Somatic USP8 Gene Mutations Are a Common Cause of Pediatric Cushing Disease

Genetics of Pituitary Tumours

Pituitary tumours are relatively common in the general population. Most often they occur sporadically, with somatic mutations accounting for a significant minority of somatotroph and corticotroph adenomas. Pituitary tumours can also develop secondary to germline mutations as part of a complex syndrome or as familial isolated pituitary adenomas. Tumours occurring in a familial setting may present at a younger age and can behave more aggressively with resistance to treatment. This chapter will focus on the genetics and molecular pathogenesis of pituitary tumours.

Germline USP8 Mutation Associated With Pediatric Cushing Disease and Other Clinical Features: A New Syndrome

BACKGROUND

Somatic mutations in the ubiquitin-specific peptidase 8 (USP8) gene are common in corticotropinomas of children with Cushing disease (CD). We report a unique patient with a germline USP8 mutation who presented with CD and a constellation of other findings that constitute an intriguing genetic syndrome.

CASE DESCRIPTION

We describe a 16-year-old female with CD, developmental delay, dysmorphic features, ichthyosiform hyperkeratosis, chronic lung disease, chronic kidney disease, hyperglycemia, dilated cardiomyopathy with congestive heart failure, and previous history of hyperinsulinism and partial GH deficiency. She was diagnosed with CD at 14 years old and underwent transsphenoidal surgery. Despite initial improvement, she developed recurrent CD.

METHODS

DNA was extracted from peripheral blood and tumor DNA; whole-exome and Sanger confirmatory sequencing were performed. Immunohistochemistry was performed on the resected adenoma.

RESULTS

A de novo germline heterozygous USP8 mutation (c.2155T>C, p.S719P) in the critical 14-3-3 binding motif hot spot locus of the gene was identified in both the peripheral blood and tumor DNA. Histopathologic evaluation of the resected tumor confirmed an ACTH-secreting adenoma.

CONCLUSION

Somatic USP8 mutations are common in adenomas causing CD, but to date, no germline defects have been reported. We describe a patient with a de novo germline USP8 mutation with recurrent CD and multiple other medical problems. This unique patient informs us of the multitude of signaling events that may be controlled by USP8.

Cushing's disease due to somatic USP8 mutations: a systematic review and meta-analysis

PURPOSE

Cushing's disease (CD) is a severe illness generally caused by microcorticotropinomas (MICs) and in approximately 7-20% of patients by macrocorticotropinomas (MACs). USP8-mutations have been identified as a major genetic cause of CD (~ 50%). Few studies have reported the distribution between MICs-MACs related to USP8-mutations and their genotype-phenotype correlations. Therefore, we aimed to evaluate USP8-mutations in a cohort of MICs-MACs from a unique center and to perform a systematic review and meta-analysis.

METHODS

DNA-tumor-tissues from 47 corticotropinomas (16 MICs and 31 MACs) were sequenced. Clinical-biochemical data, radiological imaging data and remission/recurrence rates were evaluated. In addition, we performed a meta-analysis of nine published series (n = 630).

RESULTS

We identified four different USP8-mutations previously described, in 11 out of 47 (23.4%) corticotropinomas; 8 out of 11 were MACs. The urinary cortisol levels of our patients with corticotrophin USP8-mutated-alleles were lower than those of patients with wild-type (WT) alleles (p ≤ 0.017). The frequency of USP8-mutated-alleles among the series was approximately 30% with a higher prevalence in female-patients (p < 0.1 × 10^-4). Among the 5 series, the remission rates were higher in patients with USP8-mutated-alleles than in those with the USP8-WT-alleles (p < 0.1 × 10^-4).

CONCLUSION

Our data, as well as the retrospective review of CD series associated with USP8-mutated alleles, show heterogeneous findings among the series. Several drawbacks included the lack of a systematic protocol to evaluate these patients before surgery and follow-up. Further prospective studies using a systematic protocol will provide more consistent information about the influence of the corticotropinomas with USP8-mutated alleles on the phenotype, responses to treatment and outcome of patients with CD.

