Multiple endocrine neoplasia type 2A c804 RET mutation as an indication for prophylactic thyroidectomy

Background

Missense mutations in five exons of the RET proto-oncogene have been found to cosegregate with the inherited cancer syndrome, multiple endocrine neoplasia type 2A (MEN2A). Sequence abnormalities involving c804 in exon 14 occur rarely and to date have been found in five kindreds. Initial reports linked the c804 mutation to a mild C-cell disease phenotype with low penetrance and an indolent course, and questioned the appropriateness of aggressive strategies such as prophylactic thyroidectomy in early childhood. The purpose of this study is to report the clinical correlates of five additional MEN2A kindreds that harbour the c804 RET mutation, with the intention of clarifying therapeutic recommendations in asymptomatic carriers.

Methods

Thirty-eight members from five distinct kindreds at risk for the c804 mutation underwent genetic analysis using genomic DNA and direct DNA sequencing. Operative and pathology reports were reviewed. Detection of C-cell hyperplasia (CCH) or medullary thyroid carcinoma (MTC) was accomplished biochemically by baseline or pentagastrin-stimulated calcitonin determinations.

Results

Twenty-three gene carriers were identified. The predisposing c804 missense mutation in each case resulted in a TTG, ATG or CTG substitution. Of the 23 patients testing genetically positive, 14 proceeded to thyroidectomy. At operation, MTC was found in seven patients (age 6–56 years), CCH in six patients (age 13–40 years) and normal thyroid histology was present in a single patient (age 27 years). One of the seven patients with MTC died from widespread metastases at age 12 years. Nine of the 23 gene carriers delayed operative intervention. Four of the nine patients have undergone biochemical testing. Three of the four patients have a raised calcitonin level and a single patient remains clinically and biochemically negative at age 40 years.

Conclusion

Penetrance of the c804 mutation is highly variable. In contrast to initial reports, however, MTC associated with sequence abnormalities at this site has aggressive potential. Therefore, prophylactic thyroidectomy remains a reasonable approach in children testing genetically positive.

Update on the MEN 2A c804 RET mutation: is prophylactic thyroidectomy indicated?

BACKGROUND

Mutations of the RET proto-oncogene co-segregate with multiple endocrine neoplasia type 2A. A rare sequence abnormality at codon 804 (c804) has been reported in 6 kindreds and linked to mild C-cell disease, which raises the question of the appropriateness of thyroidectomy in childhood. The purpose of this study was to (1) report the clinical correlates of 5 additional c804 kindreds, and (2) clarify therapeutic options in children.

METHODS

Thirty-eight members from five c804 kindreds underwent genetic analysis. Biochemical, operative, and pathology reports were reviewed.

RESULTS

Twenty-three gene carriers were identified, of whom 14 had thyroidectomy. Medullary thyroid carcinoma was found in 7 patients (aged 5-56 years), C-cell hyperplasia in 6 patients (aged 13-40 years), and normal histology in a single patient (aged 27 years). One patient with medullary thyroid carcinoma died of metastases (aged 12 years). Nine of the 23 gene carriers delayed operation, 4 of whom had calcitonin testing. Three of the 4 patients had abnormal calcitonin levels and a single patient was negative (aged 40 years). Of the remaining 9 patients, 2 await thyroidectomy, and 3 have refused evaluation.

CONCLUSIONS

Penetrance of the c804 mutation is highly variable. Medullary thyroid carcinoma associated with this genotype has aggressive potential. Prophylactic thyroidectomy in childhood is a viable approach.

A codon 891 exon 15 RET proto-oncogene mutation in familial medullary thyroid carcinoma: a detection strategy

A ser891ala RET proto-oncogene mutation has been previously discovered in a single kindred with familial medullary thyroid carcinoma (FMTC). An additional two probands with this mutation and with medullary thyroid carcinoma (MTC) without any other manifestations of MEN 2 have been identified. In one of thse families, two other individuals also had the mutant sequence and FMTC. Analysis of both cases showed cosegregation of the mutation and MTC. To facilitate detection of this mutation, a primer was engineered which creates a Hha I recognition site in the presence of the mutant sequence. As a result, this codon 891 exon 15 mutation can be identified with a restriction enzyme digestion.

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.

