Genome-wide scan identifies novel modifier loci of acromegalic phenotypes for isolated familial somatotropinoma

Update on the Genetics of Pituitary Tumors

Pituitary adenomas are common intracranial neoplasms, with diverse phenotypes. Most of these tumors occur sporadically and are not part of genetic disorders. Over the last decades numerous genetic studies have led to identification of somatic and germline mutations associated with pituitary tumors, which has advanced the understanding of pituitary tumorigenesis. Exploring the genetic background of pituitary neuroendocrine tumors can lead to early diagnosis associated with better outcomes, and their molecular mechanisms should lead to novel targeted therapies even for sporadic tumors. This article summarizes the genes and the syndromes associated with pituitary tumors.

FGFR2 gene polymorphism rs2981582 is associated with non-functioning pituitary adenomas in Chinese Han population: a case-control study

The association of the fibroblast growth factor receptor 2 gene (FGFR2) polymorphism rs2981582 with breast cancer has been extensively studied, whereas the role of this polymorphism in non-functioning pituitary adenoma (NFPA) has not been elucidated. We thus investigated a potential association of rs2981582 with NFPA. A total of 79 patients and 142 healthy control participants were enrolled in our study. DNA of the participants was extracted from peripheral blood samples and genotyped by using the MassARRAY method. We found that the AA genotype was associated with a higher risk of developing NFPA (OR = 1.743, 95%CI: 1.151–2.64, P=0.008). After adjusting for risk factors, significant difference was still observed between the two groups (OR = 1.862, 95%CI: 1.172–2.957, P=0.008). Moreover, under the assumptions of the recessive model (OR = 3.051, 95%CI: 1.403–6.635, P=0.005) and the additive model (AG: OR = 0.329, 95%CI: 0.144–0.755, P=0.009; AA: OR = 0.326, 95%CI: 0.141–0.757, P=0.009), rs2981582 was associated with an increased risk of NFPA. Our results proved that FGFR2 rs2981582 AA genotype was associated with a higher risk of NFPA. The recessive model and additive model also showed increased the risk of NFPA.

Genetic Aspects of Pituitary Adenomas

Although most of pituitary adenomas are benign, they may cause significant burden to patients. Sporadic adenomas represent the vast majority of the cases, where recognized somatic mutations (eg, GNAS or USP8), as well as altered gene-expression profile often affecting cell cycle proteins have been identified. More rarely, germline mutations predisposing to pituitary adenomas -as part of a syndrome (eg, MEN1 or Carney complex), or isolated to the pituitary (AIP or GPR101) can be identified. These alterations influence the biological behavior, clinical presentations and therapeutic responses, and their full understanding helps to provide appropriate care for these patients.

MEN1, MEN4, and Carney Complex: Pathology and Molecular Genetics

Pituitary adenomas are a common feature of a subset of endocrine neoplasia syndromes, which have otherwise highly variable disease manifestations. We provide here a review of the clinical features and human molecular genetics of multiple endocrine neoplasia (MEN) type 1 and 4 (MEN1 and MEN4, respectively) and Carney complex (CNC). MEN1, MEN4, and CNC are hereditary autosomal dominant syndromes that can present with pituitary adenomas. MEN1 is caused by inactivating mutations in the MEN1 gene, whose product menin is involved in multiple intracellular pathways contributing to transcriptional control and cell proliferation. MEN1 clinical features include primary hyperparathyroidism, pancreatic neuroendocrine tumours and prolactinomas as well as other pituitary adenomas. A subset of patients with pituitary adenomas and other MEN1 features have mutations in the CDKN1B gene; their disease has been called MEN4. Inactivating mutations in the type 1α regulatory subunit of protein kinase A (PKA; the PRKAR1A gene), that lead to dysregulation and activation of the PKA pathway, are the main genetic cause of CNC, which is clinically characterised by primary pigmented nodular adrenocortical disease, spotty skin pigmentation (lentigines), cardiac and other myxomas and acromegaly due to somatotropinomas or somatotrope hyperplasia.

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.

Clinical experience in the screening and management of a large kindred with familial isolated pituitary adenoma due to an aryl hydrocarbon receptor interacting protein (AIP) mutation

CONTEXT

Germline AIP mutations usually cause young-onset acromegaly with low penetrance in a subset of familial isolated pituitary adenoma families. We describe our experience with a large family with R304* AIP mutation and discuss some of the diagnostic dilemmas and management issues.

OBJECTIVE

The aim of the study was to identify and screen mutation carriers in the family.

PATIENTS

Forty-three family members participated in the study.

SETTING

The study was performed in university hospitals.

OUTCOME

We conducted genetic and endocrine screening of family members.

