Publications by authors named "Elisabetta Flex"

43 Publications

A Rare Case of Brachyolmia with Amelogenesis Imperfecta Caused by a New Pathogenic Splicing Variant in .

Genes (Basel) 2021 Sep 12;12(9). Epub 2021 Sep 12.

Medical Genetics Unit, University and Hospital of Perugia, 06129 Perugia, Italy.

In recent years, a rare form of autosomal recessive brachyolmia associated with amelogenesis imperfecta (AI) has been described as a novel nosologic entity. This disorder is characterized by skeletal dysplasia (e.g., platyspondyly, short trunk, scoliosis, broad ilia, elongated femoral necks with coxa valga) and severe enamel and dental anomalies. Pathogenic variants in the latent transforming growth factor-β binding protein 3 () gene have been found implicated in the pathogenesis of this disorder. So far, biallelic pathogenic variants have been identified in less than 10 families. We here report a young boy born from consanguineous parents with a complex phenotype including skeletal dysplasia associated with aortic stenosis, hypertrophic cardiomyopathy, hypodontia and amelogenesis imperfecta caused by a previously unreported homozygous splice site variant. We also compare the genotypes and phenotypes of patients reported to date. This work provides further evidence that brachyolmia with amelogenesis imperfecta is a distinct nosologic entity and that variations in are involved in its pathogenesis.
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http://dx.doi.org/10.3390/genes12091406DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8470690PMC
September 2021

Hyperactive HRAS dysregulates energetic metabolism in fibroblasts from patients with Costello syndrome via enhanced production of reactive oxidizing species.

Hum Mol Genet 2021 Sep 11. Epub 2021 Sep 11.

Department of Oncology and Molecular Medicine, Istituto Superiore di Sanità, 00161 Rome, Italy.

Germline activating mutations in HRAS cause Costello Syndrome (CS), a cancer prone multisystem disorder characterized by reduced postnatal growth. In CS, poor weight gain and growth are not caused by low caloric intake. Here we show that constitutive plasma membrane translocation and activation of the GLUT4 glucose transporter, via ROS-dependent AMPKα and p38 hyperactivation, occurs in CS, resulting in accelerated glycolysis, and increased fatty acid synthesis and storage as lipid droplets in primary fibroblasts. An accelerated autophagic flux was also identified as contributing to the increased energetic expenditure in CS. Concomitant inhibition of p38 and PI3K signaling by wortmannin was able to rescue both the dysregulated glucose intake and accelerated autophagic flux. Our findings provide a mechanistic link between upregulated HRAS function, defective growth and increased resting energetic expenditure in CS, and document that targeting p38 and PI3K signaling is able to revert this metabolic dysfunction.
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http://dx.doi.org/10.1093/hmg/ddab270DOI Listing
September 2021

Enlarged spinal nerve roots in RASopathies: Report of two cases.

Eur J Med Genet 2021 Apr 3;64(4):104187. Epub 2021 Mar 3.

Center for Rare Diseases and Birth Defects, Department of Woman and Child Health and Public Health, Fondazione Policlinico Universitario "A. Gemelli" IRCCS, Rome, Italy; Università Cattolica del Sacro Cuore, Rome, Italy.

RASopathies are a group of genetic conditions caused by germline variants in genes encoding signal transducers and modulators of the RAS-MAPK cascade. These disorders are multisystem diseases with considerable clinical overlap, even though distinct hallmarks are recognizable for each specific syndrome. Here we report on the presence of enlarged spinal nerve roots resembling neurofibromas, a typical neuroradiological finding of neurofibromatosis type 1, in two patients with a molecularly confirmed diagnosis of Noonan syndrome and cardio-facio-cutaneous syndrome, respectively. This evidence add enlarged spinal nerve roots as features shared among RASopathies. Future studies aiming to a better understanding of the molecular mechanisms leading to neurogenic tumor development in these patients are necessary to define their biological nature, evolution, prognosis and possible treatments.
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http://dx.doi.org/10.1016/j.ejmg.2021.104187DOI Listing
April 2021

Musculo-skeletal phenotype of Costello syndrome and cardio-facio-cutaneous syndrome: insights on the functional assessment status.