Oncogenic RET receptors display different autophosphorylation sites and substrate binding specificities

The c-ret proto-oncogene encodes a receptor tyrosine kinase which plays an important role in neural crest as well as kidney development. Genetic studies have demonstrated that germ line mutations in the ret oncogene are the direct cause of multiple endocrine neoplasia (MEN) 2A and 2B, familial medullary thyroid carcinoma (FMTC), and Hirschsprung's disease. However, despite the large body of genetic and biological evidence suggesting the importance of RET in development and neoplastic processes, the signal transduction mechanisms of RET remain unknown. To begin to understand the molecular mechanisms of the disease states caused by mutations in RET, the patterns of autophosphorylation of the wild-type RET and the MEN mutants were studied using site-directed mutagenesis and phosphopeptide mapping. Among the 6 autophosphorylation sites found in the wild-type RET receptor, the MEN2B mutant lacked phosphorylation at Tyr-1096, leading to decreased Grb2 binding, while simultaneously creating a new phosphorylation site. These changes in autophosphorylation suggest that the MEN2B mutation may result in the more aggressive MEN2B phenotype by altering the receptor's signaling capabilities.

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.

Expression of papillary thyroid carcinoma in multiple endocrine neoplasia type 2A

BACKGROUND

The ret protooncogene (RET), shown to be rearranged in human papillary thyroid cancers (PTC), has been mapped by in situ hybridization to 10q11.2 near the predisposition locus for the inherited cancer syndrome multiple endocrine neoplasia type 2 (MEN 2). To date PTC has not been an observed characteristic of MEN 2; however, linkage studies in affected families have shown no meiotic recombinants between the MEN 2A gene and RET suggesting tight linkage between loci. Furthermore, RET appears to be expressed in medullary thyroid carcinoma (MTC) and pheochromocytoma and for these reasons has emerged as a candidate gene for MEN 2.

METHODS

Two patients from a single kindred with MEN 2A (18 affected) are presented in which expression of PTC appeared to cosegregate with the MEN2 gene. In both patients the diagnosis of occult C-cell disease was suspected by an elevation in the basal and pentagastrin-stimulated peak calcitonin levels. Histologic examination of the thyroid gland after operation for MTC revealed tumor nodules consistent with PTC. There was no history of radiation exposure. Characteristics of MEN 2A syndrome in the kindred in addition to MTC and PTC include hyperparathyroidism and Hirschsprung's disease in three and two patients, respectively.

RESULTS

Two-point linkage analysis with a new highly polymorphic DNA marker, LGfd01, derived from a cosmid clone mapping to 10q11.2 assigns the MEN 2 predisposition locus in this kindred to chromosome 10q11.2 (0 = 0.00; maximum LOD, 4.78). Recombination between MEN 2A and a polymorphic microsatellite from the RET locus could not be shown among informative meioses.

CONCLUSIONS

The observed association of MEN 2A and PTC is intriguing and suggests that the variation in expression of the syndrome may be due to the presence of a structural alteration affecting several contiguous genes spanning the putative MEN 2 region.

Molecular genetics of APUDomas

It is tempting to speculate that genetic studies of the human APUDomas, particularly those of a hereditary nature, may ultimately provide valuable clues to the molecular basis of malignant transformation in cells of all types, uncover the mechanisms responsible for tumor progression, and perhaps decipher the signals important in the differentiation of normal neural crest-derived tissue. Generally, several strategies have been used in the genetic analysis of these tumors with success. These include (1) cytogenetic examination of recurring chromosomal abnormalities in hopes of pinpointing critical neighboring growth regulatory sequences important in tumor evolution, (2) identification of dominant acting oncogenes in tumor cells, (3) search for recessive inactivated suppressor genes that may regulate cell growth by analyzing tumors for loss of heterozygosity (LOH), and (4) genetic linkage studies of kindreds affected with familial APUDomas to identify and subsequently characterize the predisposition gene using a positional or functional cloning approach. The results of these strategies as they have been employed in the investigation of cutaneous malignant melanoma (CMM), the dysplastic nevus syndrome (DNS), and the multiple endocrine neoplasia (MEN) syndromes are summarized.

