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

Tall stature and gigantism in adult patients with acromegaly

OBJECTIVES

Increased height in patients with acromegaly could be a manifestation of growth hormone (GH) excess before epiphysis closure. The aim of this study was to evaluate the relationship between the height of adult patients with GH excess related to mid-parental height (MPH) and population mean and to find whether taller patients with acromegaly come from tall families.

METHODS

This is a single-centre, observational study involving 135 consecutive patients with acromegaly diagnosed as adults and no family history of GH excess. We established three categories for height for patients with acromegaly: normal stature, tall stature (TS, height above the 97th percentile (1.88 standard deviations (SD)) to <3 SD for gender- and country-specific data or as a height which was greater than 1.5 SD but less than 2 SD above the MPH) and gigantism (height which was greater than 3 SD) above the gender- and country-specific mean or greater than 2 SD above MPH).

RESULTS

Thirteen percent (17/135) of patients (53% females) met the criteria for gigantism, 10% (14/135) fulfilled the criteria for TS (57% females). Parents and adult siblings were not taller than the population mean.

CONCLUSION

In a group of 135 consecutive adult patients with acromegaly, 23% had increased height based on country-specific and MPH data: 13% presented with gigantism while 10% had TS. The frequency of gigantism and TS in patients diagnosed with GH excess as adults is not higher in males than in females. Patients with acromegaly come from normal-stature families.

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.

Novel AIP mutation in exon 6 causing acromegaly in a German family

The most frequent genetic alteration of familial isolated growth hormone producing pituitary neuroendocrine tumors is a germline mutation of the aryl hydrocarbon receptor-interacting protein (AIP) gene. Various AIP mutations are already known; however, an AIP mutation in exon 6 (c.811_812del; p.Arg271Glyfs*16) has not been reported yet. Here, we report a German family with two identical twins who were both affected by acromegaly and carried the above-mentioned novel AIP mutation. The father was found to be an unaffected carrier, while the paternal aunt most likely suffered from acromegaly as well and died from metastatic colorectal cancer. Apart from reporting a novel AIP mutation, this study does not only highlight the different clinical and histological features of the AIP mutated growth hormone producing pituitary neuroendocrine tumors but also confirms the poor responsiveness of dopamine agonists in AIP mutated acromegaly. Furthermore, it highlights the increased mortality risk of comorbidities typically associated with acromegaly.

Novel Insights into Pituitary Tumorigenesis: Genetic and Epigenetic Mechanisms

Substantial advances have been made recently in the pathobiology of pituitary tumors. Similar to many other endocrine tumors, over the last few years we have recognized the role of germline and somatic mutations in a number of syndromic or nonsyndromic conditions with pituitary tumor predisposition. These include the identification of novel germline variants in patients with familial or simplex pituitary tumors and establishment of novel somatic variants identified through next generation sequencing. Advanced techniques have allowed the exploration of epigenetic mechanisms mediated through DNA methylation, histone modifications and noncoding RNAs, such as microRNA, long noncoding RNAs and circular RNAs. These mechanisms can influence tumor formation, growth, and invasion. While genetic and epigenetic mechanisms often disrupt similar pathways, such as cell cycle regulation, in pituitary tumors there is little overlap between genes altered by germline, somatic, and epigenetic mechanisms. The interplay between these complex mechanisms driving tumorigenesis are best studied in the emerging multiomics studies. Here, we summarize insights from the recent developments in the regulation of pituitary tumorigenesis.

Growth Hormone and Aging: Updated Review

Role of growth hormone (GH) in mammalian aging is actively explored in clinical, epidemiological, and experimental studies. The age-related decline in GH levels is variously interpreted as a symptom of neuroendocrine aging, as one of causes of altered body composition and other unwelcome symptoms of aging, or as a mechanism of natural protection from cancer and other chronic diseases. Absence of GH signals due to mutations affecting anterior pituitary development, GH secretion, or GH receptors produces an impressive extension of longevity in laboratory mice. Extension of healthspan in these animals and analysis of survival curves suggest that in the absence of GH, aging is slowed down or delayed. The corresponding endocrine syndromes in the human have no consistent impact on longevity, but are associated with remarkable protection from age-related disease. Moreover, survival to extremely old age has been associated with reduced somatotropic (GH and insulin-like growth factor-1) signaling in women and men. In both humans and mice, elevation of GH levels into the supranormal (pathological) range is associated with increased disease risks and reduced life expectancy likely representing acceleration of aging. The widely advertised potential of GH as an anti-aging agent attracted much interest. However, results obtained thus far have been disappointing with few documented benefits and many troublesome side effects. Possible utility of GH in the treatment of sarcopenia and frailty remains to be explored.

Emergence of Pituitary Adenoma in a Child during Surveillance: Clinical Challenges and the Family Members' View in an AIP Mutation-Positive Family

INTRODUCTION

Germline aryl hydrocarbon receptor-interacting protein (AIP) mutations are responsible for 15-30% of familial isolated pituitary adenomas (FIPAs). We report a FIPA kindred with a heterozygous deletion in AIP, aiming to highlight the indications and benefits of genetic screening, variability in clinical presentations, and management challenges in this setting.