Orphanet J Rare Dis 2021 01 22;16(1):43. Epub 2021 Jan 22.

Center for Rare Diseases and Birth Defects, Department of Life Sciences and Public Health, Fondazione Policlinico Universitario A. Gemelli IRCCS, Largo Gemelli 8, 00168, Rome, Italy.

Background: Costello syndrome (CS) and cardio-facio-cutaneous syndrome (CFCS) belong to the RASopathies, a group of neurodevelopmental disorders with skeletal anomalies. Due to their rarity, the characterization of the musculo-skeletal phenotype in both disorders has been poorly characterized.

Patients And Methods: Herein we reported data on orthopedic findings and functional status of a large sample of CS and CFCS patients. Thirty-four patients (CS = 17 and CFCS = 17) were recruited. Functional and disability evaluations were performed by assessing the 6-min walking test (6MWT) and Pediatric Outcomes Data Collection Instrument (PODCI). Genotype/phenotype correlation was also provided.

Results: Orthopedic manifestations are highly prevalent in CS and CFCS and overlap in the two disorders. Overall, patients with CS harboring the recurrent HRAS Gly12Ser substitution show a more severe skeletal phenotype compared to patients carrying the Gly12Ala and Gly13Cys variants. Among CFCS patients, those with the MAP2K1/2 variant show different skeletal characteristics compared to BRAF variants, with a higher prevalence of orthopedic abnormalities. Functional assessment showed that patients with CS and CFCS reached lower values compared to the general population, with CFCS patients displaying the lowest scores.

Conclusions: Orthopedic manifestations appear universal features of CS and CFCS and they can evolve across patients' life. Longitudinal assessment of disability status by using 6MWT and PODCI could be useful to evaluate the functional impact of orthopedic manifestations on patients' outcome and help planning a tailored treatment of these comorbidities.
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http://dx.doi.org/10.1186/s13023-021-01674-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7821553PMC
January 2021

Compound heterozygosity for PTPN11 variants in a subject with Noonan syndrome provides insights into the mechanism of SHP2-related disorders.

Clin Genet 2021 03 4;99(3):457-461. Epub 2021 Jan 4.

Department of Oncology and Molecular Medicine, Istituto Superiore di Sanità, Rome, Italy.

The RASopathies are a family of clinically related disorders caused by mutations affecting genes participating in the RAS-MAPK signaling cascade. Among them, Noonan syndrome (NS) and Noonan syndrome with multiple lentigines (NSML) are allelic conditions principally associated with dominant mutations in PTPN11, which encodes the nonreceptor SH2 domain-containing protein tyrosine phosphatase SHP2. Individual PTPN11 mutations are specific to each syndrome and have opposite consequences on catalysis, but all favor SHP2's interaction with signaling partners. Here, we report on a subject with NS harboring biallelic variants in PTPN11. While the former (p.Leu261Phe) had previously been reported in NS, the latter (p.Thr357Met) is a novel change impairing catalysis. Members of the family carrying p.Thr357Met, however, did not show any obvious feature fitting NSML or within the RASopathy phenotypic spectrum. A major impact of this change on transcript processing and protein stability was excluded. These findings further support the view that NSML cannot be ascribed merely to impaired SHP2's catalytic activity and suggest that PTPN11 mutations causing this condition act through an alternative dominant mechanism.
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http://dx.doi.org/10.1111/cge.13904DOI Listing
March 2021

De Novo VPS4A Mutations Cause Multisystem Disease with Abnormal Neurodevelopment.

Am J Hum Genet 2020 12 12;107(6):1129-1148. Epub 2020 Nov 12.

