The tumor susceptibility gene TMEM127 is mutated in renal cell carcinomas and modulates endolysosomal function.

TMEM127 is an endosome-associated tumor suppressor gene in pheochromocytomas, neuroendocrine tumors that can co-occur with renal cell carcinomas (RCCs). TMEM127 loss leads to increased mTOR signaling. However, the spectrum of tumors with TMEM127 mutation and how TMEM127 and mTOR interact in tumorigenesis remains unknown. Here, we report that germline TMEM127 mutations occur in RCCs and that some mutant proteins, unlike wild-type (WT) TMEM127, fail to cooperate with activated early endosomal GTPase, Rab5, to inhibit mTOR signaling. Tmem127-null mouse embryonic fibroblasts (MEFs) are deficient in generating early-to-late hybrid endosomes upon constitutive Rab5 activation, a defect rescued by WT, but not mutant, TMEM127. This endosomal dysfunction results in diminished mTOR colocalization with Rab5-positive vesicles. Conversely, active, lysosomal-bound mTOR is increased in Tmem127-null MEFs, which also display enhanced lysosomal biogenesis. Our data map the tumor-suppressive properties of TMEM127 to modulation of mTOR function in the endolysosome, a feature that may contribute to both pheochromocytoma and RCC pathogenesis.

Germline mutations of the PTEN gene in Cowden disease, an inherited breast and thyroid cancer syndrome.

Cowden disease (CD) is an autosomal dominant cancer predisposition syndrome associated with an elevated risk for tumours of the breast, thyroid and skin. Lhermitte-Duclos disease (LDD) cosegregates with a subset of CD families and is associated with macrocephaly, ataxia and dysplastic cerebellar gangliocytomatosis. The common feature of these diseases is a predisposition to hamartomas, benign tumours containing differentiated but disorganized cells indigenous to the tissue of origin. Linkage analysis has determined that a single locus within chromosome 10q23 is likely to be responsible for both of these diseases. A candidate tumour suppressor gene (PTEN) within this region is mutated in sporadic brain, breast and prostate cancer. Another group has independently isolated the same gene, termed MMAC1, and also found somatic mutations throughout the gene in advanced sporadic cancers. Mutational analysis of PTEN in CD kindreds has identified germline mutations in four of five families. We found nonsense and missense mutations that are predicted to disrupt the protein tyrosine/dual-specificity phosphatase domain of this gene. Thus, PTEN appears to behave as a tumour suppressor gene in the germline. Our data also imply that PTEN may play a role in organizing the relationship of different cell types within an organ during development.

An update on the genetics of paraganglioma, pheochromocytoma, and associated hereditary syndromes.

Pheochromocytomas (PCCs) and paragangliomas (PGLs) are catecholamine-secreting tumors of neural crest origin. Once collectively known as the '10% tumor', based on the frequency of inherited forms of the disease, they are now referred to as the '10-gene tumor', based on the number of susceptibility genes identified to date. Most familial cases of pheochromocytoma and/or paraganglioma and 10-20% sporadic cases carry germline mutations in VHL, RET, NF1, SDHA, SDHB, SDHC, SDHD, SDHAF2, TMEM127, or MAX. The finding of somatic mutations in VHL and RET in an additional 10-15% of tumors has brought the proportion of all patients with PCC and/or PGL due to a genetic disruption in these genes to approximately one half. These findings impact on the clinical management of patients. The diversity in the genetic etiology has transcription correlates, which are reflected in the 2 main transcription signatures underlying these mutations: a pseudohypoxic cluster (VHL and SDH gene mutation carriers) and a cluster rich in kinase receptor signaling and protein translation pathways (RET, NF1, TMEM127 and MAX mutation carriers). Recognition of these clusters offers clues to better understand tumor pathogenesis as well as a rationale for the development of targeted therapies. In this report we provide an overview of the transcription-based classification of PCCs and PGLs, an update on the more recently identified susceptibility genes and an outline of current gaps in this research field as well as challenges for the coming years.

Pheochromocytomas: from genetic diversity to new paradigms.

