Familial acromegaly: a specific clinical entity--further evidence from the genetic study of a three-generation family

The AIP (aryl hydrocarbon receptor-interacting protein) gene and its relation to the pathogenesis of pituitary adenomas

Pituitary adenomas are monoclonal neoplasms that may secrete excessive quantities of their endogenous hormones, or may not be associated with any obvious syndrome, in which case they are known as non-functioning pituitary adenomas. Around 2 % have been said to occur in a familial setting, in the absence of any other tumor, now described as familial isolated pituitary adenomas (FIPA). Some 15-30 % of such families harbor inactivating germ-line mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene, along with 20 % of pediatric seemingly sporadic cases. AIP mutants are referred to as having pituitary adenoma predisposition, and present with early onset, aggressive macroadenomas, most of which secrete somatotropin. Evidence from transfection studies implies that AIP acts as a tumor suppressor; although whether this is mediated through an interaction with the aryl hydrocarbon receptor, phosphodiesterases, or with cell cycle regulators such as survivin or RET remains controversial. However, at present an interaction with the cyclic AMP pathway seems most plausible. Recently, evidence has shown that AIP may act at the cell surface, causing changes in integrin function. The presence of AIP mutations in a significant proportion of FIPA families as well as in apparently sporadic cases, particularly in young patients, suggests a need to screen such patients for AIP mutations to enable better clinical management. However, the absence of AIP mutations in over half of such cases highlights the need to search for further gene mutations.

cAMP in the pituitary: an old messenger for multiple signals

The cyclic nucleotide cAMP is a universal regulator of a variety of cell functions in response to activated G-protein coupled receptors. In particular, cAMP exerts positive or negative effects on cell proliferation in different cell types. As demonstrated by several in vitro studies, in somatotrophs and in other endocrine cells, cAMP is a mitogenic factor. In agreement with this notion, it has been found that the mutations of genes coding for proteins that contribute to increases in the cAMP signaling cascade may cause endocrine tumor development. This review will discuss the central role of cAMP signaling in the pituitary, focusing on the cAMP pathway alterations involved in pituitary tumorigenesis, as well as on poorly investigated the aspects of cAMP cascade, such as crosstalk with the ERK signaling pathway and new cAMP effectors.

Familial isolated pituitary adenomas (FIPA) and the pituitary adenoma predisposition due to mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene

Pituitary adenomas are one of the most frequent intracranial tumors and occur with a prevalence of approximately 1:1000 in the developed world. Pituitary adenomas have a serious disease burden, and their management involves neurosurgery, biological therapies, and radiotherapy. Early diagnosis of pituitary tumors while they are smaller may help increase cure rates. Few genetic predictors of pituitary adenoma development exist. Recent years have seen two separate, complimentary advances in inherited pituitary tumor research. The clinical condition of familial isolated pituitary adenomas (FIPA) has been described, which encompasses the familial occurrence of isolated pituitary adenomas outside of the setting of syndromic conditions like multiple endocrine neoplasia type 1 and Carney complex. FIPA families comprise approximately 2% of pituitary adenomas and represent a clinical entity with homogeneous or heterogeneous pituitary adenoma types occurring within the same kindred. The aryl hydrocarbon receptor interacting protein (AIP) gene has been identified as causing a pituitary adenoma predisposition of variable penetrance that accounts for 20% of FIPA families. Germline AIP mutations have been shown to associate with the occurrence of large pituitary adenomas that occur at a young age, predominantly in children/adolescents and young adults. AIP mutations are usually associated with somatotropinomas, but prolactinomas, nonfunctioning pituitary adenomas, Cushing disease, and other infrequent clinical adenoma types can also occur. Gigantism is a particular feature of AIP mutations and occurs in more than one third of affected somatotropinoma patients. Study of pituitary adenoma patients with AIP mutations has demonstrated that these cases raise clinical challenges to successful treatment. Extensive research on the biology of AIP and new advances in mouse Aip knockout models demonstrate multiple pathways by which AIP may contribute to tumorigenesis. This review assesses the current clinical and therapeutic characteristics of more than 200 FIPA families and addresses research findings among AIP mutation-bearing patients in different populations with pituitary adenomas.

