Prevalence of AIP mutations in a series of Turkish acromegalic patients: are synonymous AIP mutations relevant?

Low frequency of AIP mutations in patients with young-onset sporadic pituitary macroadenomas

PURPOSE

Mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene cause familial isolated pituitary adenomas (FIPA). AIP mutations have also been found in patients with apparently sporadic pituitary adenomas, particularly in young patients with large adenomas. The aim of this study was to determine the frequency of AIP germline mutations in patients with young-onset sporadic pituitary macroadenomas.

METHODS

The AIP gene was sequenced in 218 Portuguese patients with sporadic pituitary macroadenomas diagnosed before the age of 40 years.

RESULTS

Heterozygous rare sequence variants in AIP were identified in 18 (8.3%) patients. However, only four (1.8%) patients had pathogenic or likely pathogenic variants. These consisted of two already known mutations (p.Arg81* and p.Leu115Trpfs*41) and two novel mutations (p.Glu246*, p.Ser53Thrfs*36). All four patients had GH-secreting adenomas diagnosed between the ages of 14 and 25 years. The frequency of AIP pathogenic or likely pathogenic variants in patients under the age of 30 and 18 years was 3.4% and 5.0%, respectively.

CONCLUSION

The frequency of AIP mutations in this cohort was lower than in other studies. Previous reports may have overestimated the contribution of AIP mutations due to the inclusion of genetic variants of uncertain significance. The identification of novel AIP mutations expands the known spectrum of genetic causes of pituitary adenomas and may help understand the role of AIP mutations in the molecular mechanisms underlying pituitary tumorigenesis.

A. Phosphodiesterases and cAMP Pathway in Pituitary Diseases

Human phosphodiesterases (PDEs) comprise a complex superfamily of enzymes derived from 24 genes separated into 11 PDE gene families (PDEs 1-11), expressed in different tissues and cells, including heart and brain. The isoforms PDE4, PDE7, and PDE8 are specific for the second messenger cAMP, which is responsible for mediating diverse physiological actions involving different hormones and neurotransmitters. The cAMP pathway plays an important role in the development and function of endocrine tissues while phosphodiesterases are responsible for ensuring the appropriate intensity of the actions of this pathway by hydrolyzing cAMP to its inactive form 5'-AMP. PDE1, PDE2, PDE4, and PDE11A are highly expressed in the pituitary, and overexpression of some PDE4 isoforms have been demonstrated in different pituitary adenoma subtypes. This observed over-expression in pituitary adenomas, although of unknown etiology, has been considered a compensatory response to tumorigenesis. PDE4A4/5 has a unique interaction with the co-chaperone aryl hydrocarbon receptor-interacting protein (AIP), a protein implicated in somatotroph tumorigenesis via germline loss-of-function mutations. Based on the association of low PDE4A4 expression with germline AIP-mutation-positive samples, the available data suggest that lack of AIP hinders the upregulation of PDE4A4 protein seen in sporadic somatotrophinomas. This unique disturbance of the cAMP-PDE pathway observed in the majority of AIP-mutation positive adenomas could contribute to their well-described poor response to somatostatin analogs and may support a role in tumorigenesis.

Clinical Relevance of Genetic Analysis in Patients With Pituitary Adenomas: A Systematic Review

Pituitary adenomas (PA) are amongst the most prevalent intracranial tumors, causing complications by hormonal overproduction or deficiency and tumor mass effects, with 95% of cases occurring sporadically. Associated germline mutations (AIP, MEN1, CDKN1B, PRKAR1A, SDHx) and Xq26.3 microduplications are increasingly identified, but the clinical consequences in sporadic PA remain unclear. This systematic review evaluates predictors of a genetic cause of sporadic PA and the consequences for treatment outcome. We undertook a sensitive MEDLINE/Pubmed, EMBASE, and Web of Science search with critical appraisal of identified studies. Thirty-seven studies on predictors of mutations and 10 studies on the influence on treatment outcome were included. AIP and MEN1 mutations were associated with young age of PA diagnosis. AIP mutations were also associated with gigantism and macroadenomas at time of diagnosis. Xq26.3 microduplications were associated with PA below the age of five. AIP and MEN1 mutation analysis is therefore recommended in young patients (≤30 years). AIP mutation analysis is specifically recommended for patients with PA induced gigantism and macroadenoma. Screening for Xq26.3 microduplications is advisable in children below the age of five with increased growth velocity due to PA. There is no evidence supporting mutation analysis of other genes in sporadic PA. MEN1 mutation related prolactinoma respond well to dopamine agonists while AIP mutation associated somatotroph and lactotroph adenoma are frequently resistant to medical treatment. In patients harboring an Xq26.3 microduplication treatment is challenging, although outcome is not different from other patients with PA induced gigantism. Effective use of genetic analysis may lead to early disease identification, while knowledge of the impact of germline mutations on susceptibility to various treatment modalities helps to determine therapeutic strategies, possibly lowering disease morbidity.