Long-term follow-up of a large North American kindred with multiple endocrine neoplasia type 2A

BACKGROUND

Sixty-one patients with multiple endocrine neoplasia (MEN) type 2A (27 men; 34 women; mean age, 39 years) from a single kindred (76 affected, 49 at risk) were followed 1 month to 33 years (median, 14 years) after diagnosis for disease expression.

METHODS

Peripheral basal and pentagastrin-stimulated calcitonin, parathyroid hormone, and calcium levels were measured in 60 patients, 58 of whom had undergone previous thyroidectomy; the calcitonin concentration in four patients was concomitantly determined in the hepatic and internal jugular veins. Biochemical or radiographic screening for pheochromocytoma was performed in 58 patients.

RESULTS

Recurrence of medullary thyroid carcinoma (MTC) developed in nineteen (33%) of 58 patients after they underwent thyroidectomies. In 14 of 19 patients regional metastases were inapparent at initial operation, and lymphadenectomy was not undertaken. Three patients underwent neck reexploration with removal of micrometastases after selective venous studies were performed. One patient, 33 years of age, died of MTC, and two patients who refused thyroidectomy are alive at 76 and 83 years of age. Fifteen patients are alive with disease 8 to 33 years after they underwent thyroidectomies. All patients identified by prospective screening remain pentagastrin negative. Pheochromocytoma developed in six patients (10%), and four patients have Hirschsprung's disease. Hyperparathyroidism was present in seven patients and did not occur in those with minimal MTC.

CONCLUSIONS

These observations suggest that (1) the course of MTC in MEN 2A is highly variable, (2) early treatment of C-cell disease can be curative, (3) routine lymphadenectomy for occult micrometastases may be necessary for cure of MTC, and (4) the hyperparathyroidism of MEN 2A may not be a primary genetic event.

Linkage mapping of human chromosome 10 microsatellite polymorphisms

Ten microsatellite DNA polymorphisms located on human chromosome 10 were regionally mapped using subchromosomal somatic cell hybrids and linkage analysis. The resulting order of the markers from pter-qter was [D10S89, D10S111], D10S107, D10S109, [D10S91, D10S110, D10S108, D10S88, D10S168], and D10S169. Order of the markers within brackets was uncertain, although the order given was most likely. The microsatellites were distributed along the chromosome from the proximal p arm to near qter, with an unlinked gap between D10S168 and D10S169.

Eastern Cooperative Oncology Group study 1879: mitotane and adriamycin in patients with advanced adrenocortical carcinoma

From November 1979 to July 1986, 52 patients (27 women and 25 men; median age 52 years) with advanced adrenocortical carcinoma entered a prospective, nonrandomized study evaluating moderate-dose mitotane and doxorubicin hydrochloride (Adriamycin). Thirty-two tumors (62%) were well differentiated and evidence of hormone production was present in 24 patients (46%). Patients with well-differentiated or functional tumors received mitotane, 6 gm daily; patients for whom mitotane failed or those with poorly differentiated, non-hormone-producing tumors received Adriamycin, 60 mg/m2 every 3 weeks. Initially, 36 patients were treated with mitotane and 16 patients with Adriamycin. Eight patients (22%) responded to mitotane and three (19%) responded to Adriamycin. No response was noted in the 15 patients for whom mitotane failed and who then received Adriamycin. Severe toxicity occurred in 36% of patients who received mitotane and in 26% who received Adriamycin. Overall median survival after onset of treatment was 14 months. We conclude that mitotane or Adriamycin used initially can induce tumor regression in about 22% and 19% of selected patients, respectively. However, Adriamycin is ineffective as second-line chemotherapy for patients with well-differentiated or functioning tumors for whom mitotane is ineffective.

