Loss-of-function (LOF) germline AIP variants are the main genetic cause of familial isolated pituitary adenoma and gigantism. A role for this defect in other neoplasms has been suggested, but remains unclear. We investigated the frequency, associated phenotypes, and in vitro functional effects of germline AIP variants in a cohort of Mexican patients with neuroendocrine neoplasms (NENs). Blood DNA samples from 101 adults (70.3% females) with isolated or syndromic NENs (50 with pituitary neuroendocrine tumors, PitNETs) were analyzed using a next generation sequencing panel. Targeted Sanger screening was carried out in additional family members and tumor samples. Missense and intronic variants were functionally assessed via cycloheximide chase assays or quantitative polymerase chain reaction plus sequence analysis of blood cDNA, as appropriate. Two rare likely benign defects (c.787 + 9C>T and p.T231M), two variants of uncertain significance (p.R106C and p.V291_L292del), one likely pathogenic (LP, p.C238Y), and one pathogenic (p.R304*) variant were found in six cases (5.9%). One individual was diagnosed with multiple gastric NENs and five carried PitNETs. Variant p.V291_L292del produced an unstable protein (P < 0.0001 for half-life curve, compared with wild type) and was reclassified to LP. Loss of heterozygosity in a gastric neuroendocrine tumor and nonsignificantly increased protein stability were observed for p.R106C. No deleterious effects were documented for c.787 + 9C>T. In conclusion, we determined the prevalence of AIP variants in a cohort of NENs and reclassified one VUS to LP. Our findings support the causal association of AIP LOF with PitNETs, but cannot rule out a role for AIP in other NENs.

Carney Complex (CNC) is a rare multiple endocrine neoplasia syndrome, due to PRKAR1A mutation, that causes GH-secreting pituitary adenomas (PA) in 10% of patients. PRKAR1A is not currently analyzed in patients with isolated sporadic or familial PA, in contrast to MEN1 or AIP. We report the case of a young man diagnosed with a PA at age 21 during melanoma follow-up, with a family history of PA. He was initially misdiagnosed with FIPA due to a misclassified AIP mutation, before a final diagnosis of CNC was established. We subsequently retrospectively analysed PRKAR1A in a cohort of patients with PA to assess the relevance of includingPRKAR1A in PA predisposition gene panels. After AIP variant reclassification and whole genome analysis of the patient, we performed a retrospective analysis of the genetic and clinical data of patients who underwent germline genetic testing for hereditary predisposition to PA. Two hundred and twenty patients were included, of whom 16 (7.3%) had a family history of PA, 162 (72.7%) had macro-PA, and 54 (24.6%) had GH- or GH/PRL-secreting PA. Four patients (1.8%) carried pathogenic variants in AIP or MEN1, but none in PRKAR1A. This case underscores the importance of periodically reassessing genetic variants, as reclassification can significantly impact patient management. It also highlights the clinical variability of CNC and the need to screen for CNC features in young patients with acromegaly. Further research is warranted to determine the value ofPRKAR1A testing in isolated GH- and GH/PRL-secreting PA. AIP familial isolated pituitary adenoma (AIP-FIPA) is characterized by an increased risk of pituitary neuroendocrine tumors (PitNETs, also known as pituitary adenomas), including growth hormone (GH)-secreting PitNETs (somatotropinomas), prolactin-secreting PitNETs (prolactinomas), GH and prolactin cosecreting PitNETs (somatomammotropinomas), and clinically nonfunctioning PitNETs (NF-PitNETs). Rarely, thyroid-stimulating hormone (TSH)-secreting PitNETs (thyrotropinomas) are observed. Clinical findings result from excess hormone secretion, lack of hormone secretion, and/or mass effects (e.g., headaches, visual field loss). Within the same family, PitNETs can be of the same or different type. Age of diagnosis in AIP-FIPA is usually in the second or third decade. The diagnosis of AIP-FIPA is established in a