RESULTS

We identified 18 carriers of the R304* mutation, three family members with an AIP-variant A299V, and two family members who harbored both changes. One of the two index cases presented with gigantism and pituitary apoplexy, the other presented with young-onset acromegaly, and both had surgery and radiotherapy. After genetic and clinical screening of the family, two R304* carriers were diagnosed with acromegaly. They underwent transsphenoidal surgery after a short period of somatostatin analog treatment. One of these two patients is in remission; the other achieved successful pregnancy despite suboptimal control of acromegaly. One of the A299V carrier family members was previously diagnosed with a microprolactinoma; we consider this case to be a phenocopy. Height of the unaffected R304* carrier family members is not different compared to noncarrier relatives.

CONCLUSIONS

Families with AIP mutations present particular problems such as the occurrence of large invasive tumors, poor response to medical treatment, difficulties with fertility and management of pregnancy, and the finding of AIP sequence variants of unknown significance. Because disease mostly develops at a younger age and penetrance is low, the timing and duration of the follow-up of carriers without overt disease requires further study. The psychological and financial impact of prolonged clinical screening must be considered. Excellent relationships between the family, endocrinologists, and geneticists are essential, and ideally these families should be managed in centers with specialist expertise.

Screening for AIP gene mutations in a Han Chinese pituitary adenoma cohort followed by LOH analysis

OBJECTIVE

The aryl hydrocarbon receptor interacting protein gene (AIP) is associated with pituitary adenoma (PA). AIP has not been sequenced in East Asian PA populations, so we performed this study in a Han Chinese cohort.

DESIGN

Our study included six familial PA pedigrees comprising 16 patients and 27 unaffected relatives, as well as 216 sporadic PA (SPA) patients and 100 unrelated healthy controls.

METHODS

AIP sequencing was carried out on genomic DNA isolated from blood samples. Multiplex ligation-dependent probe amplification and microsatellite marker analyses on DNA from the paired tumor tissues were performed for loss of heterozygosity analysis.

RESULTS

We identified three common and four rare single nucleotide polymorphisms (SNPs), one intron insertion, one novel synonymous variant, four novel missense variants, and a reported nonsense mutation in three familial isolated PA (FIPA) cases from the same family. Large genetic deletions were not observed in the germline but were seen in the sporadic tumor DNA from three missense variant carriers. The prevalence of AIP pathogenic variants in PA patients here was low (3.88%), but was higher in somatotropinoma patients (9.30%), especially in young adults (≤30 years) and pediatric (≥18 years) paients (17.24% and 25.00% respectively). All AIP variant patients suffered from macroadenomas. However, the AIP mutation rate in FIPA families was low in this cohort (16.67%, 1/6 families).

CONCLUSION

AIP gene mutation may not be frequent in FIPA or SPA from the Han Chinese population. AIP sequencing and long-term follow-up investigations should be performed for young patients with large PAs and their families with PA predisposition.

Should aip gene screening be recommended in family members of FIPA patients with R16H variant?

Germline mutations of aryl-hydrocarbon-receptor interacting protein (AIP) are associated with pituitary adenoma predisposition. They occur in 20 % of familial isolated pituitary adenoma (FIPA) and in about 3-5 % of sporadic pituitary adenomas, especially in early onset somatotropinomas and prolactinomas. Our aim was to evaluate the clinical and genetic features of a large Italian FIPA family, where an AIP variant was identified. AIP direct sequencing from genomic DNA was carried out in 16 available family members. AIP R16H carriers also underwent magnetic resonance imaging and hormonal assessments. AIP mutations were also searched in 16 patients with sporadic growth hormone-secreting pituitary adenoma and in 6 unrelated patients in whom pituitary adenoma was excluded. We found an AIP R16H variation in two family members harbouring a pituitary adenoma and in 6 unaffected family members. No AIP mutation was found neither in growth hormone-secreting pituitary adenoma patients, nor in the unrelated patients without pituitary adenoma. We report a FIPA family harbouring an AIP R16H change, supporting the hypothesis that the latter represents a variant of unknown significance.

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.

Familial isolated pituitary adenomas: an emerging clinical entity

Familial pituitary tumors are increasingly recognized. While some of these cases are related to wellknown syndromic conditions such as multiple endocrine neoplasia type 1 (MEN1) or Carney complex, others belong to the familial isolated pituitary adenoma (FIPA) patient group. The discovery of heterozygous, loss-of-function germline mutations in the gene encoding the aryl hydrocarbon receptor interacting protein (AIP) in 2006 has subsequently enabled the identification of a mutation in this gene in 20% of FIPA families and 20% of childhood-onset simplex soma- totroph adenomas. The exact mechanism by which the lack of AIP leads to pituitary adenomas is not clear. AIP mutations cause a low penetrance autosomal dominant disease with often a distinct phenotype characterized by young-onset, aggressive, large GH, mixed GH and PRL or PRL-secreting adenomas. This review aims to summarize currently available clinical data on AIP mutation-positive and negative FIPA patients.