Adrenocortical carcinoma

Ten patients, seven women and three men, ages 47 to 76 years (mean 58.6 years), treated for adrenal cortical carcinoma between 1971 and 1989, were reviewed. Three (30%) of the tumors were nonfunctioning. The remaining seven (70%) were functioning, six of them occurring in women. Common presenting features were hormonal excess, distant metastases, weight loss, and abdominal pain. The primary tumor was resected in all patients, only two of whom had disease confined to the adrenal gland. Tumor diameter ranged from 9 to 21 cm (mean 15.7 cm). Inferior vena caval or right atrial extension of tumor thrombus was present in two patients. Excluding two deaths from postoperative complications, seven patients died of their disease after a mean survival of 25 months (range 2 to 84 months). Of seven patients who received o,p'-DDD treatment for metastatic or recurrent tumor, three (43%) had an objective response. In two patients, tumor regression was complete and was associated with prolonged survival. The first patient underwent resection of recurrent tumor on two occasions in addition to receiving o,p'-DDD and survived 84 months. The second patient had complete regression of pulmonary and liver metastases confirmed at laparotomy and thoracotomy and remains free of disease at 78 months. None of the five patients treated with various combinations of cytotoxic chemotherapy had an observable response, and no measurable effect was seen in a single patient following abdominal radiotherapy. It is concluded that resection for local recurrence may prolong survival and that significant and lasting tumor regression is possible with o,p'-DDD administration. Beneficial results from cytotoxic agents, however, could not be demonstrated.

Evaluation of children with multiple endocrine neoplasia type IIb following thyroidectomy

Medullary thyroid carcinoma (MTC) develops in all patients with multiple endocrine neoplasia type IIb (MEN IIb), a rare syndrome that either occurs sporadically or is inherited in an autosomal dominant pattern. The MTC in patients with MEN IIb has been reported to be biologically aggressive with onset at a young age and rapid progression as evidenced by widespread metastases and death, frequently in the teenage years. Seven children, aged 2 to 11 years (mean, 7 years), from three kindreds with MEN IIb were evaluated for evidence of tumor recurrence 3 to 10 years following thyroidectomy. In one child, age 11, a thyroid mass was palpable preoperatively. However, in the remaining six children (aged 2 to 10 years), the diagnosis of MTC was established by an increased concentration of plasma calcitonin (CT), either basally or following pentagastrin (Pg) stimulation. All patients underwent total thyroidectomy with removal of central lymph nodes from the neck. At the time of surgery, six children were found to have bilateral macroscopic MTC, five without and one with cervical metastases. One child (age 2 years) had C-cell hyperplasia, a premalignant precursor of MTC. Currently, five of the seven children are without evidence of recurrent disease clinically and have normal plasma CT levels (less than 0.3 ng/mL) following calcium (Ca) and Pg stimulation 3, 3, 10, 10, and 10 years after thyroidectomy. Two of the seven children have biochemical evidence of residual MTC.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple endocrine neoplasia

The MEN syndromes continue to be the focus of considerable interest and research. Since successful treatment requires early diagnosis, proper screening and follow-up of patients at risk is important. In the individual at risk for developing MEN IIa, annual screening should include measurement of the basal and stimulated plasma CT levels, and determination of plasma levels of calcium, PTH, and CEA. Twenty-four hour urine excretion rates of norepinephrine, epinephrine, metanephrine, dopamine, and VMA should also be obtained. It is our recommendation that this screening be continued through the third decade of life. Patients having thyroidectomy for MTC need to be tested annually for recurrent MTC and the development of adrenal medullary disease. All patients at risk for developing MEN IIb should be evaluated in a similar fashion. Recently, several groups using DNA linkage analysis have mapped the gene for MEN IIa to chromosome 10, although the exact location of the gene is yet to be determined. Preliminary linkage studies have mapped the gene for MEN I to chromosome 11. The identification of the genes for MEN I and MEN II will greatly simplify the diagnosis of the disease and perhaps also the therapy of affected patients.

Intestinal filtration-secretion due to increased intraluminal pressure in rabbits

The mechanism of changes in small intestinal transport due to acutely increased intraluminal hydrostatic pressure (IHP) was investigated in detail using perfused in vivo rabbit intestinal segments. IHP affected passive transport in vivo by increasing effective mucosal surface area in the small intestine (indicated by 3HOH transport and tissue architectural changes) and increasing small intestinal permeability (indicated by a proportionately greater increase in mannitol than erythritol secretory clearance). IHP did not alter ileal blood flow rate measured by radioactive microspheres, despite grossly evident venous dilatation, or active intestinal transport in the ileum as measured by a) in vitro ion transport in the absence of elevated hydrostatic pressure, b) mucosal adenylate cyclase or Na-K-ATPase activities, and c) glucose-stimulated water and electrolyte absorption. Acutely increased IHP appears to influence the hydrodynamics of the mucosal microcirculation in the rabbit ileum to produce a driving force for passive filtration-secretion, which is associated with and possibly augmented by increased tissue permeability and effective surface area.

