Extraskeletal chondroma of the toe in a child with DICER1 tumor predisposition syndrome: support for a dominant negative mechanism

DICER1 tumor predisposition syndrome is a pleiotropic disorder that gives rise to various mainly pediatric-onset lesions. We report an extraskeletal chondroma (EC) of the great toe occurring in a child who, unusually, carries a germline "hotspot" missense DICER1 variant rather than the more usual loss-of-function (LOF) variant. No heterozygous LOF allele was identified in the EC. We demonstrate this variant impairs 5p cleavage of precursor-miRNA (pre-miRNA) and competes with wild-type (WT) DICER1 protein for pre-miRNA processing. These results suggest a mechanism through which a germline RNase IIIb variant could impair pre-miRNA processing without complete LOF of the WT DICER1 allele.

Fetal Type Morphologies Suggest the Presence of DICER1 Hotspot Mutations in Non-small Cell Lung Cancer

Germline and somatic pathogenic variants (PVs) in DICER1 , encoding a miRNA biogenesis protein, are associated with a wide variety of highly specific pathologic entities. The lung tumors pleuropulmonary blastoma, pulmonary blastoma (PB), and well-differentiated fetal lung adenocarcinoma (WDFLAC) are all known to harbor DICER1 biallelic variants (loss of function and/or somatic hotspot missense mutations), and all share pathologic features reminiscent of the immature lung. However, the role of DICER1 PVs in non-small cell lung cancer (NSCLC) is relatively unknown. Here, we aimed to establish the spectrum of lung pathologies associated with DICER1 hotspot PVs and to compare the mutational landscape of DICER1 -mutated NSCLC with and without hotspots. We queried DNA sequencing data from 12,146 NSCLCs featuring somatic DICER1 variants. 235 (1.9%) cases harboring ≥ 1 DICER1 PV were found and 9/235 (3.8%) were DICER1 hotspot-positive cases. Histologic review of DICER1 hotspot-positive cases showed that all but one tumor were classified as within the histologic spectrum of PB/WDFLAC, whereas all the DICER1 non-hotspot double variants were classified as lung adenocarcinomas, not otherwise specified. Comparison between the mutational landscape of DICER1 hotspot-positive and hotspot-negative cases revealed a higher frequency of CTNNB1 mutations in the hotspot-positive cases (5/9 vs. 2/225; P <0.00001). We conclude that DICER1 somatic hotspots are not implicated in the most common forms of NSCLC but rather select for morphologic features of lung tumor types such as PB and WDFLAC. As a corollary, cases showing this tumor morphology should undergo testing for DICER1 variants, and if positive, genetic counseling should be considered.

Reclassification of two germline DICER1 splicing variants leads to DICER1 syndrome diagnosis

DICER1 syndrome is an inherited condition associated with an increased risk of developing hamartomatous and neoplastic lesions in diverse organs, mainly at early ages. Germline pathogenic variants in DICER1 cause this condition. Detecting a variant of uncertain significance in DICER1 or finding uncommon phenotypes complicate the diagnosis and can negatively impact patient care. We present two unrelated patients suspected to have DICER1 syndrome. Both females (aged 13 and 15 years) presented with multinodular goiter (thyroid follicular nodular disease) and ovarian tumours. One was diagnosed with an ovarian Sertoli-Leydig cell tumour (SLCT) and the other, with an ovarian juvenile granulosa cell tumour, later reclassified as a retiform variant of SLCT. Genetic screening showed no germline pathogenic variants in DICER1. However, two potentially splicing variants were found, DICER1 c.5365-4A>G and c.5527+3A>G. Also, typical somatic DICER1 RNase IIIb hotspot mutations were detected in the thyroid and ovarian tissues. In silico splicing algorithms predicted altered splicing for both germline variants and skipping of exon 25 was confirmed by RNA assays for both variants. The reclassification of the ovarian tumour, leading to recognition of the association with DICER1 syndrome and the characterization of the germline intronic variants were all applied to recently described DICER1 variant classification rules. This ultimately resulted in confirmation of DICER1 syndrome in the two teenage girls.

DICER1 platform domain missense variants inhibit miRNA biogenesis and lead to tumor susceptibility

The endoribonuclease DICER1 plays an essential role in the microRNA (miRNA) biogenesis pathway, cleaving precursor miRNA (pre-miRNA) stem-loops to generate mature single-stranded miRNAs. Germline pathogenic variants (GPVs) in DICER1 result in DICER1 tumor predisposition syndrome (DTPS), a mainly childhood-onset tumor susceptibility disorder. Most DTPS-causing GPVs are nonsense or frameshifting, with tumor development requiring a second somatic missense hit that impairs the DICER1 RNase IIIb domain. Interestingly, germline DICER1 missense variants that cluster in the DICER1 Platform domain have been identified in some persons affected by tumors that also associate with DTPS. Here, we demonstrate that four of these Platform domain variants prevent DICER1 from producing mature miRNAs and as a result impair miRNA-mediated gene silencing. Importantly, we show that in contrast to canonical somatic missense variants that alter DICER1 cleavage activity, DICER1 proteins harboring these Platform variants fail to bind to pre-miRNA stem-loops. Taken together, this work sheds light upon a unique subset of GPVs causing DTPS and provides new insights into how alterations in the DICER1 Platform domain can impact miRNA biogenesis.