Cambridge Institute for Medical Research, University of Cambridge, Cambridge CB2 0XY, UK; Department of Medical Genetics, University of Cambridge, Cambridge CB2 0QQ, UK. Electronic address:

The endosomal sorting complexes required for transport (ESCRTs) are essential for multiple membrane modeling and membrane-independent cellular processes. Here we describe six unrelated individuals with de novo missense variants affecting the ATPase domain of VPS4A, a critical enzyme regulating ESCRT function. Probands had structural brain abnormalities, severe neurodevelopmental delay, cataracts, growth impairment, and anemia. In cultured cells, overexpression of VPS4A mutants caused enlarged endosomal vacuoles resembling those induced by expression of known dominant-negative ATPase-defective forms of VPS4A. Proband-derived fibroblasts had enlarged endosomal structures with abnormal accumulation of the ESCRT protein IST1 on the limiting membrane. VPS4A function was also required for normal endosomal morphology and IST1 localization in iPSC-derived human neurons. Mutations affected other ESCRT-dependent cellular processes, including regulation of centrosome number, primary cilium morphology, nuclear membrane morphology, chromosome segregation, mitotic spindle formation, and cell cycle progression. We thus characterize a distinct multisystem disorder caused by mutations affecting VPS4A and demonstrate that its normal function is required for multiple human developmental and cellular processes.
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http://dx.doi.org/10.1016/j.ajhg.2020.10.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7820634PMC
December 2020

Enhanced MAPK1 Function Causes a Neurodevelopmental Disorder within the RASopathy Clinical Spectrum.

Am J Hum Genet 2020 09 27;107(3):499-513. Epub 2020 Jul 27.

Institute of Human Genetics, University Hospital Magdeburg, 39120 Magdeburg, Germany.

Signal transduction through the RAF-MEK-ERK pathway, the first described mitogen-associated protein kinase (MAPK) cascade, mediates multiple cellular processes and participates in early and late developmental programs. Aberrant signaling through this cascade contributes to oncogenesis and underlies the RASopathies, a family of cancer-prone disorders. Here, we report that de novo missense variants in MAPK1, encoding the mitogen-activated protein kinase 1 (i.e., extracellular signal-regulated protein kinase 2, ERK2), cause a neurodevelopmental disease within the RASopathy phenotypic spectrum, reminiscent of Noonan syndrome in some subjects. Pathogenic variants promote increased phosphorylation of the kinase, which enhances translocation to the nucleus and boosts MAPK signaling in vitro and in vivo. Two variant classes are identified, one of which directly disrupts binding to MKP3, a dual-specificity protein phosphatase negatively regulating ERK function. Importantly, signal dysregulation driven by pathogenic MAPK1 variants is stimulus reliant and retains dependence on MEK activity. Our data support a model in which the identified pathogenic variants operate with counteracting effects on MAPK1 function by differentially impacting the ability of the kinase to interact with regulators and substrates, which likely explains the minor role of these variants as driver events contributing to oncogenesis. After nearly 20 years from the discovery of the first gene implicated in Noonan syndrome, PTPN11, the last tier of the MAPK cascade joins the group of genes mutated in RASopathies.
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http://dx.doi.org/10.1016/j.ajhg.2020.06.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7477014PMC
September 2020

Pathogenic PTPN11 variants involving the poly-glutamine Gln -Gln -Gln stretch highlight the relevance of helix B in SHP2's functional regulation.

Hum Mutat 2020 06 11;41(6):1171-1182. Epub 2020 Mar 11.

Institute of Human Genetics, University Hospital of Magdeburg, Otto-von-Guericke-University, Magdeburg, Germany.