Large Genomic Aberrations in Corticotropinomas Are Associated With Greater Aggressiveness

CONTEXT

Genomic losses/gains are associated with cancer progression and prognosis. In pituitary adenomas, analyses of copy number variations (CNVs) have shown that a subset of adenomas have higher genomic variability. However, whether CNVs are associated with tumor aggressiveness and prognosis has not been determined.

OBJECTIVE

We hypothesized that somatic CNVs of pituitary tumors may play a role in the progression and aggressiveness of pituitary corticotropinomas in children and adolescents.

SAMPLES AND DESIGN

Paired germline and tumor DNA samples from 27 pediatric patients with Cushing disease (CD), were subjected to whole exome sequencing. Somatic CNVs were identified using the ExomeDepth tool. Clinical, histological, and biochemical data from the patients were collected and correlated with the results of the CNV analysis.

RESULTS

Chromosomal instability, involving 23% to 59% of the tumor genome, was noted in 5 of the 27 samples (18.5%). The patients with tumors showing chromosomal instability had similar clinical and biochemical characteristics to the remaining patients, except for tumor size, which was larger (median size 18 mm vs 5.5 mm, P = 0.005). Tumors with chromosomal instability were also associated with a higher rate of invasion of the cavernous sinus (P = 0.029). There was insufficient information on persistence or recurrence of CD to determine whether the risk was higher in those with chromosomal instability.

CONCLUSIONS

A subgroup of corticotropinomas demonstrates chromosomal instability that is associated with markers of aggressiveness of these adenomas. It appears that more genomic gains/losses in a few, rare corticotropinomas may predict poorer prognosis for pediatric patients with CD.

Clinical characteristics and surgical outcome in USP8-mutated human adrenocorticotropic hormone-secreting pituitary adenomas

PURPOSE

somatic mutations in the ubiquitin-specific protease 8 (USP8) gene have recently been described in patients with Cushing's disease (CD). The aim of the study is to verify whether USP8 mutation may predict early and late outcome of pituitary surgery in patients with CD operated at a single institution.

METHODS

We performed a retrospective genetic analysis of 92 adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas. Specimens were screened for USP8 hotspot mutations in the exon 14 with Sanger sequencing. Hormonal and surgical data were compared between USP8 variant carriers and wild-type tumors.

RESULTS

USP8 variants were detected in 22 adenomas (23.9%) with higher prevalence in women (28.9% vs. 5.3% in men; p < 0.05). No significant difference in hormonal levels and tumoral features in relation to USP8 status was observed. Interestingly, USP8-variant carriers were more likely to achieve surgical remission than wild-type adenomas (100% vs. 75.7%; p = 0.01). Conversely, recurrence of CD occurred in 23% of USP8-mutated patients and in 13% of patients with wild-type adenoma. The recurrence-free survival did not differ significantly between the two groups (p = 0.42).

CONCLUSIONS

ACTH-secreting pituitary adenomas carrying somatic USP8 mutations are associated with a greater likelihood of surgical remission in patients operated by a single neurosurgeon. Recurrence rates are not related with USP8-variant status.

Cyclic Cushing's Disease in the Prepubertal Period-A Case Report and Review of Literature