PATIENTS

An 18-year-old male was diagnosed with a clinically nonfunctioning pituitary adenoma (NFPA). Two years later, his brother was diagnosed with a somatolactotrophinoma, and a small Rathke's cleft cyst and a microadenoma were detected on screening in their 17-year-old sister. Following amenorrhoea, their maternal cousin was diagnosed with hyperprolactinaemia and two distinct pituitary microadenomas. A 12-year-old niece developed headache and her MRI showed a microadenoma, not seen on a pituitary MRI scan 3 years earlier.

DISCUSSION

Out of the 14 members harbouring germline AIP mutations in this kindred, 5 have pituitary adenoma. Affected members had different features and courses of disease. Bulky pituitary and not fully suppressed GH on OGTT can be challenging in the evaluation of females in teenage years. Multiple pituitary adenomas with different secretory profiles may arise in the pituitary of these patients. Small, stable NFPAs can be present in mutation carriers, similar to incidentalomas in the general population. Genetic screening and baseline review, with follow-up of younger subjects, are recommended in AIP mutation-positive families.

AIP mutations in Brazilian patients with sporadic pituitary adenomas: a single-center evaluation

Aryl hydrocarbon receptor-interacting protein (AIP) gene mutations (AIPmut) are the most frequent germline mutations found in apparently sporadic pituitary adenomas (SPA). Our aim was to evaluate the frequency of AIPmut among young Brazilian patients with SPA. We performed an observational cohort study between 2013 and 2016 in a single referral center. AIPmut screening was carried out in 132 SPA patients with macroadenomas diagnosed up to 40 years or in adenomas of any size diagnosed until 18 years of age. Twelve tumor samples were also analyzed. Leukocyte DNA and tumor tissue DNA were sequenced for the entire AIP-coding region for evaluation of mutations. Eleven (8.3%) of the 132 patients had AIPmut, comprising 9/74 (12%) somatotropinomas, 1/38 (2.6%) prolactinoma, 1/10 (10%) corticotropinoma and no non-functioning adenomas. In pediatric patients (≤18 years), AIPmut frequency was 13.3% (2/15). Out of the 5 patients with gigantism, two had AIPmut, both truncating mutations. The Y268* mutation was described in Brazilian patients and the K273Rfs*30 mutation is a novel mutation in our patient. No somatic AIP mutations were found in the 12 tumor samples. A tumor sample from an acromegaly patient harboring the A299V AIPmut showed loss of heterozygosity. In conclusion, AIPmut frequency in SPA Brazilian patients is similar to other populations. Our study identified two mutations exclusively found in Brazilians and also shows, for the first time, loss of heterozygosity in tumor DNA from an acromegaly patient harboring the A299V AIPmut Our findings corroborate previous observations that AIPmut screening should be performed in young patients with SPA.

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.

The genetic background of acromegaly

Acromegaly is caused by a somatotropinoma in the vast majority of the cases. These are monoclonal tumors that can occur sporadically or rarely in a familial setting. In the last few years, novel familial syndromes have been described and recent studies explored the landscape of somatic mutations in sporadic somatotropinomas. This short review concentrates on the current knowledge of the genetic basis of both familial and sporadic acromegaly.

Increased Population Risk of AIP-Related Acromegaly and Gigantism in Ireland

The aryl hydrocarbon receptor interacting protein (AIP) founder mutation R304^* (or p.R304^*; NM_003977.3:c.910C>T, p.Arg304Ter) identified in Northern Ireland (NI) predisposes to acromegaly/gigantism; its population health impact remains unexplored. We measured R304^* carrier frequency in 936 Mid Ulster, 1,000 Greater Belfast (both in NI) and 2,094 Republic of Ireland (ROI) volunteers and in 116 NI or ROI acromegaly/gigantism patients. Carrier frequencies were 0.0064 in Mid Ulster (95%CI = 0.0027–0.013; P = 0.0005 vs. ROI), 0.001 in Greater Belfast (0.00011–0.0047) and zero in ROI (0–0.0014). R304^* prevalence was elevated in acromegaly/gigantism patients in NI (11/87, 12.6%, P < 0.05), but not in ROI (2/29, 6.8%) versus non‐Irish patients (0–2.41%). Haploblock conservation supported a common ancestor for all the 18 identified Irish pedigrees (81 carriers, 30 affected). Time to most recent common ancestor (tMRCA) was 2550 (1,275–5,000) years. tMRCA‐based simulations predicted 432 (90–5,175) current carriers, including 86 affected (18–1,035) for 20% penetrance. In conclusion, R304^* is frequent in Mid Ulster, resulting in numerous acromegaly/gigantism cases. tMRCA is consistent with historical/folklore accounts of Irish giants. Forward simulations predict many undetected carriers; geographically targeted population screening improves asymptomatic carrier identification, complementing clinical testing of patients/relatives. We generated disease awareness locally, necessary for early diagnosis and improved outcomes of AIP‐related disease.