Where is the culprit? A case of acromegaly that defied the management algorithm

A 30-year-old Filipino man presented with a 11-year history of coarse facial features and progressive enlargement of hands and feet. Initial work-up revealed elevated insulin-like growth factor-1 and non-suppressible growth hormone level after 75 g glucose challenge test. Initial cranial MRI performed in the year 2010 showed absence of pituitary adenoma. The patient was lost to follow-up. He again consulted in the year 2011 and a repeat cranial MRI and a dedicated pituitary MRI were performed and both did not reveal any pituitary mass. Further investigation included chest and abdominal CT scan, both of which did not show any neoplasm. At present, there has been no practice guideline on the management of acromegalic patients on whom the identifiable source cannot be found. The patient was given the option to undergo surgical exploration of the pituitary gland or medical treatment with somatostatin analogues. He decided to undergo surgery but has not given consent for the procedure.

Genetic analysis in a patient presenting with meningioma and familial isolated pituitary adenoma (FIPA) reveals selective involvement of the R81X mutation of the AIP gene in the pathogenesis of the pituitary tumor

Familial isolated pituitary adenoma (FIPA), defined as the occurrence of at least two cases of pituitary adenoma in a family that does not exhibit features of syndromic diseases, such as Carney complex or Multiple Endocrine Neoplasia type 1 or 4, is a rare autosomal dominant disease with low penetrance. About 20 % of the families with FIPA harbor inactivating mutation in aryl hydrocarbon receptor-interacting protein gene (AIP) associated with loss of heterozygosity of the same genetic locus (11q13) in the tumor. Rarely different types of extra-pituitary tumors have been described in the setting of AIP mutation-positive FIPA. We present the case of a patient who was diagnosed with acromegaly due to the AIP mutation c.241C>T (p.R81X) at the age of 34 years, and treated by transsphenoidal surgery. At the age of 43 years she was diagnosed with a meningioma, and at age 46 had recurrence of the somatotropinoma. Genetic studies demonstrated loss of the normal allele (by sequencing and microsatellite analysis) in DNA from the pituitary adenoma but not from the meningioma, suggesting a selective involvement of AIP mutation in the pathogenesis of the pituitary adenoma, and a casual association with the meningioma. Further investigations are required to define the exact role of AIP in non-pituitary tumorigenesis.

Familial gigantism

Familial GH-secreting tumors are seen in association with three separate hereditary clinical syndromes: multiple endocrine neoplasia type 1, Carney complex, and familial isolated pituitary adenomas.

Familial isolated pituitary adenomas experience at a single center: clinical importance of AIP mutation screening

We present four FIPA kindred discussing clinical and molecular data and emphasizing the differences regarding AIP status, as well as the importance of genetic screening. Family 1 consists of five patients harboring somatotropinomas with germline E24X mutation in AIP. In one of the patients, acromegaly was diagnosed through active screening, being cured by surgery. Families 2 and 3 are composed of two patients with non-functioning pituitary adenomas. Family 4 comprises patients harboring a prolactinoma and a somatotropinoma. No mutations in AIP were found in these families. No patient in Family 1 was controlled with octreotide treatment, while the acromegalic patient in Family 4 was controlled with octreotide LAR. In conclusion, FIPA is a heterogeneous condition, which may be associated with AIP mutation. Genomic and clinical screening is recommended in families with two or more members harboring pituitary adenomas, allowing early diagnosis and better outcome.

AIP and its interacting partners

Germline mutations in the aryl hydrocarbon receptor-interacting protein gene (AIP) predispose to young-onset pituitary tumours, most often to GH- or prolactin-secreting adenomas, and most of these patients belong to familial isolated pituitary adenoma families. The molecular pathway initiated by the loss-of-function AIP mutations leading to pituitary tumour formation is unknown. AIP, a co-chaperone of heat-shock protein 90 and various nuclear receptors, belongs to the family of tetratricopeptide repeat (TPR)-containing proteins. It has three antiparallel α-helix motifs (TPR domains) that mediate the interaction of AIP with most of its partners. In this review, we summarise the known interactions of AIP described so far. The identification of AIP partners and the understanding of how AIP interacts with these proteins might help to explain the specific phenotype of the families with heterozygous AIP mutations, to gain deeper insight into the pathological process of pituitary tumour formation and to identify novel drug targets.

