Prashant Chittiboina

Pituitary adenomas constitute up to 20% of primary brain tumors, yet somatic mutations are only found in 15% of pituitary adenomas. Epigenomic dysregulation has been proposed as a tumorigenic mechanism in pituitary adenomas causing Cushing’s disease (CD). We created paired datasets of human CD adenomas and en-route margin adult human pituitary glands, and assayed their chromatin accessibility, DNA methylation, transcriptomic, proteomic, and phospho-proteomic landscapes. In CD adenomas, we found epigenetic reactivation of a neurodevelopmental phosphoprotein program typically lost in the postnatal pituitary gland. CD cells overexpressed PPP1R17 , an endogenous inhibitor of the protein phosphatase PP2A. Mechanistically, PPP1R17 overexpression in normal murine pituitary cells recapitulated the adenoma phenotype, and the resulting hyperproliferation was reversed in a PP2A-dependent manner by fingolimod, an FDA-approved small molecule, both in vitro and in vivo. Our findings highlight kinase-phosphatase imbalance as a targetable mechanism in CD.

Purpose: Neurofibromatosis type 2-related schwannomatosis (NF2-SWN) is an autosomal dominant tumor syndrome with complete penetrance and variable expressivity. Underlying patterns of disease burden and severity are largely unexplained. Methods: We comprehensively phenotyped 168 NF2-SWN patients over a mean duration of 4.5 years. We used a custom sequencing panel of NF2 and schwannomatosis genes to identify germline (n=166) and somatic variants in tumors (n=37). An optimized composite severity (CSS) score based on clinical and radiological data was created to analyze the effect of genetic variants on phenotype. Results: We found significant variable expressivity not explainable by demographic variables. Germline variants included premature termination (42%), splice-site (18%), and large deletions (16%). The CSS successfully predicted worsening clinical function in patients. Unsupervised clustering of clinical data revealed distinct phenotypic clusters that corresponded to CSS. Mosaicism, however, was not associated with CSS or any other disease severity marker. CSS was significantly associated with germline variant location along the NF2 locus. Specifically, FERM-F1 and the α-helical variants were associated with increased disease severity. Within tumors, germline variants with severe effects on merlin acquired milder somatic second-hits at the NF2 locus. Conclusion: We identified a second-hit modifier to the Mendelian first-hit: severe germline variants were associated with milder somatic variants, and vice versa. This phenomenon partly explains the variable expressivity in NF2-SWN. Context Summary: Neurofibromatosis type 2-related schwannomatosis (NF2-SWN) displays striking variability in tumor burden and clinical severity, but the biological basis for this heterogeneity has remained unclear. Using deep longitudinal phenotyping, whole-neuroaxis imaging, and integrated germline-somatic genomic analysis, we show that germline NF2 variant position determines the allowable somatic ‘second hits’ that can give rise to tumors. These data support a merlin-dosage model in which tumorigenesis likely occurs only within an intermediate range of merlin function, bounded by insufficiently tumorigenic and lethal levels on each side. These findings shed light on long-standing inconsistencies in genotype-phenotype relationships in NF2-SWN and help provide a mechanistic basis for predicting disease severity.

Background and objectives: The onset of hearing loss due to vestibular schwannomas (VS) is inevitable but does not correlate with the size of the tumor. In patients with Neurofibromatosis Type 2 (NF2) and VS, we previously found an association between pre-contrast fluid-attenuated inversion recovery magnetic resonance imaging (FLAIR MRI) signal in the labyrinth and hearing loss. Here, we asked whether FLAIR hyper-intensity could serve as a predictive biomarker for hearing loss in NF2 patients with VS. Methods: A prospective longitudinal study (NCT00598351) of NF2 enrolled 168 subjects between 2008 and 2013. This study included 34 patients with small VS (total volume ≤ 500mm ³ ). Middle fossa decompression surgery ( n = 4 patients) was provided via a standard-of-care trial (NCT00060541). Results: From 34 eligible subjects (mean age 26.8y) with NF2 and small VS, 53 ears met inclusion criteria. Abnormal hearing was recorded in 18 ears at study entry; all 18 ears had FLAIR hyper-intensity. Of the 35 ears with normal hearing, 16 had FLAIR hyper-intensity at study entry, 6 (37.5%) of which developed new hearing loss (median time to hearing loss of 4.45 years). Conversion to FLAIR hyper-intensity occurred in 11 ears, 3 of which proceeded to hearing loss. No hearing loss developed in the eight ears that remained FLAIR negative. FLAIR conversion has high sensitivity (1·00, 95% CI 0·39–1) and negative predictive value (1·00, 95% CI 0·63–1) for new-onset hearing loss. In 4 patients undergoing middle fossa decompression surgery, we found that surgery stabilized hearing but did not reverse FLAIR hyperintensity. Conclusions: Our findings suggest that intralabyrinthine FLAIR hyper-intensity is a sensitive, non-invasive biomarker for hearing loss related to VS. Hearing decline followed FLAIR hyper-intensity by approximately 4 years but was absent in ears with normal FLAIR signal. Trial registration: Registry: ClinicalTrials.gov, TRN: NCT00060541, Registration date: 4 June 2003.

Context: Patients with multiple endocrine neoplasia type 1 (MEN1) are genetically predisposed to developing tumors of the parathyroid, pancreas, and anterior pituitary. While widespread genetic testing has increased early diagnoses, the value of radiological surveillance for pituitary adenomas in these patients remains unclear. Objective: To investigate the impact of pituitary magnetic resonance imaging (MRI) findings on patient management in MEN1. Design: Retrospective longitudinal cohort study. Setting: NIH Clinical Center. Patients: Genetically confirmed MEN1 evaluated between 1977 and September 2024. Measures: Cumulative proportion and rate of intervention for nonfunctional adenomas. Results: Three hundred twenty patients with a mean follow-up duration of 14 ± 12 years were identified. One hundred eighty-two out of 320 patients (57%) had pituitary adenomas, of whom 95/182 (52%) had nonfunctional adenomas. All patients with adenoma had biochemical evaluation at the time of pituitary MRI. There were 21/95 (22%) patients with nonfunctional adenomas that needed an intervention throughout their follow-up. The rate of intervention per 100 patient-years for nonfunctional adenomas was 3.1% (confidence interval 2.0-4.7%). All patients with nonfunctional adenoma who required an intervention reported symptoms or had an abnormal pituitary function test. Tumor volume of 38/48 (79%) nonfunctional adenomas followed over a mean of 8.3 ± 6.1 years remained stable. Only 42/518 (8.1%) MRIs for nonfunctional adenomas were prompted by clinical or biochemical abnormalities. Individualized imaging could have avoided approximately 4 MRIs per patient with nonfunctional microadenoma over their follow-up. Conclusion: In an overwhelming majority of patients with MEN1, radiological surveillance for nonfunctional pituitary adenomas offers minimal added benefit beyond patient-reported symptoms and pituitary function testing.