Pheochromocytomas and paragangliomas are catecholamine-secreting tumors of neural crest origin caused by germline mutations in at least six distinct genes. This genetic heterogeneity has provided a rich source for both the discovery and functional characterization of new tumor-related genes. However, the genetic repertoire of these tumors is still not fully known, and current evidence points to the existence of additional pheochromocytoma susceptibility genes. Here, the unique contributions of three hereditary models of pheochromocytoma that can advance our knowledge of the disease pathogenesis are presented. The first model, loss of succinate dehydrogenase (SDH) function, illustrates how SDHB, C, or D mutations, components of the energy metabolism pathway, serve as a unique system to explore the pervasive metabolic shift of cancer cells towards glycolysis as a source of energy (also known as the Warburg effect) in contrast to the characteristic oxidative phosphorylation of normal cells. In the second model, mechanisms of tumorigenesis distinct from classical pheochromocytoma susceptibility genes are discussed in the context of a novel putative suppressor of neural crest-derived tumors, the KIF1B beta gene. Finally, NF1 loss is highlighted as a valuable study model to investigate the cell lineage selectivity of the Egln3-mediated developmental apoptotic defect of chromaffin precursor cells. Results from these studies may offer clues to understand the tissue specificity of hereditary pheochromocytoma syndromes. These distinct hereditary disease models illustrate how genetic-driven progress has the potential to narrow current gaps in our knowledge of pheochromocytoma and paraganglioma pathogenesis.

Mutation analysis of glial cell line-derived neurotrophic factor (GDNF), a ligand for the RET/GDNF receptor alpha complex, in sporadic phaeochromocytomas.

Phaeochromocytomas usually occur sporadically but may also be a feature of three autosomal dominantly inherited cancer syndromes, multiple endocrine neoplasia type 2, von Hippel-Lindau disease (VHL), and, very rarely, type 1 neurofibromatosis. Germ-line missense mutations in the RET proto-oncogene, which encodes a receptor tyrosine kinase, cause multiple endocrine neoplasia type 2. In VHL, germ-line mutations in one of the three exons of the VHL tumor suppressor gene have been found in the majority of families. Whereas somatic mutations in the VHL gene have been common in sporadic renal cell carcinoma, a component cancer of VHL, somatic mutations in the RET and VHL genes together have been found in approximately 10% of sporadic phaeochromocytomas. Hence, other genes must also contribute to the pathogenesis of sporadic phaeochromocytomas. Recent data have suggested that glial cell line-derived neurotrophic factor (GDNF) is a ligand for RET and acts via a heterotetrameric receptor complex that includes GDNF receptor alpha, which provides ligand binding capabilities, and RET, which provides the signaling component. Thus, both GDNF and GDNFR-alpha are plausible candidate genes for involvement in the pathogenesis of phaeochromocytomas. To investigate the role of GDNF in sporadic phaeochromocytomas, we scanned a panel of 22 tumors. Among these samples, only a conservative sequence variant was detected in exon 2 of GDNF. No disease-associated somatic GDNF mutations or gross gene amplification were detected in these tumors, suggesting only a minor role for GDNF in the genesis of phaeochromocytomas.

Somatic deletions and mutations in the Cowden disease gene, PTEN, in sporadic thyroid tumors.

The majority of familial medullary thyroid neoplasms are associated with germ-line mutations of the RET proto-oncogene, yet very little is known about the mechanisms involved in the pathogenesis of familial and sporadic nonmedullary thyroid tumors. A subset of thyroid tumors have loss of heterozygosity of chromosome 10q22-23, a region harboring the gene responsible for Cowden disease, an autosomal dominant hamartoma syndrome associated with thyroid and breast tumors. PTEN/MMAC1/TEP1 codes for a dual-specificity phosphatase and is likely a tumor suppressor gene. We sought to determine the PTEN status in a series of epithelial thyroid neoplasms. We studied 95 sporadic thyroid tumors, of which 39 were papillary thyroid carcinomas (PTCs), 12 were follicular carcinomas, 9 were anaplastic carcinomas, 5 were Hürthle cell carcinomas, 21 were nonfunctioning follicular adenomas, and 9 were Hürthle cell adenomas. Direct sequencing of PCR-amplified products was performed for all nine exons of PTEN. Two polymorphic markers, one located in intron 8 and another, a dinucleotide repeat marker, AFMa086wg9, located within intron 2, were analyzed in paired blood-tumor DNA samples to assess hemizygous deletions of PTEN. We found a somatic frameshift mutation in one PTC, which was expected to generate a premature stop codon 2 amino acids downstream. Twenty-six % of informative benign tumors (four follicular adenomas and three Hürthle cell adenomas) and only 3 of 49 (6.1%) informative malignant tumors (one PTC, one follicular carcinoma, and one anaplastic carcinoma) showed evidence of hemizygous deletion of PTEN (P = 0.046). We conclude that a subset of thyroid tumors have somatic deletions of the PTEN gene, predominantly the benign forms, and that small intragenic mutations of PTEN are infrequent in thyroid tumors. We speculate that other mechanisms of PTEN inactivation, rather than small intragenic mutations, might occur in the hemizygously deleted samples and act as the "Knudson second hit." Alternatively, other tumor suppressor genes mapping to chromosome 10q22-23 could be the actual targets for such deletions and thus represent the various hits in the pathway of multistep carcinogenesis.