Cellular mechanisms of ion transport associated with osmotic gradients in rat small intestine

1. The electrical potential difference, short-circuit current, tissue conductance, and fluxes of sodium and chloride were measured in rat small intestine in an in vitro chamber preparation in the presence and absence of 100 mM-mannitol on either the mucosal or serosal surface. 2. Mucosal mannitol generally decreased potential difference, short-circuit current, and tissue conductance while serosal mannitol increased the electrical variables. 3. Mucosal mannitol decreased unidirectional movement of sodium and chloride but did not change the net transport of these ions. The change in short-circuit current was therefore ascribed to changes in fluxes of ions other than sodium and chloride. 4. Serosal mannitol increased the unidirectional fluxes of sodium, but not the new transport of this ion. The transport of chloride increased only in the serosal to mucosal direction yielding a net secretion of chloride equal to the change in short-circuit current. 5. The changes in potential difference and short-circuit current caused by mucosal mannitol were dependent on the presence of sodium. The changes due to serosal mannitol were dependent on both sodium and chloride. 6. Changes in undirectional transport of ions, small non-electrolytes, and water due to an osmotic gradient were attributed to changes in the dimension of the lateral intercellular spaces observed in earlier studies. 7. No evidence suggesting that the electrical changes due to the mannitol gradients could be attributed to diffusive or convective flows of fluid, but instead the changes were ascribed to perturbations in the cellular transport mechanisms.

Effects of methylprednisolone on electrolyte transport by in vitro rat ileum

Administration of the glucocorticoid methylprednisolone (MP) (30 mg/kg body wt for 3 days) to rats increased intestinal mucosal guanylate cyclase and Na-K-ATPase activities, short-circuit current (Isc), electrical potential difference (PD), net Na absorption, and net Cl secretion and reversed HCO3 transport from secretion to absorption. In the MP-treated animals, removal of HCO3 from both the mucosal and serosal bathing solutions increased Cl secretion but did not alter the Isc, PD, and net Na flux. Removal of Cl abolished the MP-induced increase in Isc but did not affect the MP-induced changes in net Na and HCO3 fluxes. At 6 h, after a single dose of MP, stimulation of guanylate cyclase activity was already maximal, whereas Na-K-ATPase activity was not detectably altered. The changes in intestinal transport properties present 6 h after MP treatment and associated with the increased guanylate cyclase activity were an increase in Isc and PD and a reversal of net Cl absorption to net secretion. These results suggest that an initial response to MP administration is a persistent increase in intestinal guanylate cyclase activity that mediates an electrogenic Cl secretory process, then is followed by a superimposed effect of increased Na-K-ATPase activity that mediates an increase in net Na absorption.

Mechanisms of electrolyte transport in rat ileum

The short-circuit current (Isc), potential difference (PD), tissue conductance (Gt), and Na and Cl fluxes in the short-circuit state across rat ileum were studied in Ussing chambers using a variety of bathing solutions. In Ringer solution, Isc exceeded net Na absorption and net Cl secretion occurred. Addition of 10 mM glucose increased Isc, PD, Gt, and net Na absorption, which accounts for 70% of the increase in Isc. Removal of HCO3 from Ringer solution did not alter any parameters but increased net Cl secretion due to a decrease in mucosal-to-serosal Cl flux. Reduction by 50% of the [Cl] in HCO3-free solution decreased the net Cl secretion to the level in Ringer solution and increased net Na absorption. Removal of Cl decreased Isc to the value of the net Na absorption and decreased the Na influx across the mucosal membrane by 39%. Isc and PD were near zero and net Cl absorption was observed in a Na-free solution. These results are consistent with the transport mechanism that consists of 1) an electrogenic Na absorptive process that accounts for the Isc, 2) a neutral NaCl-coupled secretory process, and 3) a system by which HCO3- secretion exchanges for Cl- absorption.

Enterolithiasis in a confined Hartman's mountain zebra

Enterolithiasis was observed on necropsy of a Hartman's mountain zebra (Equus zebra hartmannae). A single enterolith had caused obstruction and rupture of the small colon. The gross lesions are described and the possible etiology discussed.