. Both arterial and venous cells possessed typical receptors for insulin on the basis of specificity of binding, curvilinear Scatchard plots, affinity profiles, pH dependency, and dissociation kinetics. Arterial cells bound at least 2.5 times more insulin than did venous cells, whether studied at 4 h, 24 h, or 72 h after in vitro plating. We conclude that (1) specific receptors for insulin are present on human arterial as well as human venous endothelial cells and (2) the concentration of insulin receptors varies among endothelial cells derived from different vascular sources.

Insulin receptors in human endothelial cells: identification and characterization.

Specific binding of 125I-insulin was found in cultured human endothelial cells obtained from human umbilical veins. The binding reaction was rapid and reversible, demonstrated receptor site-site interactions of the negatively cooperative type, and was dependent on the temperature, pH and duration of incubation. At 21 degrees C, steady-state conditions of binding occurred in 90 minutes, the pH optimum was 7.8 and less than 10% of the labeled hormone was degraded. Binding of tracer amounts of 125I-insulin was inhibited by concentrations of unlabeled insulin as low as 0.2 ng/ml and 50% inhibition was obtained at 2-5 ng/ml of unlabeled insulin. Unlabeled porcine insulin, porcine proinsulin and desoctapeptide insulin inhibited the binding of 125I-porcine insulin in direct proportion to their biological potencies, whereas to the cells was inhibited by antibodies against insulin receptors. We conclude that human endothelial cells possess specific receptors for insulin whose physio-chemical properties are similar to those of insulin receptors in other tissues.