PTEN suppresses breast cancer cell growth by phosphatase activity-dependent G1 arrest followed by cell death.

PTEN/MMAC1/TEP1, a tumor suppressor gene, is frequently mutated in a variety of human cancers. Germ-line mutations of phosphatase and tensin homolog, deleted on chromosome ten (PTEN) are found in two inherited hamartoma tumor syndromes: Cowden syndrome, which has a high risk of breast, thyroid, and other cancers; and Bannayan-Zonana syndrome, a related disorder. PTEN encodes a phosphatase that recognizes both protein substrates and phosphatidylinositol-3,4,5-triphosphate. The lipid phosphatase activity of PTEN seems to be important for growth suppression through inhibition of the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. We established clones with stable PTEN expression controlled by a tetracycline-inducible system to examine the consequences of increased levels of wild-type and mutant PTEN expression in a well-characterized breast cancer line, MCF-7. When we overexpressed PTEN in MCF-7, growth suppression was observed, but only if PTEN phosphatase activity is preserved. The initial growth suppression was attributable to G1 cell cycle arrest, whereas subsequent growth suppression was attributable to a combination of G1 arrest and cell death. Of note, the decrease in Akt phosphorylation preceded the onset-of suppression of cell growth. Treatment of MCF-7 cells with wortmannin, a PI3K inhibitor, caused cell growth inhibition in a way similar to the effects of overexpression of PTEN in this cell. In general, the inverse correlation between PTEN protein level and Akt phosphorylation was found in a panel of breast cancer cell lines. Therefore, PTEN appears to suppress breast cancer growth through down-regulating PI3K signaling, which leads to the blockage of cell cycle progression and the induction of cell death, in a sequential manner.

Exclusion of PTEN and 10q22-24 as the susceptibility locus for juvenile polyposis syndrome.

Juvenile polyposis syndrome (JPS; MIM 174900) is an autosomal dominant condition with incomplete penetrance characterized by hamartomatous polyps of the gastrointestinal tract and a risk of gastrointestinal cancer. Gastrointestinal hamartomatous polyps are also present in Cowden syndrome (CS; MIM 158350) and Bannayan-Zonana syndrome (BZS; also called Ruvalcaba-Myhre-Smith syndrome; MIM 153480). The susceptibility locus for both CS and BZS has recently been identified as the novel tumor suppressor gene PTEN, encoding a dual specificity phosphatase, located at 10q23.3. A putative JPS locus, JP1, which most likely functions as a tumor suppressor, had previously been mapped to 10q22-24 in both familial and sporadic juvenile polyps. Given the shared clinical features of gastrointestinal hamartomatous polyps among the three syndromes and the coincident mapping of JP1 to the region of PTEN, we sought to determine whether JPS was allelic to CS and BZS by mutation analysis of PTEN and linkage approaches. Microsatellite markers spanning the CS/BZS locus (D10S219, D10S551, D10S579, and D10S541) were used to compute multipoint lod scores in eight informative families with JPS. Lod scores of < -2.0 were generated for the entire region, thus excluding PTEN and any genes within the flanking 20-cM interval as candidate loci for familial JPS under our statistical models. In addition, analysis of PTEN using a combination of denaturing gradient gel electrophoresis and direct sequencing was unable to identify a germline mutation in 14 families with JPS and 11 sporadic cases. Therefore, at least a proportion of JPS cases are not caused by germline PTEN alteration or by an alternative locus at 10q22-24.