Background: Cyclic Cushing's disease (CD) has been described in about 15% of adult patients with CD. In the pediatric population, diagnosis of CD is rare and cyclic presentations of the disease are not adequately understood or described. Moreover, prepubertal patients usually do not present with the typical signs and symptoms of CD, which can obscure or delay diagnosis. In this paper, we report a case of cyclic CD in a prepubertal age girls whose etiology was a pituitary corticotropinoma. Case presentation: A Caucasian 7.8 year old girl was admitted to pediatric endocrinology for the evaluation of short stature and prior obesity. The patient remained overweight despite significant lifestyle modifications, resulting in 6 kg weight loss during the prior 6 months. The physical exam was notable for precocious adrenarche and thelarche, but difficult to differentiate from steatomastia. Hypothalamo-pituitary-adrenal axis diagnostics, including single diurnal excretion of urinary cortisol, morning ACTH, and serum cortisol levels, were all within normal limits, and MRI of the pituitary gland showed no deviations at this time. Because of the clinical suspicion of cyclic hypercortisolemia, she was referred to our outpatient clinic for follow-up. After 6 months, the patient returned with rapid weight gain, accompanied by nocturnal anxiety, exacerbation of depressive behavior, insomnia and excessive sweating, and was readmitted to the ward for testing. Standard diagnostics confirmed CD and repeat MRI at 8.6 years old showed a microadenoma of 3 × 4 mm in the right side of the anterior pituitary gland. Histopathologic examination described an atypical, densely-granulated pituitary corticotroph adenoma with Ki-67 expression above 3%. Conclusion: Cyclic presentations of CD in the prepubescent age group could cause difficulties in diagnosis because of atypical signs and symptoms, which can be absent in the remission phase. Decreases in height percentiles and velocities obtained from the growth chart, as well as fluctuations in weight, and signs of androgenization can allow the clinician to suspect cycling CD in prepubertal patients. Confirmation of cyclic CD diagnosis is only possible during periods of relapse (hypercortisolemic state) and should be investigated according to the current diagnostic standard.

A personal series of 100 children operated for Cushing's disease (CD): optimizing minimally invasive diagnosis and transnasal surgery to achieve nearly 100% remission including reoperations

Background Transnasal surgery (TNS) is the first choice in the treatment of pediatric Cushing's disease. The question is how can high remission rates be achieved with minimally invasive investigations and TNS whilst avoiding radiotherapy or bilateral adrenalectomy in children. Methods Data from a published series 1 (n=55) of surgeon DKL will be compared with his recent series 2 (n=45) until 2009. All patients were operated by direct transnasal microsurgery. Over time, inferior petrosal sinus sampling (IPSS) was replaced by cavernous sinus sampling (CSS), restricted to unclear cases without increase of salivary cortisol in corticotropin-releasing hormone-test, difficult sellar anatomy or negative magnetic resonance imaging (MRI). Multiple direct intra-operative micro-cytology, micro-doppler and adequate visualization techniques are described. Results In series 1, IPSS was performed in 13 (24%) of whom 46% had false adenoma lateralization. All adenomas could be removed with extensive pituitary exploration. Three patients had early successful re-surgery. In series 2, with more refined MRI and endocrinology, CSS was used in only seven patients (15%) and all micro-adenomas were correctly localized. In three of four patients with persistent cortisol excess, repeat-TNS was necessary and successful. Side effects of TNS were minimal. Recurrence rates were 16% and 11% in series 1 and 2, respectively. Only four of 100 children with invasive adenomas were irradiated, significantly less than in other experienced pediatric centers. Conclusions Thus, 98% remission rate could be achieved with fewer invasive pre-surgical investigations, such as central catheter studies, refined TNS and early repeat-TNS. Repeat-TNS in recurrences minimized the need for irradiation.

Recent advances in understanding corticotroph pituitary tumor initiation and progression

Cushing’s disease is the most frequent form of hypercortisolism and is caused by hypophyseal corticotroph adenomas secreting excessive amounts of adrenocorticotropic hormone. Most of the tumors develop sporadically and only a limited number of corticotroph adenomas have been found to be associated with different neuroendocrine syndromes or with familial isolated pituitary adenomas. The pathogenic mechanisms of corticotroph adenomas are largely unknown, but the discovered aberrant chaperoning activity of heat shock protein 90 on the one hand and the presence of ubiquitin-specific protease 8 mutations on the other hand partially explained the causes of their development. Corticotroph tumors arise initially as benign microadenomas but with time form invasively growing aggressive macroadenomas which can switch to corticotroph carcinomas in extremely rare cases. The mechanisms through which corticotroph tumors escape from glucocorticoid negative feedback are still poorly understood, as are the processes that trigger the progression of benign corticotroph adenomas toward aggressive and malignant phenotypes. This review summarizes recent findings regarding initiation and progression of corticotroph pituitary tumors.

