DICER1 Syndrome – new mutations, novel phenotypes and unexpected mechanisms

DICER1 syndrome is a rare tumour predisposition syndrome with an autosomal dominant inheritance pattern that is characterised by a unique spectrum of rare to very rare tumours and dysplastic lesions. The prototypic tumour of the syndrome is pleuropulmonary blastoma, a rare mixed-pattern sarcoma of the lung. Other tumours prominently featured in the syndrome include ovarian Sertoli-Leydig cell tumour, paediatric cystic nephroma, and embryonal rhabdomyosarcoma of the uterine cervix, but the syndrome also includes more well-known entities such as multinodular goitre (MNG). DICER1 syndrome predominantly affects young infants and children, but first phenotypic expression occasionally extends into adulthood. Loss-of-function variants in DICER1, a gene that encodes for a member of the microRNA biogenesis machinery, was identified as the underlying genetic cause of the syndrome in 2009. Later, so-called "hotspot" missense mutations within the RNase IIIb domain of DICER1 began to emerge as characteristic somatic events in syndrome-related tumours. Subsequent research efforts, including those that comprise this thesis, have focused on further defining the DICER1 syndrome phenotype, characterising the types and distributions of genetic alterations found within the DICER1 gene, determining the effect of identified mutations on microRNA processing, and elucidating the mechanisms that underpin DICER1-related tumourigenesis. The approaches used in this thesis investigation included investigative sequencing of DICER1 in various tumour types to assess their relation to the syndrome. This led to the addition of 6 entities to the syndrome phenotype that were not previously recognised to be part of the syndrome, including the exceptionally rare pituitary gland tumour, pituitary blastoma (PitB). The employment of deep sequencing and high-sensitivity sequencing techniques allowed us to recognise that clonal distributions of hotspot mutations characterise the nodular architecture of MNG, and that rare mosaic distributions of RNase IIIb hotspot mutations predispose to development of an unusually high number of DICER1-related tumours at especially young ages in children. Thorough molecular profiling of the transcriptome and miRNome of PitB relative to normal adult and normal fetal pituitary revealed a drastic and distinct alteration in expression of miRNAs within the tumours. We observed not only a decrease in expression of miRNAs derived from the 5' arm of the miRNA hairpin precursors, but also a relative increase in the preponderance of those from the 3' arm. Furthermore, preliminary evidence suggests a possible oncofetal signature in PitBs, which may represent an oncogenic switch at the root of PitB tumourigenesis. Taken together, the results presented in this thesis represent significant contributions towards the clinical and molecular characterisation of the DICER1 syndrome.Le syndrome DICER1 est un syndrome rare de prédisposition au développement de tumeurs suivant un mode de transmission dominant. Ce syndrome est caractérisé par un éventail unique de lésions dysplastiques et de tumeurs allant de rares à très rares. La tumeur prototype du syndrome est le blastome pleuropulmonaire, une forme mixte de sarcome du poumon. D'autres tumeurs qui sont notablement représentées dans ce syndrome incluent la tumeur à cellules de Sertoli-Leydig, le néphrome kystique juvénile ainsi que le rhabdomyosarcome embryonnaire du col de l'utérus; le syndrome inclut aussi d'autres entités bien connues tel le goitre multinodulaire. Le syndrome DICER1 affecte principalement les nourrissons et les enfants, mais les premiers symptômes physiques ne se manifestent parfois qu'à l'âge adulte. En 2009, des variantes causant une perte de fonction dans DICER1, un gène encodant un membre de la machinerie de biogenèse des microARNs, furent identifiées comme étant la cause génétique sous-jacente du syndrome. Des mutations ciblées dans le domaine RNase IIIb de la protéine DICER1 se révélèrent ensuite comme étant des événements somatiques typiques dans les tumeurs reliées au syndrome. Les efforts de recherche subséquents, incluant le travail présenté dans cette thèse, se sont concentrés à mieux définir les phénotypes reliés au syndrome, à caractériser le type et la distribution des altérations génétiques dans le gène DICER1, à déterminer l'effet des mutations identifiées sur la fabrication des microARNs, et à élucider les mécanismes de tumorigenèse spécifiques au syndrome DICER1. La stratégie utilisée dans cette thèse est basée sur le séquençage de DICER1 chez plusieurs types de tumeurs pour évaluer leur relation avec le syndrome. Dû à cet effort, six nouvelles entités furent ajoutées à la liste des phénotypes associés au syndrome qui n'étaient pas précédemment reconnues comme telles, incluant le très rare blastome pituitaire. L'utilisation du séquençage en profondeur ainsi que de techniques de séquençage à haute sensibilité nous ont permis de reconnaitre qu'une distribution clonale de mutations ciblées est caractéristique de l'architecture nodulaire des goitres multinodulaires. Nous avons aussi découvert que de rares distributions mosaïques de mutations ciblées dans le domaine RNaseIIIb prédisposent au développement d'un nombre exceptionnellement élevé de tumeurs DICER1, particulièrement chez les enfants en bas âge. Un profilage moléculaire minutieux du transcriptome et du MiRNome de blastomes pituitaires relatifs aux profils de glandes pituitaires fœtales et adultes normales ont révélé des altérations drastiques distinctives dans l'expression des microARNs des tumeurs. En plus d'une diminution de l'expression des microARNs dérivés de la branche 5' des précurseurs à structure en épingle à cheveux, nous avons aussi observé une augmentation relative dans l'abondance de ceux dérivés de la branche 3'. De plus, nos données préliminaires suggèrent une signature oncofœtale potentielle dans les blastomes pituitaires, ce qui pourrait représenter l'élément oncogénique déclencheur à la base du processus de tumorigenèse des blastomes pituitaires. Dans leur ensemble, les résultats présentés dans cette thèse représentent une contribution significative à la caractérisation clinique et moléculaire du syndrome DICER1