Mutation and expression analysis of the p27/kip1 gene in corticotrophin-secreting tumours.

The molecular mechanisms leading to Cushing's disease are unclear. Inhibitors of cyclin-cyclin dependent kinase (CDK) complexes are regulators of the cell cycle and may function as tumour suppressor genes, many of which have been involved in the pathogenesis of several human malignancies. A member of this family, the p27/kip1 gene, maps to chromosome 12p13 and encodes an inhibitor of several cyclin-CDK complexes; these control the progression of the cell cycle from G1 to S-phase. Complete lack of p27/kip1 function, as occurs in the p27/kip1 'knockout' mouse, produces a complex phenotype associated with the development of pituitary tumours, specifically those of the intermediate lobe corticotrophs. We therefore investigated whether structural and functional abnormalities of the p27/kip1 gene and loss at the chromosome 12p13 region were present in human corticotrophin (ACTH)-secreting pituitary tumours. We studied 21 pituitary tumours, of which 20 were ACTH-secreting (two of these had biochemical and histological features of 'intermediate-lobe' tumours and one was malignant) while the remaining tumour was a prolactinoma; three ectopic secretors of ACTH (two bronchial and one thymic carcinoid); and a non-secretory thymic carcinoid. The whole coding region of the p27/ kip1 gene was screened for mutations by PCR-SSCP analysis and/or direct sequencing, while tumour mRNA expression was analysed by means of a semi-quantitative duplex PCR. Three polymorphic microsatellite markers of the 12p13 region were used to assess loss of heterozygosity (LOH) in 12 samples. Finally, tumour p27/kip1 protein expression was assessed by immunohistochemistry using a monoclonal antibody in 12 samples suitable for analysis. No sequence abnormalities were found in any of the samples other than a previously-described polymorphism. No LOH was observed in the tumours analysed. p27/kip1 mRNA expression was similar in tumour samples in comparison with normal pituitaries. Seven of the eight corticotroph tumours analysed by immunohistochemistry stained positive for p27/kip1, including the intermediate lobe. The only malignant pituitary tumour in the original series showed an absence of staining for p27/kip1. In addition, the three carcinoid tumours studied were negative on immunohistochemistry. Of a further three malignant pituitary tumours assessed, two (including a prolactinoma) were essentially negative, while the third was moderately positive. We conclude that mutations of the p27/kip1 gene, deletions of the 12p13 area or changes in expression, are not a general feature of corticotroph tumours, even those with intermediate lobe characteristics. However, other mechanisms of p27/kip1 inactivation, such as an abnormality at the post-translational level, may be related to more aggressive histological subtypes of ACTH-secreting and possibly other pituitary tumours.

Somatic mitochondrial DNA (mtDNA) mutations in papillary thyroid carcinomas and differential mtDNA sequence variants in cases with thyroid tumours.

Somatic mutations in mtDNA have recently been identified in colorectal tumours. Studies of oncocytic tumours have led to hypotheses which propose that defects in oxidative phosphorylation may result in a compensatory increase in mitochondrial replication and/or gene expression. Mutational analysis of mtDNA in thyroid neoplasia, which is characterised by increased numbers of mitochondria and is also one of the most common sites of oncocytic tumours. has been limited to date. Using the recently developed technique of two-dimensional gene scanning, we have successfully examined 21 cases of thyroid tumours, six cases of non-neoplastic thyroid pathology, 30 population controls, nine foetal thyroid tissues and nine foetal tissues of non-thyroid origin, either kidney or liver. We have identified three different somatic mutations (23%) in papillary thyroid carcinomas. In addition, we have found significant differential distributions of mtDNA sequence variants between thyroid carcinomas and controls. Interestingly, these variants appear to be more frequent in the genes which encode complex I of the mitochondrial electron transport chain compared to normal population controls. These findings suggest first, that somatic mtDNA mutations may be involved in thyroid tumorigenesis and second, that the accumulation of certain non-somatic variants may be related to tumour progression in the thyroid.