Role of the aryl hydrocarbon receptor-interacting protein in familial isolated pituitary adenoma

Pituitary adenomas are typically sporadic benign tumors. However, approximately 5% of cases have been found to be familial in origin. Of these, approximately 40% occur in the absence of multiple endocrine neoplasia type 1 or Carney complex and have been termed 'familial isolated pituitary adenoma' (FIPA). Recently, germline mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene have been described in 15-20% of these families, identifying an autosomal dominant condition with incomplete penetrance termed 'pituitary adenoma predisposition'. Pituitary adenoma predisposition cohorts show a marked disposition to develop large, aggressive somatotroph, somatolactotroph or lactotroph adenomas, typically presenting at a young age. AIP mutation families have a distinct clinical phenotype compared with AIP mutation-negative FIPA families. Current evidence suggests that AIP is a tumor-suppressor gene. AIP has been demonstrated to interact with a number of cellular proteins, including several nuclear receptors, heat-shock protein 90 and survivin, although the mechanism of the tumor-suppressor effect is unknown. This article summarizes available data regarding the role of AIP in pituitary tumorigenesis and the clinical features of FIPA.

Molecular genetics of the aip gene in familial pituitary tumorigenesis

Pituitary adenomas usually occur as sporadic tumors, but familial cases are now increasingly identified. As opposed to multiple endocrine neoplasia type 1 and Carney complex, in familial isolated pituitary adenoma (FIPA) syndrome no other disease is associated with the familial occurrence of pituitary adenomas. It is an autosomal dominant disease with incomplete variable penetrance. Approximately 20% of patients with FIPA harbour germline mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene located on 11q13. Patients with AIP mutations have an overwhelming predominance of somatotroph and lactotroph adenomas, which often present in childhood or young adulthood. AIP, originally identified as a molecular co-chaperone of several nuclear receptors, is thought to act as a tumor suppressor gene; overexpression of wild-type, but not mutant AIP, reduces cell proliferation while knockdown of AIP stimulates it. AIP is shown to bind various proteins, including the aryl hydrocarbon receptor, Hsp90, phosphodiesterases, survivin, RET and the glucocorticoid receptor, but currently it is not clear which interaction has the leading role in pituitary tumorigenesis. This chapter summarizes the available clinical and molecular data regarding the role of AIP in the pituitary gland.

The role of the aryl hydrocarbon receptor-interacting protein gene in familial and sporadic pituitary adenomas

CONTEXT

Mutations have been identified in the aryl hydrocarbon receptor-interacting protein (AIP) gene in familial isolated pituitary adenomas (FIPA). It is not clear, however, how this molecular chaperone is involved in tumorigenesis.

OBJECTIVE

AIP sequence changes and expression were studied in FIPA and sporadic adenomas. The function of normal and mutated AIP molecules was studied on cell proliferation and protein-protein interaction. Cellular and ultrastructural AIP localization was determined in pituitary cells.

PATIENTS

Twenty-six FIPA kindreds and 85 sporadic pituitary adenoma patients were included in the study.

RESULTS

Nine families harbored AIP mutations. Overexpression of wild-type AIP in TIG3 and HEK293 human fibroblast and GH3 pituitary cell lines dramatically reduced cell proliferation, whereas mutant AIP lost this ability. All the mutations led to a disruption of the protein-protein interaction between AIP and phosphodiesterase-4A5. In normal pituitary, AIP colocalizes exclusively with GH and prolactin, and it is found in association with the secretory vesicle, as shown by double-immunofluorescence and electron microscopy staining. In sporadic pituitary adenomas, however, AIP is expressed in all tumor types. In addition, whereas AIP is expressed in the secretory vesicle in GH-secreting tumors, similar to normal GH-secreting cells, in lactotroph, corticotroph, and nonfunctioning adenomas, it is localized to the cytoplasm and not in the secretory vesicles.