Screening of AIP Gene Variations in a Cohort of Turkish Patients with Young-Onset Sporadic Hormone-Secreting Pituitary Adenomas

Aims: Aryl hydrocarbon receptor-interacting protein (AIP) gene mutations have long been associated with apparently sporadic pituitary adenomas (PAs) with a prevalence range of 0-12%. The aim of this study was to evaluate the frequency of germline AIP variations in a large cohort of apparently sporadic PAs diagnosed before the age of 40 years, who did not exhibit hypercalcemia and/or MEN1 syndrome components during long-term follow-up. Materials and Methods: A total of 97 patients, diagnosed with functional PAs ≤40 years old, composed of somatotropinoma (n = 55), prolactinoma (n = 25), and corticotrophinoma (n = 17), were recruited for this study. Fifty-one of these patients [somatotropinoma (n = 30), prolactinoma (n = 15), and corticotrophinoma (n = 11)] were previously reported as AIP mutation-negative by Sanger sequencing. The entire coding sequence of the AIP gene, along with exon/intron boundaries and the untranslated regions of 41 newly recruited patients, were sequenced for germline variations. In addition, all patients were subjected to multiplex ligation-dependent probe amplification to detect copy number variations in the AIP gene. Results: The AIP c.911G>A: p.Arg304Gln (rs104894190) variant was detected in only two patients with functional PA: one with somatotropinoma [in 1/55 (1.8%)] and one with prolactinoma [in 1/25 (4%)]. None of the corticotrophinomas revealed AIP gene alterations. Thus, the overall prevalence of AIP variation was 2.1% in our cohort. Conclusions: Germline AIP gene variations among Turkish patients with apparently sporadic PAs are relatively rare among patients ≤40 years old. None of the patients in our cohort revealed any obviously pathogenic AIP variants.

Germline mutations of aryl hydrocarbon receptor-interacting protein (AIP) gene and somatostatin receptor 1-5 and AIP immunostaining in patients with sporadic acromegaly with poor versus good response to somatostatin analogues

OBJECTIVE

To determine aryl hydrocarbon interacting protein (AIP) gene variations and AIP and somatostatin receptor (SSTR) 1-5 immunostaining in patients with apparently sporadic acromegaly with poor versus good response to somatostatin analogues (SRLs).

METHODS

A total of 94 patients (66 with poor and 28 with good response to SRLs) were screened for the AIP gene variations using Sanger sequencing. Immunostaining was performed in 60 tumors.

RESULTS

Several variations, albeit some with undetermined significance, were detected, especially in poor responder patients. The prevalence of AIP mutation was 2.1% in the whole group and 1.5% in patients with poor response to SRLs. AIP, SSTR2A, and SSTR2B immunostainings were decreased in patients with poor response (p < 0.05 for all), and other SSTRs did not differ between the groups (p > 0.05 for all). Patients with low AIP had decreased levels of SSTR2A and SSTR3 (p < 0.05 for all). AIP and SSTR2A immunostainings were positively correlated to the treatment response and age at diagnosis was negatively correlated (p < 0.05 for all). In poor responder patients with high SSTR2A immunostaining, SSTR2B immunostaining and preoperative tumor size were positively and negatively correlated, respectively, to SRL response (p < 0.05 for all).

CONCLUSIONS

Lack of response to SRLs does not necessarily increase the risk of harboring AIP mutations. The finding of decreased AIP, SSTR2A, and SSTR2B immunostaining in patients with poor response to SRLs and decreased SSTR2A and SSTR3 level in those with low AIP immunostaining suggests a possible interaction between AIP and some SSTR subtypes that might alter SRL sensitivity.