Over-representation of a germline RET sequence variant in patients with sporadic medullary thyroid carcinoma and somatic RET codon 918 mutation.

The aetiology of sporadic medullary thyroid carcinoma is unknown. About 50% harbour a somatic mutation at codon 918 of RET (M918T). To investigate whether other RET sequence variants may be associated with or predispose to the development of sporadic medullary thyroid carcinoma, we analysed genomic DNA from the germline and corresponding tumour from 50 patients to identify RET sequence variants. In one patient, tumour DNA showed a novel somatic 12 bp in-frame deletion in exon 15. More interestingly, we found that the rare polymorphism at codon 836 (c.2439C > T; S836S) occurred at a significantly higher frequency than that in control individuals without sporadic medullary thyroid carcinoma (Fisher's exact test, P = 0.03). Further, among the nine evaluable cases with germline c.2439C/T, eight also had the somatic M918T mutation in MTC DNA which was more frequent than in patients with the more common c.2439C/C (89% vs 40%, respectively; Fisher's exact test, P = 0.01). These findings suggest that the rare sequence variant at codon 836 may somehow play a role in the genesis of sporadic medullary thyroid carcinoma.

A highly conserved processed PTEN pseudogene is located on chromosome band 9p21.

PTEN/MMAC1/TEP1, encoding a dual-specificity phosphatase, is a tumor suppressor gene which has recently been cloned and mapped to chromosome 10q23.3. We have shown that germline mutations of PTEN are present in individuals with two hamartoma syndromes: Cowden Syndrome, associated with a predisposition to breast and thyroid cancers, and Bannayan-Zonana syndrome. Somatic mutations of PTEN have been reported in a variety of human cancer cell lines, suggesting a potential role for this gene in the pathogenesis of human malignancies. We report the identification of a highly conserved PTEN processed pseudogene, psiPTEN, which shares over 98% homology with the coding region of functional PTEN, and its localisation to chromosome 9p21. The high sequence homology of psiPTEN with the PTEN transcript may potentially lead to misinterpretation when performing mutation analyses based on cDNA templates. Caution should be exerted when using such screening approaches.

PTEN, a unique tumor suppressor gene.

For many years, it has been thought that the chromosome region 10q22-24 includes one or more genes that appear to play a role in several human malignancies. PTEN is a new tumor suppressor gene encoding a dual-specificity phosphatase that was cloned simultaneously by three groups (Li & Sun 1997, Li et al. 1997, Steck et al. 1997), two of which used a positional cloning approach to identify genes in chromosome 10 (Li et al. 1997, Steck et al. 1997). While several protein kinases have been implicated as oncogenes, and phosphatases have long been known frequently to antagonize their function, there has been no direct demonstration of the role of phosphatases in tumor development (Myers & Tonks 1997). PTEN characterization as a bona fide tumor suppressor gene has confirmed that a deficient phosphatase activity can lead to cancer, as detailed by studies that are described below.

Analysis of the SDHD gene, the susceptibility gene for familial paraganglioma syndrome (PGL1), in pheochromocytomas.

Pheochromocytomas are neural crest-derived tumors that occur mostly sporadically, but may also be part of inherited syndromes. The molecular pathogenesis of sporadic pheochromocytomas remains unknown. Recently, the susceptibility gene for familial paraganglioma syndrome, a disorder embryologically related to pheochromocytomas, was characterized and shown to encode the small subunit of succinate dehydrogenase (SDHD), which is part of the mitochondrial complex II. This complex regulates oxygen-sensing signals. Importantly, hypoxic signals also appear to be related to the pathogenesis of pheochromocytomas associated with von Hippel-Lindau syndrome. We sequenced the entire coding region of the SDHD gene in a series of pheochromocytomas. Although we did not find mutations in the gene, we identified a new intronic single nucleotide polymorphism in 15% of the samples (g.97739A-->G). We also confirmed the existence of a sequence highly homologous to the SDHD complementary DNA in chromosome 1p34--36, a region commonly deleted in pheochromocytomas. Full analysis of this sequence revealed a heterozygous single base substitution in 70% of our samples that was also present in the germline. This sequence does not appear to be transcribed and is probably a processed pseudogene. Therefore, despite its chromosomal location, it is unlikely that this sequence is a target of loss of heterozygosity in pheochromocytomas. In conclusion, mutations of the SDHD gene are not a common event in this series of sporadic pheochromocytomas. The existence of SDHD pseudogenes should be considered when analyzing complementary DNA-based samples.