Germline PTPN11 mutations cause Noonan syndrome (NS), the most common disorder among RASopathies. PTPN11 encodes SHP2, a protein tyrosine-phosphatase controlling signaling through the RAS-MAPK and PI3K-AKT pathways. Generally, NS-causing PTPN11 mutations are missense changes destabilizing the inactive conformation of the protein or enhancing its binding to signaling partners. Here, we report on two PTPN11 variants resulting in the deletion or duplication of one of three adjacent glutamine residues (Gln -to-Gln ). While p.(Gln257dup) caused a typical NS phenotype in carriers of a first family, p.(Gln257del) had incomplete penetrance in a second family. Missense mutations involving Gln had previously been reported in NS. This poly-glutamine stretch is located on helix B of the PTP domain, a region involved in stabilizing SHP2 in its autoinhibited state. Molecular dynamics simulations predicted that changes affecting this motif perturb the SHP2's catalytically inactive conformation and/or substrate recognition. Biochemical data showed that duplication and deletion of Gln variably enhance SHP2's catalytic activity, while missense changes involving Gln affect substrate specificity. Expression of mutants in HEK293T cells documented their activating role on MAPK signaling, uncoupling catalytic activity and modulation of intracellular signaling. These findings further document the relevance of helix B in the regulation of SHP2's function.
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http://dx.doi.org/10.1002/humu.24007DOI Listing
June 2020

Frameshift mutations at the C-terminus of HIST1H1E result in a specific DNA hypomethylation signature.

Clin Epigenetics 2020 01 7;12(1). Epub 2020 Jan 7.

Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, IRCCS, 00146, Rome, Italy.

Background: We previously associated HIST1H1E mutations causing Rahman syndrome with a specific genome-wide methylation pattern.

Results: Methylome analysis from peripheral blood samples of six affected subjects led us to identify a specific hypomethylated profile. This "episignature" was enriched for genes involved in neuronal system development and function. A computational classifier yielded full sensitivity and specificity in detecting subjects with Rahman syndrome. Applying this model to a cohort of undiagnosed probands allowed us to reach diagnosis in one subject.

Conclusions: We demonstrate an epigenetic signature in subjects with Rahman syndrome that can be used to reach molecular diagnosis.
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http://dx.doi.org/10.1186/s13148-019-0804-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6947958PMC
January 2020

Aberrant Function of the C-Terminal Tail of HIST1H1E Accelerates Cellular Senescence and Causes Premature Aging.

Am J Hum Genet 2019 09 22;105(3):493-508. Epub 2019 Aug 22.

Department of Psychiatry, University of Pretoria, Weskoppies Hospital, Pretoria, 0001 South Africa.

Histones mediate dynamic packaging of nuclear DNA in chromatin, a process that is precisely controlled to guarantee efficient compaction of the genome and proper chromosomal segregation during cell division and to accomplish DNA replication, transcription, and repair. Due to the important structural and regulatory roles played by histones, it is not surprising that histone functional dysregulation or aberrant levels of histones can have severe consequences for multiple cellular processes and ultimately might affect development or contribute to cell transformation. Recently, germline frameshift mutations involving the C-terminal tail of HIST1H1E, which is a widely expressed member of the linker histone family and facilitates higher-order chromatin folding, have been causally linked to an as-yet poorly defined syndrome that includes intellectual disability. We report that these mutations result in stable proteins that reside in the nucleus, bind to chromatin, disrupt proper compaction of DNA, and are associated with a specific methylation pattern. Cells expressing these mutant proteins have a dramatically reduced proliferation rate and competence, hardly enter into the S phase, and undergo accelerated senescence. Remarkably, clinical assessment of a relatively large cohort of subjects sharing these mutations revealed a premature aging phenotype as a previously unrecognized feature of the disorder. Our findings identify a direct link between aberrant chromatin remodeling, cellular senescence, and accelerated aging.
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http://dx.doi.org/10.1016/j.ajhg.2019.07.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6731364PMC
September 2019

Activating Mutations of RRAS2 Are a Rare Cause of Noonan Syndrome.

Am J Hum Genet 2019 06 23;104(6):1223-1232. Epub 2019 May 23.

Département de Génétique, Assistance Publique des Hôpitaux de Paris (AP-HP) Hôpital Robert Debré, 75019 Paris, France; INSERM UMR 1141 - Université de Paris, 75019 Paris, France.