Feline hypersomatotropism and acromegaly tumorigenesis: a potential role for the AIP gene

Acromegaly in humans is usually sporadic, however up to 20% of familial isolated pituitary adenomas are caused by germline sequence variants of the aryl-hydrocarbon-receptor interacting protein (AIP) gene. Feline acromegaly has similarities to human acromegalic families with AIP mutations. The aim of this study was to sequence the feline AIP gene, identify sequence variants and compare the AIP gene sequence between feline acromegalic and control cats, and in acromegalic siblings. The feline AIP gene was amplified through PCR using whole blood genomic DNA from 10 acromegalic and 10 control cats, and 3 sibling pairs affected by acromegaly. PCR products were sequenced and compared with the published predicted feline AIP gene. A single nonsynonymous SNP was identified in exon 1 (AIP:c.9T > G) of two acromegalic cats and none of the control cats, as well as both members of one sibling pair. The region of this SNP is considered essential for the interaction of the AIP protein with its receptor. This sequence variant has not previously been reported in humans. Two additional synonymous sequence variants were identified (AIP:c.481C > T and AIP:c.826C > T). This is the first molecular study to investigate a potential genetic cause of feline acromegaly and identified a nonsynonymous AIP single nucleotide polymorphism in 20% of the acromegalic cat population evaluated, as well as in one of the sibling pairs evaluated.

Sporadic pituitary adenomas: the role of germline mutations and recommendations for genetic screening

Although most pituitary adenomas occur sporadically, these common tumors can present in a familial setting in approximately 5% of cases. Germline mutations in several genes with autosomal dominant (AIP, MEN1, CDKN1B, PRKAR1A, SDHx) or X-linked dominant (GPR101) inheritance are causative of familial pituitary adenomas. Due to variable disease penetrance and occurrence of de novo mutations, some patients harboring germline mutations have no family history of pituitary adenomas (simplex cases). Areas covered: We summarize the recent findings on the role of germline mutations associated with familial pituitary adenomas in patients with sporadic clinical presentation. Expert commentary: Up to 12% of patients with young onset pituitary adenomas (age at diagnosis/onset ≤30 years) and up to 25% of simplex patients with gigantism carry mutations in the AIP gene, while most cases of X-linked acrogigantism (XLAG) due to GPR101 duplication are simplex female patients with very early disease onset (<5 years). With regard to the syndromes of multiple endocrine neoplasia (MEN), MEN1 mutations can be identified in a significant proportion of patients with childhood onset prolactinomas. Somatotroph and lactotroph adenomas are the most common pituitary adenomas associated with germline predisposing mutations. Genetic screening should be considered in patients with young onset pituitary adenomas.

AIP mutations in young patients with acromegaly and the Tampico Giant: the Mexican experience

Although aryl hydrocarbon receptor-interacting protein (AIP) mutations are rare in sporadic acromegaly, their prevalence among young patients is nonnegligible. The objectives of this study were to evaluate the frequency of AIP mutations in a cohort of Mexican patients with acromegaly with disease onset before the age of 30 and to search for molecular abnormalities in the AIP gene in teeth obtained from the "Tampico Giant". Peripheral blood DNA from 71 patients with acromegaly (51 females) with disease onset <30 years was analysed (median age of disease onset of 23 years) and correlated with clinical, biochemical and imaging characteristics. Sequencing was also carried out in DNA extracted from teeth of the Tampico Giant. Five patients (7 %) harboured heterozygous, germline mutations of the AIP gene. In two of them (a 9-year-old girl with gigantism and a young man with symptoms of GH excess since age 14) the c.910C>T (p.Arg304Ter), well-known truncating mutation was identified; in one of these two cases and her identical twin sister, the mutation proved to be a de novo event, since neither of their parents were found to be carriers. In the remaining three patients, new mutations were identified: a frameshift mutation (c.976_977insC, p.Gly326AfsTer), an in-frame deletion (c.872_877del, p.Val291_Leu292del) and a nonsense mutation (c.868A > T, p.Lys290Ter), which are predicted to be pathogenic based on in silico analysis. Patients with AIP mutations tended to have an earlier onset of acromegaly and harboured larger and more invasive tumours. A previously described genetic variant of unknown significance (c.869C > T, p.Ala299Val) was identified in DNA from the Tampico Giant. The prevalence of AIP mutations in young Mexican patients with acromegaly is similar to that of European cohorts. Our results support the need for genetic evaluation of patients with early onset acromegaly.