Somatic mutation and germline variants of MINPP1, a phosphatase gene located in proximity to PTEN on 10q23.3, in follicular thyroid carcinomas.

Various genes have been identified to play a role in the pathogenesis of follicular thyroid tumors. Cowden syndrome is the only known familial syndrome with an increased risk of both follicular thyroid adenoma (FA) and carcinoma (FTC). Germline mutations in the tumor suppressor gene PTEN, which encodes a dual-specificity phosphatase, have been found in up to 80% of patients with Cowden syndrome suggesting a role of PTEN in the pathogenesis of follicular thyroid tumors. Although somatic intragenic mutations in PTEN, which maps to 10q23.3, are rarely found in follicular tumors, loss of heterozygosity (LOH) of markers within 10q22-24 occurs in about 25%. Recently, another phosphatase gene, MINPP1, has been localized to 10q23.3. MINPP1 has the ability to remove 3-phosphate from inositol phosphate substrates, a function that overlaps that of PTEN. Because of this overlapping function with PTEN and the physical location of MINPP1 to a region with frequent LOH in follicular thyroid tumors, we considered it to be an excellent candidate gene that could contribute to the pathogenesis of follicular thyroid tumors. We analyzed DNA from tumor and corresponding normal tissue from 23 patients with FA and 15 patients with FTC for LOH and mutations at the MINPP1 locus. LOH was identified in four malignant and three benign tumors. One of these FTCs with LOH was found to harbor a somatic c.122C > T or S41L mutation. We also found two germline sequence variants, c.809A > G (Q270R) and IVS3 + 34T > A. The c.809A > G variant was found in only one patient with FA but not in patients with FTC or normal controls. More interestingly, IVS3 + 34T > A was found in about 15% of FA cases and normal controls but not in patients with FTC. These results suggest a role for MINPP1 in the pathogenesis of at least a subset of malignant follicular thyroid tumors, and MINPP1 might act as a low penetrance predisposition allele for FTC.

Expression of glucocorticoid receptor gene isoforms in corticotropin-secreting tumors.

The molecular basis of Cushing's disease is not known. One of the most characteristic features of such tumors is their resistance to corticosteroid feedback at the pituitary level. We have hypothesized that abnormalities of the glucocorticoid receptor (GR) gene might play a role in the development of Cushing's disease via an increase in the relative production of the nonligand-binding splice variant of the GR, GR beta, known to exert dominant negative effects over the ligand-binding isoform, GR alpha. Alternatively, a change in overall GR expression, or mutations of some functional domains of the GR gene, might be involved in the pathogenesis of corticotroph tumors. We studied 22 tumors (17 pituitary ACTH-secreting tumors, 2 ectopic ACTH-producing tumors, 2 prolactinomas, and 1 nonfunctioning adenoma) and three normal pituitaries. RT-PCR was performed with primers specific to GR alpha and GR beta complementary DNA, followed by Southern blotting using an internal probe, and the ratio of the two bands quantitated by densitometry. We also assessed the overall expression of GR relative to the message of both the POMC gene and a housekeeping gene. Single-strand conformation polymorphism analysis of the DNA-binding domain and splice junction region of the gene was also performed. GR alpha messenger RNA was expressed at 37.3-fold +/- 5.7 (range, 32 to 46) excess, as compared with the GR beta subform. This pattern was observed both in the tumor samples and in the normal pituitaries used as controls. A majority of the ACTH-secreting tumors (16/19), including the ectopic secretors, showed variable but increased overall GR expression, whereas 3 tumors showed an expression approximately equivalent to the normal controls; however, no correlation was found between these two groups and the response to the high-dose dexamethasone test, nor was there any correlation with tumor histology. No mutations were found in any of the tumors by PCR-single-strand conformation polymorphism analysis. In conclusion, although both pituitary and ectopic ACTH-secreting tumors are at least partially glucocorticoid-resistant, no significant abnormalities in the relative expression of the two main GR subforms were observed in a series of such tumors. Additionally, mutations of regions critical to normal function of the receptor do not seem to be a frequent event in these tumors.