Abstract 3522: DICER1 Platform domain missense variants led to tumor susceptibility via failure of precursor miRNA binding

DICER1 is a key protein in the micro(mi)RNA biogenesis pathway responsible for cleaving precursor (pre)-miRNA stemloops with its RNase IIIa and IIIb domains into mature single stranded miRNAs. DICER1 syndrome is a pleiotropic tumor predisposition syndrome in which clinical manifestations are normally first seen during childhood. This genetic disorder is defined by the presence of inherited or de novo germline pathogenic variants (GPVs) in the DICER1 gene. While many germline loss of function variants fail to generate DICER1 protein, a subset of patients has germline missense variants that are predicted to produce full-length DICER1 protein that cluster in the DICER1 Platform domain, a region that plays a role in binding to the 5’ phosphate of pre-miRNA stemloops. Due to the uncertainty surrounding the pathogenicity of missense variants in DICER1 syndrome, clinical actionability can be limited. To determine how Platform mutations predispose to DICER1 syndrome we characterized a number of these variants using in vitro pre-miRNA binding and cleavage assays. Interestingly, four of these variants displayed impaired pre-miRNA binding and processing, with three of them localizing to a hydrophobic pocket in the Platform domain. In keeping with in vitro results, DICER1 mutants displayed impaired miRNA processing when introduced into mesenchymal stem cells. Furthermore, we identified a second somatic hit in the RNase IIIb domain of DICER1 in thyroid nodular hyperplasia DNA from a patient affected by one of these variants. Taken together, these results identify a key region in the DICER1 protein that is essential for pre-miRNA processing and help the classification of these germline variants as pathogenic to ensure proper clinical management of affected patients. Additionally, these results provide insight on the molecular basis involved in DICER1 syndrome predisposition.

Citation Format: Dylan Pelletier, Anne-Laure Chong, Sophie Albert, Marc Fabian, William Foulkes. DICER1 Platform domain missense variants led to tumor susceptibility via failure of precursor miRNA binding. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3522.

Genomic characterization of DICER1-associated neoplasms uncovers molecular classes

DICER1 syndrome is a tumor predisposition syndrome that is associated with up to 30 different neoplastic lesions, usually affecting children and adolescents. Here we identify a group of mesenchymal tumors which is highly associated with DICER1 syndrome, and molecularly distinct from other DICER1-associated tumors. This group of DICER1-associated mesenchymal tumors encompasses multiple well-established clinicopathological tumor entities and can be further divided into three clinically meaningful classes designated "low-grade mesenchymal tumor with DICER1 alteration" (LGMT DICER1), "sarcoma with DICER1 alteration" (SARC DICER1), and primary intracranial sarcoma with DICER1 alteration (PIS DICER1). Our study not only provides a combined approach to classify DICER1-associated neoplasms for improved clinical management but also suggests a role for global hypomethylation and other recurrent molecular events in sarcomatous differentiation in mesenchymal tumors with DICER1 alteration. Our results will facilitate future investigations into prognostication and therapeutic approaches for affected patients.

Somatic tumour testing establishes that bilateral DICER1-associated ovarian Sertoli-Leydig cell tumours represent independent primary neoplasms

AIMS

Sertoli-Leydig cell tumours (SLCTs) are rare ovarian neoplasms that are commonly associated with somatic or germline DICER1 mutations, especially when of the moderately or poorly differentiated type. A large majority are unilateral, but bilateral neoplasms have been reported, sometimes in the context of germline DICER1 mutations (DICER1 syndrome). It is currently unknown whether these represent independent neoplasms or metastasis from one ovary to the other and we aimed to elucidate this.

METHODS AND RESULTS

We report three cases of bilateral ovarian SLCT (all in patients with DICER1 syndrome) and review all reported cases of bilateral neoplasms. In the three cases (all moderately or poorly differentiated neoplasms), the time interval between the discovery of the tumours in each ovary ranged from 2.7 years to 6 years. In all cases, different DICER1 somatic hotspot mutations within the two tumours provided definitive proof that they represent independent neoplasms; this may be important clinically. Our literature review revealed that, when this information was available, all patients with bilateral SLCT had a germline DICER1 mutation.

CONCLUSIONS

Bilateral ovarian SLCTs represent independent rather than metastatic neoplasms, and essentially always occur in the context of DICER1 syndrome.