Aberrant signaling through pathways controlling cell response to extracellular stimuli constitutes a central theme in disorders affecting development. Signaling through RAS and the MAPK cascade controls a variety of cell decisions in response to cytokines, hormones, and growth factors, and its upregulation causes Noonan syndrome (NS), a developmental disorder whose major features include a distinctive facies, a wide spectrum of cardiac defects, short stature, variable cognitive impairment, and predisposition to malignancies. NS is genetically heterogeneous, and mutations in more than ten genes have been reported to underlie this disorder. Despite the large number of genes implicated, about 10%-20% of affected individuals with a clinical diagnosis of NS do not have mutations in known RASopathy-associated genes, indicating that additional unidentified genes contribute to the disease, when mutated. By using a mixed strategy of functional candidacy and exome sequencing, we identify RRAS2 as a gene implicated in NS in six unrelated subjects/families. We show that the NS-causing RRAS2 variants affect highly conserved residues localized around the nucleotide binding pocket of the GTPase and are predicted to variably affect diverse aspects of RRAS2 biochemical behavior, including nucleotide binding, GTP hydrolysis, and interaction with effectors. Additionally, all pathogenic variants increase activation of the MAPK cascade and variably impact cell morphology and cytoskeletal rearrangement. Finally, we provide a characterization of the clinical phenotype associated with RRAS2 mutations.
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http://dx.doi.org/10.1016/j.ajhg.2019.04.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6562003PMC
June 2019

Organoids as a new model for improving regenerative medicine and cancer personalized therapy in renal diseases.

Cell Death Dis 2019 02 27;10(3):201. Epub 2019 Feb 27.

IRCCS, Regina Elena National Cancer Institute, Rome, Italy.

The pressure towards innovation and creation of new model systems in regenerative medicine and cancer research has fostered the development of novel potential therapeutic applications. Kidney injuries provoke a high request of organ transplants making it the most demanding system in the field of regenerative medicine. Furthermore, renal cancer frequently threaten patients' life and aggressive forms still remain difficult to treat. Ethical issues related to the use of embryonic stem cells, has fueled research on adult, patient-specific pluripotent stem cells as a model for discovery and therapeutic development, but to date, normal and cancerous renal experimental models are lacking. Several research groups are focusing on the development of organoid cultures. Since organoids mimic the original tissue architecture in vitro, they represent an excellent model for tissue engineering studies and cancer therapy testing. We established normal and tumor renal cell carcinoma organoids previously maintained in a heterogeneous multi-clone stem cell-like enriching medium. Starting from adult normal kidney specimens, we were able to isolate and propagate organoid 3D-structures composed of both differentiated and undifferentiated cells while expressing nephron specific markers. Furthermore, we were capable to establish organoids derived from cancer tissues although with a success rate inferior to that of their normal counterpart. Cancer cultures displayed epithelial and mesenchymal phenotype while retaining tumor specific markers. Of note, tumor organoids recapitulated neoplastic masses when orthotopically injected into immunocompromised mice. Our data suggest an innovative approach of long-term establishment of normal- and cancer-derived renal organoids obtained from cultures of fleshly dissociated adult tissues. Our results pave the way to organ replacement pioneering strategies as well as to new models for studying drug-induced nephrotoxicity and renal diseases. Along similar lines, deriving organoids from renal cancer patients opens unprecedented opportunities for generation of preclinical models aimed at improving therapeutic treatments.
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http://dx.doi.org/10.1038/s41419-019-1453-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6393468PMC
February 2019

Biallelic mutations in early-onset, variably progressive neurodegeneration.

Neurology 2018 07 29;91(4):e319-e330. Epub 2018 Jun 29.