Atlas der Alpenflora / Meergrauer Steinbrech

Magasság: 1300-2700 M.Előfordulási hely: Schweiz bis Oesterr. u. Steierm., trockene StellenVirágzás: Juni, Jul

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

Embryonal rhabdomyosarcoma of the uterine corpus : a clinicopathological and molecular analysis of 21 cases highlighting a frequent association with DICER1 mutations

Herein we evaluated a series of 21 embryonal rhabdomyosarcomas of the uterine corpus (ucERMS), a rare neoplasm, to characterize their morphology, genomics, and behavior. Patients ranged from 27 to 73 (median 52) years and tumors from 4 to 15 (median 9) cm, with extrauterine disease noted in two. Follow-up (median 16 months) was available for 14/21 patients; nine were alive and well, four died of disease, and one died from other causes. Most tumors (16/21) showed predominantly classic morphology, comprised of alternating hyper- and hypocellular areas of primitive small cells and differentiating rhabdomyoblasts in a loose myxoid/edematous stroma. A cambium layer was noted in all; seven had heterologous elements (six with fetal-type cartilage) and eight displayed focal anaplasia. The remaining five neoplasms showed only a minor component (<= 20%) of classic morphology, with anaplasia noted in four and tumor cell necrosis in three. The most frequent mutations detected were in DICER1 (14/21), TP53 (7/20), PI3K/AKT/mTOR pathway (7/20), and KRAS/NRAS (5/20). Copy-number alterations were present in 10/19 tumors. Overall, 8/14 DICER1-associated ucERMS showed concurrent loss of function and hotspot mutations in DICER1, which is a feature more likely to be seen in tumors associated with DICER1 syndrome. Germline data were available for two patients, both DICER1 wild type (one with concurrent loss of function and hotspot alterations). DICER1-associated ucERMS were more likely to show a classic histological appearance including heterologous elements than DICER1-independent tumors. No differences in survival were noted between the two groups, but both patients with extrauterine disease at diagnosis and two with recurrences died from disease. As no patients had a known personal or family history of DICER1 syndrome, we favor most DICER1-associated ucERMS to be sporadic