CONCLUSIONS

Our functional evaluation of AIP mutations is consistent with a tumor-suppressor role for AIP and its involvement in familial acromegaly. The abnormal expression and subcellular localization of AIP in sporadic pituitary adenomas indicate deranged regulation of this protein during tumorigenesis.

Silent familial isolated pituitary adenomas: histopathological and clinical case report

Familial isolated pituitary adenoma (FIPA) is a rare condition independent of Carney Complex or MEN1. An international multicenter study recently described 28 nonfunctioning pituitary adenomas in 26 families with only two homogeneous nonsecreting phenotype families consistent of silent GH and silent gonadotroph adenomas, respectively. We present the clinical, genetic, and morphological analysis of two silent pituitary adenomas occurring in a man and his daughter, and discuss the differential diagnosis associated with their histological, immunohistochemical, and ultrastructural features. The patients developed invasive nonsecreting macroadenomas manifesting only with compressive symptoms. Genetic analysis in the father showed no MEN-1 germ-line mutation. Tissue samples obtained after paraseptal trans-sphenoidal surgery were studied by immunohistochemistry for adenohypophyseal hormones, low molecular weight cytokeratins (CAM 5.2), proliferation markers, and anterior pituitary transcription factors (Pit-1 and SF-1) and by electron microscopy for secretory granules. The clinical, histological, and immunohistochemical features of the lesions posed a differential diagnosis between a null cell adenoma and a silent corticotroph adenoma (Type II); on the basis of immunohistochemical stains for cytokeratin and adenohypophysis cell lineage markers, tumor behavior and ultrastructural studies we concluded for the second. The reported cases represent an as yet undescribed example of homogeneous family with silent corticotroph adenomas (Type II). Our observations support the trend for more aggressive behavior in nonsecreting FIPAs as compared with sporadic adenomas.

Pituitary adenoma predisposition caused by germline mutations in the AIP gene

Pituitary adenomas are common in the general population, and understanding their molecular basis is of great interest. Combining chip-based technologies with genealogy data, we identified germline mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene in individuals with pituitary adenoma predisposition (PAP). AIP acts in cytoplasmic retention of the latent form of the aryl hydrocarbon receptor and also has other functions. In a population-based series from Northern Finland, two AIP mutations account for 16% of all patients diagnosed with pituitary adenomas secreting growth hormone and for 40% of the subset of patients who were diagnosed when they were younger than 35 years of age. Typically, PAP patients do not display a strong family history of pituitary adenoma; thus, AIP is an example of a low-penetrance tumor susceptibility gene.

Familial acromegaly: a familial report and review of the literature

Familial acromegaly without features of multiple endocrine neoplasie type 1 (MEN 1) is an exceptional clinical entity. We report in this article three cases of acromegaly due to pituitary macroadenomas without any other endocrinopathy in a family. A 31-year-old woman (subject A) and her 34-year-old sister (subject B) with elevated basal rolactin (PRL) levels, elevated growth hormone (GH) levels during the oral glucose tolerance test (OGTT) and a pituitary adenoma in Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) were diagnosed as acromegaly. Subject A was treated only with radiotherapy and Lysuride. Subject B underwent transsphenoidal microsurgical extirpation 15 years ago. 11 years later her 24-year-old son (subject C) also presented with typical signs of acromegaly, elevated basal PRL level and elevated GH levels during OGTT. A pituitary macroadenoma was identified by MRI and he also underwent transsphenoidal adenomectomy. Pathology reports confirmed the diagnosis of GH-secreting pituitary adenoma in subject B and C. Immunocytochemistry revealed that tumours of subject B (> 20% of tumour cells) and C (> 50% of tumour cells) were positive for GH. Tumours of subject B (> 10% of tumour cells) and C (> 50% of tumour cells) also exhibited immunoreactivity for PRL. On investigation of histocompatibility antigens, it was observed that the subject A, B, and C shared the same haplotypes [HLA A24(9), HLA B13(6), HLA B35, HLA DQ7(3), HLA DR13(6)] and so it is very possible that investigation of HLA antigens in patients with pituitary tumour, contributes to better identification of its familial nature and frequency. Here we describe an acromegaly family and the distributions of HLA antigens.