An inactivating mutation of the luteinizing hormone receptor causes amenorrhea in a 46,XX female.

Hypergonadotropic hypogonadism is characterized by decreased gonadal function due to the inability of the gonads to respond to pituitary gonadotropins. Hypergonadotropic hypogonadism in females has many causes, among which are ovarian dysgenesis and abnormalities of the ovarian receptors for the pituitary gonadotropins. We evaluated a woman who presented with amenorrhea due to hypergonadotropic hypogonadism, but who had structurally normal ovaries. She is a sister of two previously identified 46,XY male pseudohermaphrodites with Leydig cell hypoplasia. Injection of hCG did not cause any change in plasma levels of estradiol or progesterone, suggesting complete ovarian resistance to LH. Analysis of the DNA sequence of the LH receptor gene revealed that the patient is homozygous for the same single base change as her two brothers. This mutation causes substitution of an alanine residue by a proline at position 593. In vitro analysis of the mutant LH receptor in cultured human embryonic kidney 293 cells documented that the receptor is unable to stimulate adenylyl cyclase in response to hCG. Plasma levels of estradiol and progesterone were low, whereas LH and FSH levels were increased. On histological analysis of the ovary, follicles were seen at all developmental stages. Nonetheless, primary amenorrhea had been present for 5 yr, and repeated measurements of plasma estradiol and progesterone indicate that ovulation does not occur. These results document the existence of inherited LH resistance as a cause of primary amenorrhea in women. The combined clinical and molecular observations are consistent with previous experimental data suggesting that in humans, LH is necessary for ovulation but follicular maturation can occur in the presence of FSH alone.

Germline dinucleotide mutation in codon 883 of the RET proto-oncogene in multiple endocrine neoplasia type 2B without codon 918 mutation.

The autosomal dominant multiple endocrine neoplasia type 2 syndromes (MEN 2) comprise three clinically distinct entities, MEN 2A, familial medullary thyroid carcinoma and MEN 2B, which share a common clinical feature: medullary thyroid carcinoma (MTC). MEN 2B is considered to have the most aggressive form of MTC. Therefore, early detection of MEN 2B in order to prevent potentially lethal MTC is important. More than 95% of all MEN 2B cases are caused by germline mutation at codon 918 (M918T) in exon 16 of the RET proto-oncogene. In this study, we demonstrate the presence of germline codon 883 mutation (A883F) in 2 of 3 unrelated MEN 2B cases without codon 918 mutation. Our data demonstrate a novel etiologic event which may have roles in predisposition to MEN 2B when present in the germline and in the pathogenesis of sporadic MTC when somatic.

Vasopressin receptor expression and mutation analysis in corticotropin-secreting tumors.

Vasopressin is an important regulator of hypothalamo-pituitary-adrenal axis activation, primarily acting through the V3 receptor (V3R). Many patients with ACTH-secreting pituitary adenomas, but not normal individuals, respond to desmopressin, a relatively V2-specific vasopressin agonist, with increased ACTH and cortisol levels. We have searched for mutations of the V3R gene in ACTH-secreting pituitary adenomas and one ectopic ACTH-secreting tumor. No abnormalities were found in 12 tumors studied by PCR-single strand conformation polymorphism (PCR-SSCP) analysis. We then verified by RT-PCR whether the response to desmopressin was due to overexpression of the V3R or abnormal expression of the V2R in the pituitary tumor. We found that the V2R gene was expressed in a number of corticotroph tumors and in the ACTH-secreting ectopic tumor, and that the V3R gene appears to be overexpressed in these tumors. We conclude that V3R mutations are unlikely to be present in the ACTH-secreting tumors we examined, but that the V2R gene is expressed in the majority of the samples tested, and the V3R is expressed in all of these tumors. We speculate that the response to the desmopressin test observed in patients with Cushing's disease may be due to abnormal expression of V3R or V2R in ACTH-secreting tumors.