Familial isolated pituitary adenomas: from genetics to therapy

According to autopsy and radiological data, pituitary adenomas (PAs) develop in approximately 15% to 20% of the population. The great majority of PAs arise sporadically and affect adults. Rarely they are diagnosed in children and adolescents. Approximately 5% of cases are thought to be familial. Inherited conditions associated with pituitary tumors include multiple endocrine neoplasia type 1 (MEN-1) and type 4 (MEN-4), (CNC) Carney Complex, and familial isolated PA (FIPA) syndrome. FIPA is an autosomal dominant condition, defined by the presence of two or more patients affected by PAs in the same kindred, and no other associated condition. Germline mutations of the aryl hydrocarbon receptor interacting protein gene located on chromosome 11q13 have been reported in 15%-40% of FIPA cases. In the remaining cases, genetic defect are unidentified. This article focuses on FIPA clinical, pathological, genetic features, and therapeutic management.

Genetic susceptibility in pituitary adenomas: from pathogenesis to clinical implications

Pituitary adenomas usually present sporadically, with a multifactorial pathogenesis including somatic mutational events in cancer-related genes. Genetic predisposition implies the presence of germline DNA alterations with a range of impacts on pituitary cell biology, translating into a variable penetrance of the disease. Genetic causes must be considered in the presence of specific clinical settings, such as familial occurrence of pituitary adenoma, with or without extrapituitary diseases, and may also be suspected in young patients (<30 years of age) with macroadenomas. We review the clinical implications of genetic predisposition, with special attention on multiple endocrine neoplasia type 1, Carney complex and familial isolated pituitary adenoma. Genetic screening in selected patients with an apparently sporadic disease is also discussed.

The R304X mutation of the aryl hydrocarbon receptor interacting protein gene in familial isolated pituitary adenomas: Mutational hot-spot or founder effect?

BACKGROUND

Mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene have been described in about 15% of kindreds with familial isolated pituitary adenomas and in a minority of early onset sporadic pituitary adenomas (PA). Among the AIP mutations reported so far, the R304X (AIPR304X) represents, together with the "Finnish mutation" Q14X, the most common one.

METHODS

Three AIPR304X Italian families, including a newly reported kindred, have been genotyped for 12 genetic markers surrounding the AIP gene in order to look for a potential founder effect in Italy. Disease penetrance and genotype-phenotype correlations were also addressed.

RESULTS

Analysis of chromosome 11' genetic markers revealed a common haplotype in 2 AIPR304X kindreds originating from central Italy. Overall, 17 mutations carriers were identified, including 7 patients and 10 unaffected subjects, respectively, arguing in this case for a disease penetrance of 41%. Mean age at diagnosis was 19.1±6.7 yr old, with females tending to be older than males. Though most PA were somatotropinomas (6/7), a great variability in disease severity was observed, even between subjects sharing the same at-risk haplotype.

CONCLUSION

These data provide strong evidence for a new founder effect of the AIPR304X mutation in central Italy and the observed variations in disease severity point out the role of additional genetic or environmental factors in such kindreds.

Aggressive prolactinoma in a child related to germline mutation in the ARYL hydrocarbon receptor interacting protein (AIP) gene

The objective of this study was to describe a familial screening for AIP mutations in the context of aggressive prolactinoma in childhood. A 12-year-old boy, presented headaches and bilateral hemianopsia. He had adequate height and weight for his age (50th percentile), Tanner stage G1 P1. His bone age was 10 years. Prolactin was 10.560 ng/mL (3-25), FSH and LH were undetectable, IGF-1, TSH, Free T4, ACTH, and cortisol were within normal ranges. MRI showed a pituitary macroadenoma, 5.3 X 4.0 X 3.5 cm with compression of the optic chiasm, bilateral cavernous sinus invasion, encasement of carotids, and extension to clivus. Surgical debulking was performed. Resistance to cabergoline was characterized and he was submitted to two surgeries and radiotherapy. Immunohistochemical evaluation included prolactin, ACTH, GH, FSH, LH,AIP, c-erb B2, Ki-67, and p53. Genomic DNA was isolated from the index case and 48 relatives, PCR and sequencing were performed.A germline A195V mutation in AIP was identified in the index case and in five asymptomatic relatives. Germline mutations in the AIP gene may be involved in the predisposition to pituitary adenoma formation, as cause or co-factor in pathogenesis of aggressive tumors in young patients.

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.

Clinical, genetic and molecular characterization of patients with familial isolated pituitary adenomas (FIPA)

Familial pituitary adenomas can occur in MEN1 and Carney complex, as well as in the recently characterized familial isolated pituitary adenoma (FIPA) syndrome. FIPA is an autosomal dominant disease with incomplete penetrance, characterized by early-onset disease, often aggressive tumor growth and a predominance of somatotroph and lactotroph adenomas. In 20% of FIPA families, heterozygous mutations have been described in the aryl hydrocarbon receptor interacting (AIP) gene, whereas in other families the causative gene(s) are unknown. It has been suggested that AIP is a tumor suppressor gene and although experimental data support this hypothesis, the exact molecular mechanism by which its disruption leads to tumorigenesis is unclear. Here we discuss the clinical, genetic and molecular features of patients with 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.