Isolated familial somatotropinoma

The great majority of growth hormone (GH)-secreting pituitary tumors are sporadic, though a few occur with a familial aggregation, either as a component of multiple endocrine neoplasia, type 1 (MEN1) or Carney Complex, or when unassociated with other tumors, as isolated familial somatotropinomas (IFS). This report reviews the clinical and genetic information available from the 46 families reported to date with the latter syndrome. In contrast to sporadic tumors, GH-secreting tumors in IFS occur at an earlier age, especially when all affected family members are from a single generation. The IFS gene is believed to be a tumor suppressor gene, based on the presence of loss of heterozygosity. Although the gene still remains to be identified there is strong evidence for linkage to a locus of less than 10 Mb on chromosome 11q13.1-13.3.

A kindred of familial acromegaly without evidence for linkage to MEN-1 locus

Familial acromegaly (FA) is a rare inherited disease characterized by clustering of somatotrophic adenomas and acromegaly within a family without other manifestations of multiple endocrine neoplasia-type 1 (MEN-1). The genetic basis of this pituitary-specific phenotype is largely unknown, and its relationship to the MEN-1 locus on chromosome 11q13 also remains unclear. To test the hypothesis that FA results from a germline mutation of the MEN-1 locus, we performed a linkage analysis in a Japanese family with 2 members showing manifestations of acromegaly due to somatotroph adenomas. We also examined the adenoma of one patient for loss of heterozygosity (LOH) at 11q13 locus and for the presence of mutations of codon 201 and 227 in the gene for Gsalpha. Our results provided no evidence that either germline alterations of the MEN-1 locus, LOH at 11q13, or somatic mutation of Gsalpha plays a causative role in the development of somatotroph adenomas in our FA family. Together with the previous reports, these results suggest that there are at least two distinct subgroups of FA: one that results from a mutation in MEN-1 locus and the other whose causative gene is located outside the 11q13 locus.

Isolated familial somatotropinomas: clinical features and analysis of the MEN1 gene

Isolated familial somatotropinomas (IFS) rarely occurs in the absence of multiple endocrine neoplasia type I (MEN1) or the Carney complex. In the present study we report two Italian siblings affected by GH-secreting adenomas. There was no history of parental consanguinity. The sister presented at 18 years of age with secondary amenorrhea and acromegalic features and one of her two brothers presented with gigantism at the same age. Endocrinological investigations confirmed GH hypersecretion in both cases. Although a pituitary microadenoma was detected in both patients, transsphenoidal surgery was not successful. The sister received conventional radiotherapy and acromegaly is now considered controlled; the brother is being treated with octreotide LAR 30 mg monthly and the disease is considered clinically active. Patients, their parents and the unaffected brother underwent extensive evaluation, and no features of MEN1 or Carney complex were found. Analysis of polymorphic microsatellite markers from chromosome 11q13 (D11S599, D11S4945, D11S4939, D11S4938 and D11S987) showed that the acromegalic siblings had inherited different maternal chromosomes and shared the paternal chromosome. No pathogenic MEN1 sequence changes were detected by sequencing or dideoxy fingerprinting of the coding sequence (exons 2-10) and exon/intron junctions. Although mutations in the promoter, introns or untranslated regions of the MEN1 gene cannot be excluded, germline mutations within the coding region of this gene do not appear responsible for IFS in this family.

Multiple endocrine neoplasia type 1

The recent cloning of the gene responsible for multiple endocrine neoplasia type 1 (MEN 1) has opened new avenues for both clinical and basic science research in the field of endocrine oncology. A large amount of genetic information, particularly those in relation to germline and somatic mutations, has since been published during the last 2 years. This new knowledge has provided important insights into its gene function. The significance of these advances in relation to clinical management and future directions for research is discussed.