proband with a PitNET by identification of a heterozygous germline pathogenic variant in AIP by molecular genetic testing. Treatment of manifestations: AIP-associated pituitary tumors are usually treated in the same manner as those of unknown genetic cause. Standard treatment of GH-producing microadenomas includes medical therapy (somatostatin receptor ligands [SRLs], GH receptor antagonists, and dopamine agonists), surgery, and/or radiotherapy. Large somatotropinomas are treated with transsphenoidal surgery, medical therapy, and/or radiotherapy. Cardiovascular and rheumatologic/orthopedic complications for individuals with acromegaly are managed as in other individuals with acromegaly. Prolactinomas are treated with dopamine agonist therapy or surgery. NF-PitNETs are treated with surgery and, if necessary, radiotherapy. Management of hypopituitarism (due to tumoral compression, surgery, or radiotherapy) should follow standard guidelines for endocrine care. Persons on glucocorticoid replacement therapy need to increase their steroid dose when ill or stressed. Surveillance: In asymptomatic individuals: annual growth assessment and evaluation for signs/symptoms of PitNETs and pubertal development from age four years until adulthood. Although development of new disease in a previously clinically screened person has not been observed in individuals age >30 years, 11 percent of individuals have been diagnosed at age >30 years. Therefore, annual evaluation for signs and symptoms of PitNETs should be carried out until age 30 years and then every five years between ages 30 and 50 years. Annual pituitary function tests (serum IGF-1, prolactin, estradiol/testosterone, LH, FSH, TSH, thyroxine) beginning at age four years until age 30; pituitary MRI at age ten years and repeated (every 5 years has been suggested) or as necessary based on clinical and biochemical parameters until age 30 years. Pituitary MRI can be done in those with clinical or biochemical abnormality from age 30 to 50 years, but screening can be less frequent if laboratory tests are normal. In symptomatic individuals: annual clinical assessment and pituitary function tests (serum IGF-1, spot GH, prolactin, estradiol/testosterone, LH, FSH, TSH, thyroxine, and morning cortisol); if indicated, annual dynamic testing to evaluate for hormone excess or deficiency (e.g., glucose tolerance test, insulin tolerance test); pituitary MRI with frequency depending on clinical status, previous extent of the tumor, and treatment modality. Clinical monitoring of secondary complications of the tumor and/or its treatment (e.g., diabetes mellitus, hypertension, osteoarthritis, hypogonadism, osteoporosis); in those with acromegaly, colonoscopy at age 40 years and repeated every three to ten years depending on the number of colorectal lesions and IGF-1 levels. Evaluation of relatives at risk: Molecular genetic testing for the familial AIP pathogenic variant is appropriate for all at-risk relatives. Apparently asymptomatic individuals found to be heterozygous for a familial AIP pathogenic variant seem to benefit from targeted surveillance: PitNETs identified in asymptomatic individuals are significantly less invasive and are associated with better outcomes compared with PitNETs diagnosed in symptomatic individuals. AIP-FIPA is inherited in an autosomal dominant manner with reduced penetrance. Almost all individuals reported to date with AIP-FIPA have a parent who is also heterozygous for the AIP pathogenic variant; because clinical penetrance of PitNETs in individuals with AIP pathogenic variants is approximately 15%-30%, a heterozygous parent may or may not be affected. Each child of an individual who is heterozygous for an AIP pathogenic variant has a 50% chance of inheriting the pathogenic variant. Once the AIP pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible. As AIP-FIPA demonstrates reduced penetrance, the finding of an AIP pathogenic variant prenatally does not allow accurate prediction of a tumor, the PitNET type, age of onset, prognosis, or availability and/or outcome of treatment.