From the Genetics and Rare Diseases Research Division (V.M., G.C., T.R., M.D.N., A.C., F.P., R.C., M.T.), Ospedale Pediatrico Bambino Gesù; Department of Oncology and Molecular Medicine (E.F., S.M.) and Confocal Microscopy Unit (S.C.), Core Facilities, Istituto Superiore di Sanità, Rome, Italy; Center for Human Disease Modeling (Z.K., M.M.K., N.K.), Duke University School of Medicine, Durham, NC; Institutes of Neurology (G.P., S.S.) and Nuclear Medicine (D.D.G.), Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario A. Gemelli, Rome, Italy; Department of Genetics (H.G., N.M.), Faculty of Science, Shahid Chamran University of Ahvaz; Narges Medical Genetics and Prenatal Diagnosis Laboratory (H.G., N.M., A. Sedaghat, J.Z., G.R.S.), Kianpars, Ahvaz; Research and Clinical Center for Infertility (M.D.), Yazd Reproductive Sciences Institute, Medical Genetics Research Centre (M.D., M.Y.V.M.), and Department of Medical Genetics (M.Y.V.M.), Shahid Sadoughi University of Medical Sciences, Yazd, Iran; Department of Experimental Medicine (A.T., V.C.), Università "Sapienza," Rome, Italy; Genetics and Molecular Cell Sciences Research Centre (Y.J., R.M.), St. George's University of London, UK; Department of Paediatric Neurology (R.A.M.), Golestan Medical, Educational, and Research Center, and Department of Medical Genetics (G.R.S.), Faculty of Medicine, Ahvaz Jundishapur University of Medical Sciences, Iran; University of Exeter Medical School (A.R.J.), RILD, Royal Devon & Exeter Hospital, UK; and Department of Neurology (A. Sherafat), Kerman University of Medical Sciences, Iran.

Objective: To characterize clinically and molecularly an early-onset, variably progressive neurodegenerative disorder characterized by a cerebellar syndrome with severe ataxia, gaze palsy, dyskinesia, dystonia, and cognitive decline affecting 11 individuals from 3 consanguineous families.

Methods: We used whole-exome sequencing (WES) (families 1 and 2) and a combined approach based on homozygosity mapping and WES (family 3). We performed in vitro studies to explore the effect of the nontruncating mutation on protein function and the effect of impaired SQSTM1 function on autophagy. We analyzed the consequences of sqstm1 down-modulation on the structural integrity of the cerebellum in vivo using zebrafish as a model.

Results: We identified 3 homozygous inactivating variants, including a splice site substitution (c.301+2T>A) causing aberrant transcript processing and accelerated degradation of a resulting protein lacking exon 2, as well as 2 truncating changes (c.875_876insT and c.934_936delinsTGA). We show that loss of SQSTM1 causes impaired production of ubiquitin-positive protein aggregates in response to misfolded protein stress and decelerated autophagic flux. The consequences of sqstm1 down-modulation on the structural integrity of the cerebellum in zebrafish documented a variable but reproducible phenotype characterized by cerebellum anomalies ranging from depletion of axonal connections to complete atrophy. We provide a detailed clinical characterization of the disorder; the natural history is reported for 2 siblings who have been followed up for >20 years.

Conclusions: This study offers an accurate clinical characterization of this recently recognized neurodegenerative disorder caused by biallelic inactivating mutations in and links this phenotype to defective selective autophagy.
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http://dx.doi.org/10.1212/WNL.0000000000005869DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6070386PMC
July 2018

Genotype and phenotype spectrum of NRAS germline variants.

Eur J Hum Genet 2017 06 3;25(7):823-831. Epub 2017 May 3.

Institute of Human Genetics, University Hospital Magdeburg, Magdeburg, Germany.