PATHOGENESIS OF CUSHING DISEASE: AN UPDATE ON THE GENETICS OF CORTICOTROPINOMAS

OBJECTIVE

Cushing disease is a rare severe condition caused by pituitary tumors that secrete adrenocorticotropic hormone (ACTH), leading to excessive endogenous glucocorticoid production. Tumors causing Cushing disease, also called corticotropinomas, are typically monoclonal neoplasms that mainly occur sporadically.

METHODS

Literature review.

RESULTS

Cushing disease is very rarely encountered in genetic familial syndromes. Oncogenes and tumor suppressor genes commonly associated with other tumor types are only rarely mutated in this tumor type. The advent of next-generation sequencing led to the identification of a single mutational hotspot in the ubiquitin-specific protease 8 ( USP8) gene in almost half of Cushing disease tumors.

CONCLUSION

The new discoveries showcase a novel mechanism responsible for corticotroph tumorigenesis and ACTH hypersecretion and highlight USP8 and its downstream signaling pathways as potential promising pharmacologic targets for the management of Cushing disease.

ABBREVIATIONS

ACTH = adrenocorticotropic hormone; BRG1 = Brahma-related gene 1; CABLES1 = CDK5 and ABL1 enzyme substrate 1; CD = Cushing disease; CNC = Carney complex; DICER1 = cytoplasmic endoribonuclease III; EGFR = epidermal growth factor receptor; GR = glucocorticoid receptor; IL = interleukin; MEN = multiple endocrine neoplasia; miRNA = microRNA; POMC = proopiomelanocortin; SSTR = somatostatin receptor; USP8 = ubiquitin-specific protease 8.

65 YEARS OF THE DOUBLE HELIX: Endocrine tumour syndromes in children and adolescents

As medicine is poised to be transformed by incorporating genetic data in its daily practice, it is essential that clinicians familiarise themselves with the information that is now available from more than 50 years of genetic discoveries that continue unabated and increase by the day. Endocrinology has always stood at the forefront of what is called today 'precision medicine': genetic disorders of the pituitary and the adrenal glands were among the first to be molecularly elucidated in the 1980s. The discovery of two endocrine-related genes, GNAS and RET, both identified in the late 1980s, contributed greatly in the understanding of cancer and its progression. The use of RET mutation testing for the management of medullary thyroid cancer was among the first and one of most successful applications of genetics in informing clinical decisions in an individualised manner, in this case by preventing cancer or guiding the choice of tyrosine kinase inhibitors in cancer treatment. New information emerges every day in the genetics or system biology of endocrine disorders. This review goes over most of these discoveries and the known endocrine tumour syndromes. We cover key genetic developments for each disease and provide information that can be used by the clinician in daily practice.

The USP8 mutational status may predict long-term remission in patients with Cushing's disease

OBJECTIVE

Almost half of the cases of Cushing's disease (CD) tumours carry recurrent activating somatic mutations in the ubiquitin-specific protease eight gene (USP8). The USP8 mutational status could predict remission in patients with CD, so our objective was to correlate the presence of somatic USP8 mutations with the rate of recurrence after transsphenoidal surgery (TSS) retrospectively.

DESIGN

Biochemical, radiological and clinical data were retrospectively assessed in 48 patients. USP8 mutational status was determined from corticotroph tumour samples. Association between USP8 mutational status, remission and recurrence was investigated.

PATIENTS

Patients with Cushing's disease from a single-centre cohort who underwent TSS between 1991 and 2012.

MEASUREMENTS

Long-term remission and recurrence rate after TSS with at least 6 months follow-up. Biochemical, radiological and clinical data, including sex, age at diagnosis, tumour size and pre-operative hormonal levels. USP8 mutational status.