Proton Density MRI Increases Detection of Cervical Spinal Cord Multiple Sclerosis Lesions Compared with T2-Weighted Fast Spin-Echo

BACKGROUND AND PURPOSE

There is a paucity of literature that supports the Consortium of Multiple Sclerosis Centers guideline that proton density MR imaging is a core spinal cord sequence. We hypothesized that proton density fast spin-echo imaging is superior to T2 fast spin-echo MR imaging for the detection of cervical cord MS lesions. This study compared the detection rate and conspicuity of cervical cord MS lesions on sagittal 1.5T proton density fast spin-echo and T2 fast spin-echo MR imaging.

MATERIALS AND METHODS

One hundred consecutive patients with MS imaged with 1.5T sagittal proton density fast spin-echo and T2 fast spin-echo cervical cord MR imaging between September 2012 and October 2013 were retrospectively included. The number of MS lesions detected on each sequence was recorded; conspicuity was assessed quantitatively with the lesion-to-cord contrast ratio and lesion-contrast-to-noise ratio. Statistical analysis was performed by using the Wilcoxon signed rank test.

RESULTS

Seventy-eight patients had MS cord lesions detected. Proton density fast spin-echo imaging detected a greater number of lesions (n = 181) compared with T2 fast spin-echo imaging (n = 137, P < .001). Fifteen patients (19%) with abnormal findings on proton density fast spin-echo imaging had normal findings on T2 fast spin-echo imaging; no patient with abnormal T2 fast spin-echo imaging findings had normal proton density fast spin-echo imaging findings. Although proton density fast spin-echo and T2 fast spin-echo imaging had similar lesion-to-cord contrast ratios (proton density fast spin-echo, 0.32 ± 0.01, versus T2 fast spin-echo, 0.33 ± 0.01; P = .43), proton density fast spin-echo had greater lesion-contrast-to-noise ratio (proton density fast spin-echo, 82 ± 3.0, versus T2 fast spin-echo, 64 ± 2.6; P < .001).

CONCLUSIONS

Proton density fast spin-echo imaging is superior to T2 fast spin-echo MR imaging for the detection of cervical cord MS lesions. Proton density fast spin-echo detects cord lesions in patients in whom T2 fast spin-echo findings appear normal. This study forms the evidentiary base for the current Consortium of Multiple Sclerosis Centers guideline that proton density imaging is a core spinal cord sequence.

Invasive pneumococcal disease in children in Ireland--the anticipated benefit of conjugate pneumococcal vaccination

BACKGROUND

Streptococcus pneumoniae is an important cause of childhood illness. Recently a safe and effective 7-valent conjugate pneumococcal vaccine for children has been licensed in the EU.

AIMS

To calculate the incidence of invasive pneumococcal disease (IPD) in children in Ireland, to estimate the burden of disease and to anticipate the protective effect of the conjugate vaccine.

METHODS

Retrospective review of data from children with IPD.

RESULTS

Ninety-six cases of IPD in 95 children including two related deaths were identified. All childhood IPD incidence was estimated at 10.6/100,000. We anticipate that the 7-valent conjugate vaccine could prevent up to 90% of sepsis and up to 82.5% of meningitis cases.

CONCLUSIONS

IPD is an important cause of mortality and morbidity in children in Ireland. Routine use of conjugate pneumococcal vaccine would have a significant impact on pneumococcal disease, especially in vaccinated children but also in unvaccinated children and older adults.

The sinister significance of dysphagia

BACKGROUND

The majority of patients presenting with oesophageal cancer have symptoms for more than three months and advanced disease at presentation. Most appear unaware of the significance of dysphagia as a symptom. Cancer awareness programmes focus on symptoms such as lumps and bleeding.

AIM

To sample the level of public awareness of the potentially sinister significance of the symptom of dysphagia.

METHODS

A community survey was conducted using a questionnaire to evaluate the subjects' impression of the significance of dysphagia, and compare it with their perception of the significance of breast lump. Patients were stratified to male and female, under and over 45 years.

RESULTS

There were 164 subjects interviewed. Seventy-five per cent stated that they would visit their doctor within one week of developing dysphagia compared with 87 per cent questioned about a breast lump (96 per cent females, 80 per cent males). Only 17 per cent felt that cancer was a probable explanation for dysphagia compared with 80 per cent who would consider cancer a likely cause of breast lump.

CONCLUSION

There is evident need of an awareness programme of the potential significance of dysphagia if prognosis for oesophageal cancer is to be improved.

Plastic bowing of the forearm in the more mature skeleton

An 18 year old male suffered plastic bowing of both forearm bones following an industrial accident in which his forearm was caught by an electric hoist. Plastic bowing of both the radius and ulna occurred. This deformity, usually seen in children, was produced by an unusual set of circumstances, with a transverse force being applied for a considerable time. All four cases of 'adult' plastic bowing deformity have been the result of industrial accidents and were always the result of a transverse force acting upon the limb. Although, initially, after manipulation there was only minimal improvement in range of movement, progressive improvement was achieved with physiotherapy. In the present case early mobilization resulted in a good functional outcome for the patient.