Heterozygous germline loss-of-function variants in AIP are associated with young-onset growth hormone and/or prolactin-secreting pituitary tumours. However, the pathogenic role of the c.911G > A; p.(Arg304Gln) (R304Q) AIP variant has been controversial. Recent data from public exome/genome databases show this variant is not infrequent. The objective of this work was to reassess the pathogenicity of R304Q based on clinical, genomic, and functional assay data. Data were collected on published R304Q pituitary neuroendocrine tumour cases and from International Familial Isolated Pituitary Adenoma Consortium R304Q cases (n = 38, R304Q cohort). Clinical features, population cohort frequency, computational analyses, prediction models, presence of loss-of-heterozygosity, and in vitro/in vivo functional studies were assessed and compared with data from pathogenic/likely pathogenic AIP variant patients (AIPmut cohort, n = 184). Of 38 R304Q patients, 61% (23/38) had growth hormone excess, in contrast to 80% of AIPmut cohort (147/184, P < .001). R304Q cohort was older at disease onset and diagnosis than the AIPmut cohort (median [quartiles] onset: 25 y [16-35] vs 16 y [14-23], P < .001; median [quartiles] diagnosis: 36 y [24-44] vs 21 y [15-29], P < .001). R304Q is present in gnomADv2.1 (0.31%) and UK Biobank (0.16%), including three persons with homozygous R304Q. No loss-of-heterozygosity was detected in four R304Q pituitary neuroendocrine tumour samples. In silico predictions and experimental data were conflicting. Evidence suggests that R304Q is not pathogenic for pituitary neuroendocrine tumour. We recommend changing this variant classification to likely benign and do not recommend pre-symptomatic genetic testing of family members or follow-up of already identified unaffected individuals with the R304Q variant.

Genetic tests are part of the routine clinical approach to syndromic and nonsyndromic phenotypes of neuroendocrine neoplasms (NENs). Current data on phenotype-genotype associations in NENs, however, do not accurately represent all populations. To describe the frequency, inventory, and clinical associations of germline defects associated with multiple types of NENs in a Mexican cohort. Blood DNA from Mexican adults with NENs was analyzed with a 53-gene next-generation sequencing panel developed ad hoc (n = 90) or Sanger sequencing (n = 2). Single nucleotide variants, indels, and structural variants were identified, classified, and subjected to orthogonal confirmation. When possible, tumor samples and blood DNA from additional family members were tested using Sanger sequencing. Ninety-two probands (70.7% women, 51.5% sporadic) were included; 16 carried pathogenic or likely pathogenic (P/LP) variants and were significantly younger at disease onset than the rest (29.6 ± 10.7 vs 40 [21.5-51.5] years, P = .0384). Likely driving variants were identified in three-quarters of Von Hippel Lindau syndrome cases, one-third of multiple endocrine neoplasia (MEN) type 1, one-quarter of early-onset acromegaly/gigantism, and individual cases of Cushing's disease, MEN2A, and medullary thyroid carcinoma. One patient with clinical MEN1 associated with an SDHA variant and 1 with a pituitary tumor and neurofibromatosis type 1 were also identified. Probands with familial disease were more likely to carry P/LP variants than sporadic cases (26.7 vs 8.5%, P = .0282). P/LP variants were identified in 17.4% of individuals with NENs. Our research provides a view of the landscape of NEN drivers in a population not previously characterized.

Pituitary gigantism is a rare manifestation of chronic growth hormone (GH) excess that begins before closure of the growth plates. Nearly half of patients with pituitary gigantism have an identifiable genetic cause. X-linked acrogigantism (X-LAG; 10% of pituitary gigantism) typically begins during infancy and can lead to the tallest individuals described. In the 10 years since its discovery, about 40 patients have been identified. Patients with X-LAG usually develop mixed GH and prolactin macroadenomas with occasional hyperplasia that secrete copious amounts of GH, and frequently prolactin. Circulating GH-releasing hormone is also elevated in a proportion of patients. X-LAG is caused by constitutive or sporadic mosaic duplications at chromosome Xq26.3 that disrupt the normal chromatin architecture of a topologically associating domain (TAD) around the orphan G-protein-coupled receptor, GPR101. This leads to the formation of a neo-TAD in which GPR101 overexpression is driven by ectopic enhancers ("TADopathy"). X-LAG has been seen in 3 families due to transmission of the duplication from affected mothers to sons. GPR101 is a constitutively active receptor with an unknown natural ligand that signals via multiple G proteins and protein kinases A and C to promote GH/prolactin hypersecretion. Treatment of X-LAG is challenging due to the young patient population and resistance to somatostatin analogs; the GH receptor antagonist pegvisomant is often an effective option. GH, insulin-like growth factor 1, and prolactin hypersecretion and physical overgrowth can be controlled before definitive adult gigantism occurs, often at the cost of permanent hypopituitarism.