RESULTS

Patients with USP8 mutant corticotroph tumours (18 of 48; 37%) were diagnosed significantly earlier (mean ± SD 46 ± 10 years vs 53 ± 11 years; P = 0.028) and presented with higher pre-operative 24-hour urinary-free cortisol levels (median IQR μg/24 hours 1174.0, 1184.5 vs 480.0, 405.3; P = 0.045). The incidence of recurrence in a 10-year follow-up was significantly higher in patients with USP8 mutant tumours after the initial remission (58% vs 18% P = 0.026). Recurrence appeared significantly earlier in these patients (months 70, 44-97 95% CI vs 102, 86-119 95% CI; P = 0.019).

CONCLUSION

Recurrence appears to be more frequent and earlier after TSS in patients with USP8 mutant corticotroph tumours.

Genetics of Cushing's Syndrome

The knowledge on the molecular and genetic causes of Cushing's syndrome (CS) has greatly increased in the recent years. Somatic mutations leading to overactive 3',5'-cyclic adenosine monophosphate/protein kinase A and wingless-type MMTV integration site family/beta-catenin pathways are the main molecular mechanisms underlying adrenocortical tumorigenesis. Corticotropinomas are characterized by resistance to glucocorticoid negative feedback, impaired cell cycle control and overexpression of pathways sustaining ACTH secretion. Recognizing the genetic defects behind corticotroph and adrenocortical tumorigenesis proves crucial for tailoring the clinical management of CS patients and for designing strategies for genetic counseling and clinical screening to be applied in routine medical practice.

An update on the genetics of benign pituitary adenomas in children and adolescents

Pituitary adenomas in children and adolescents are rare tumors that often result from a tumor predisposition syndrome. Several inherited causes for pituitary adenomas have been identified in the last few years, including multiple endocrine neoplasia type 1 and 4, Carney's complex, Tuberous sclerosis, DICER1 syndrome, neurofibromatosis type 1, McCune Albright syndrome, familial isolated pituitary adenoma, and pituitary adenoma association due to defects in succinate dehydrogenase genes. Recently, our group discovered X-linked acrogigantism (X-LAG), a new pediatric disorder that is caused by an Xq26.3 genomic duplication (involving the GPR101 gene). Genes that predispose to pediatric Cushing disease, including CABLES1 and USP8, were also recently identified. Genetic screening and counseling of affected or at risk individuals is a key component of their comprehensive care. In this review, we provide an up-to-date discussion on the latest pediatric genetic discoveries associated with pituitary adenomas with a focus on familial syndromes.

Neonatal Cushing Syndrome: A Rare but Potentially Devastating Disease

Neonatal Cushing syndrome (CS) is most commonly caused by exogenous administration of glucocorticoids and rarely by endogenous hypercortisolemia. CS owing to adrenal lesions is the most common cause of endogenous CS in neonates and infants, and adrenocortical tumors (ACTs) represent most cases. Many ACTs develop in the context of a TP53 gene mutation, which causes Li-Fraumeni syndrome. More rarely, neonatal CS presents as part of other syndromes such as McCune-Albright syndrome or Beckwith-Wiedemann syndrome. Management usually includes resection of the primary tumor with or without additional medical treatment, but manifestations may persist after resolution of hypercortisolemia.

USP8 Mutations in Pituitary Cushing Adenomas-Targeted Analysis by Next-Generation Sequencing