Sporadic pituitary tumours: from epidemiology to use of databases

Pituitary tumours account for 10% of intracranial neoplasms and have an annual incidence of about 25 per million head of population. Prolactinomas and non-functioning tumours are the most common subtypes clinically, as well as in surgical and histopathological series. In pre-pubertal children, corticotrophinomas, although rare, are the most common subtype, prolactinomas being most common in adolescents. In autopsy series, 11% of pituitaries harbour an adenoma. These are usually small (less than 10 mm in diameter), and where examined, about half are prolactinomas. Computed tomography or magnetic resonance imaging examination of normal subjects reveals abnormalities of greater than 3 mm in diameter in 10% of pituitaries. Other cancers in patients with pituitary tumours are confined to acromegalics, in whom colonic lesions are more prevalent than in the general population. Several long-term sequelae of pituitary tumours with respect to morbidity and mortality have been identified from retrospective analyses. However, data on these are not standardized, requiring the development of national databases and registers to collect clinical outcomes from large cohorts according to agreed standard proformas. These registers will provide a sufficient number of cases for statistically valid conclusions on different clinical subgroups. The development of national guidelines for best practice for the management of patients with these tumours provides the basis for an audit of the management process and outcomes between centres. This will inform decisions on the optimum configuration of services for such patients.

Molecular pathogenesis of acromegaly

Acromegaly is generally caused by growth hormone (GH) hypersecretion from a benign, monoclonal pituitary adenoma. As in other neoplastic conditions, pituitary tumor formation and dysregulated hormone secretion are most likely the ultimate result of a series of genetic alterations. A number of molecular and biochemical defects have been associated with pituitary tumorigenesis. Molecular events such as tumor suppressor gene inactivation and oncogene activation involved in pituitary tumor progression are examined. The role of hypothalamic regulatory hormones and hereditary syndromes involving acromegaly are also discussed.

Familial acromegaly: case report and review of the literature

Familial acromegaly is an exceptional clinical entity when not associated with features of multiple endocrine neoplasia type 1 (MEN1). We report here 3 pedigrees in each of which 2 patients have been shown to develop acromegaly. In 4 patients, clinical follow-up, and biological screening allowed to confidently exclude MEN1. Absence of mutation in the MEN1 gene after direct DNA analysis in 2 pedigrees reinforces the conviction that the families do not have MEN1. In families 1 and 2, diagnosis was made at a very early age and voluminous adenomas with suprasellar expansion were already present at the time of diagnosis. We review the 20 previous reports of familial acromegaly, some of them questionable. Our 3 families, combined with some other published pedigrees, allow the delineation of a familial form of acromegaly, distinct from MEN1. Dominant inheritance with reduced, age-dependant penetrance is the most parsimonious model to explain the recurrences. Gs protein pathway could be the site of action of the gene responsible of familial acromegaly, but no data have been published to sustain or reject this hypothesis.

Pathogenesis of pituitary tumors

This article focuses on the molecular events associated with pituitary tumorigenesis. An accurate description of the molecular pathogenesis of pituitary adenomas will have an important impact on clinical practice: identification of specific molecular markers of tumor invasiveness and recurrence will allow earlier therapeutic intervention and selection of appropriate follow-up protocols; family screening may become practically feasible; and potent subcellular therapies may be developed for patients with nonfunctioning tumors, in whom nonsurgical therapies are ineffective, and for those with resistant hormone-secreting tumors.

Absence of germ-line mutations of the multiple endocrine neoplasia type 1 (MEN1) gene in familial pituitary adenoma in contrast to MEN1 in Japanese

Germ-line mutations of the MEN1 gene were analyzed in five cases of familial and four cases of sporadic multiple endocrine neoplasia type 1 (MEN-1), six cases in three independent pedigrees of familial pituitary adenoma without MEN-1, and three cases of familial isolated primary hyperparathyroidism (FIHP) in Japanese. Eight different types of germ-line mutations in all nine cases of MEN-1 were distributed in exons 2, 3, 7, and 10 and intron 7 of the MEN1 gene. Loss of heterozygosity (LOH) on 11q13 was detected in all nine tumors of these cases with microsatellite analysis. No germ-line mutation of the MEN1 gene was detected in three pedigrees of familial pituitary adenoma and three cases of FIHP. LOH on 11q13 was detected in two cases in one pedigree of familial pituitary adenoma, and one of them showed a heterozygous somatic mutation of the MEN1 gene. No LOH on 11q13 was detected in three cases of FIHP. Based on these, we conclude that the loss of function of menin is etiological for familial or sporadic MEN-1, but not for FIHP or most familial pituitary adenoma without MEN-1.