Gain-of-function somatic mutations in the ubiquitin specific protease 8 (USP8) gene have recently been reported as a cause of pituitary adenomas in Cushing disease. Molecular diagnostic testing of tumor tissue may aid in the diagnosis of specimens obtained through therapeutic transsphenoidal surgery; however, for small tumors, availability of fresh tissue is limited, and contamination with normal tissue is frequent. We performed molecular testing of DNA isolated from single formalin-fixed and paraffin-embedded (FFPE) tissue sections of 42 pituitary adenomas from patients with Cushing disease (27 female patients and 15 male patients; mean age at surgery, 42.5 years; mean tumor size, 12.2 mm). By Sanger sequencing, we identified previously reported USP8 missense mutations in six tumors. Targeted next-generation sequencing (NGS) revealed known or previously undescribed missense mutations in three additional tumors (two with two different mutations each), with mutant allele frequencies as low as 3%. Of the nine tumors with USP8 mutations (mutation frequency, 21.4%), seven were from female patients (mutation frequency, 25.9%), and two were from male patients (mutation frequency, 13.3%). Mutant tumors were on average 11.4 mm in size, and patients with mutations were on average 43.9 years of age. The overall USP8 mutation frequency in our cohort was lower than in previously described cohorts, and we did not observe USP8 deletions that were frequent in other cohorts. We demonstrate that testing for USP8 variants can be performed from small amounts of FFPE tissue. NGS showed higher sensitivity for USP8 mutation detection than did Sanger sequencing. Assessment for USP8 mutations may complement histopathological diagnosis.

Genetics of Cushing's disease

Cushing's disease (CD) is a rare disabling condition caused by Adrenocorticotropic hormone (ACTH)-secreting adenomas of the pituitary. The majority of corticotropic adenomas are monoclonal and occur sporadically. Only rarely does CD arise in the context of genetic familial syndromes. Targeted sequencing of oncogenes and tumour suppressor genes commonly mutated in other tumours did not identify recurrent mutations. In contrast, next generation sequencing allowed us recently to clarify the genetic basis of CD: we identified somatic driver mutations in the ubiquitin-specific protease 8 (USP8) gene in a significant portion of corticotropinomas. These mutations represent a novel and unique mechanism leading to ACTH excess. Inhibition of USP8 or its downstream signalling pathways could represent a new therapeutic approach for the management of CD. In this review, we will focus on this new evidence and its implication for clinical care of affected patients.

Cell Cycle Regulators and Lineage-Specific Therapeutic Targets for Cushing Disease

Cell cycle proteins are critical to pituitary development, but their contribution to lineage-specific tumorigenesis has not been well-elucidated. Emerging evidence from in vitro human tumor analysis and transgenic mouse models indicates that G1/S-related cell cycle proteins, particularly cyclin E, p27, Rb, and E2F1, drive molecular mechanisms that underlie corticotroph-specific differentiation and development of Cushing disease. The aim of this review is to summarize the literature and discuss the complex role of cell cycle regulation in Cushing disease, with a focus on identifying potential targets for therapeutic intervention in patients with these tumors.

Loss-of-function mutations in the CABLES1 gene are a novel cause of Cushing's disease

The CABLES1 cell cycle regulator participates in the adrenal-pituitary negative feedback, and its expression is reduced in corticotropinomas, pituitary tumors with a largely unexplained genetic basis. We investigated the presence of CABLES1 mutations/copy number variations (CNVs) and their associated clinical, histopathological and molecular features in patients with Cushing's disease (CD). Samples from 146 pediatric (118 germline DNA only/28 germline and tumor DNA) and 35 adult (tumor DNA) CD patients were screened for CABLES1 mutations. CNVs were assessed in 116 pediatric CD patients (87 germline DNA only/29 germline and tumor DNA). Four potentially pathogenic missense variants in CABLES1 were identified, two in young adults (c.532G > A, p.E178K and c.718C > T, p.L240F) and two in children (c.935G > A, p.G312D and c.1388A > G, and p.D463G) with CD; no CNVs were found. The four variants affected residues within or close to the predicted cyclin-dependent kinase-3 (CDK3)-binding region of the CABLES1 protein and impaired its ability to block cell growth in a mouse corticotropinoma cell line (AtT20/D16v-F2). The four patients had macroadenomas. We provide evidence for a role of CABLES1 as a novel pituitary tumor-predisposing gene. Its function might link two of the main molecular mechanisms altered in corticotropinomas: the cyclin-dependent kinase/cyclin group of cell cycle regulators and the epidermal growth factor receptor signaling pathway. Further studies are needed to assess the prevalence of CABLES1 mutations among patients with other types of pituitary adenomas and to elucidate the pituitary-specific functions of this gene.