RASopathies comprise a group of disorders clinically characterized by short stature, heart defects, facial dysmorphism, and varying degrees of intellectual disability and cancer predisposition. They are caused by germline variants in genes encoding key components or modulators of the highly conserved RAS-MAPK signalling pathway that lead to dysregulation of cell signal transmission. Germline changes in the genes encoding members of the RAS subfamily of GTPases are rare and associated with variable phenotypes of the RASopathy spectrum, ranging from Costello syndrome (HRAS variants) to Noonan and Cardiofaciocutaneous syndromes (KRAS variants). A small number of RASopathy cases with disease-causing germline NRAS alterations have been reported. Affected individuals exhibited features fitting Noonan syndrome, and the observed germline variants differed from the typical oncogenic NRAS changes occurring as somatic events in tumours. Here we describe 19 new cases with RASopathy due to disease-causing variants in NRAS. Importantly, four of them harbored missense changes affecting Gly12, which was previously described to occur exclusively in cancer. The phenotype in our cohort was variable but well within the RASopathy spectrum. Further, one of the patients (c.35G>A; p.(Gly12Asp)) had a myeloproliferative disorder, and one subject (c.34G>C; p.(Gly12Arg)) exhibited an uncharacterized brain tumour. With this report, we expand the genotype and phenotype spectrum of RASopathy-associated germline NRAS variants and provide evidence that NRAS variants do not spare the cancer-associated mutation hotspots.
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http://dx.doi.org/10.1038/ejhg.2017.65DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5520077PMC
June 2017

Aberrant HRAS transcript processing underlies a distinctive phenotype within the RASopathy clinical spectrum.

Hum Mutat 2017 07 3;38(7):798-804. Epub 2017 May 3.

Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, Rome, Italy.

RASopathies are a group of rare, clinically related conditions affecting development and growth, and are caused by germline mutations in genes encoding signal transducers and modulators with a role in the RAS signaling network. These disorders share facial dysmorphia, short stature, variable cognitive deficits, skeletal and cardiac defects, and a variable predisposition to malignancies. Here, we report on a de novo 10-nucleotide-long deletion in HRAS (c.481_490delGGGACCCTCT, NM_176795.4; p.Leu163ProfsTer52, NP_789765.1) affecting transcript processing as a novel event underlying a RASopathy characterized by developmental delay, intellectual disability and autistic features, distinctive coarse facies, reduced growth, and ectodermal anomalies. Molecular and biochemical studies demonstrated that the deletion promotes constitutive retention of exon IDX, which is generally skipped during HRAS transcript processing, and results in a stable and mildly hyperactive GDP/GTP-bound protein that is constitutively targeted to the plasma membrane. Our findings document a new mechanism leading to altered HRAS function that underlies a previously unappreciated phenotype within the RASopathy spectrum.
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http://dx.doi.org/10.1002/humu.23224DOI Listing
July 2017

Structural, Functional, and Clinical Characterization of a Novel PTPN11 Mutation Cluster Underlying Noonan Syndrome.

Hum Mutat 2017 04 7;38(4):451-459. Epub 2017 Feb 7.

Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, IRCCS, Rome, Italy.

Germline mutations in PTPN11, the gene encoding the Src-homology 2 (SH2) domain-containing protein tyrosine phosphatase (SHP2), cause Noonan syndrome (NS), a relatively common, clinically variable, multisystem disorder. Here, we report on the identification of five different PTPN11 missense changes affecting residues Leu , Leu , and Arg in 16 unrelated individuals with clinical diagnosis of NS or with features suggestive for this disorder, specifying a novel disease-causing mutation cluster. Expression of the mutant proteins in HEK293T cells documented their activating role on MAPK signaling. Structural data predicted a gain-of-function role of substitutions at residues Leu and Arg exerted by disruption of the N-SH2/PTP autoinhibitory interaction. Molecular dynamics simulations suggested a more complex behavior for changes affecting Leu , with possible impact on SHP2's catalytic activity/selectivity and proper interaction of the PTP domain with the regulatory SH2 domains. Consistent with that, biochemical data indicated that substitutions at codons 262 and 265 increased the catalytic activity of the phosphatase, while those affecting codon 261 were only moderately activating but impacted substrate specificity. Remarkably, these mutations underlie a relatively mild form of NS characterized by low prevalence of cardiac defects, short stature, and cognitive and behavioral issues, as well as less evident typical facial features.
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http://dx.doi.org/10.1002/humu.23175DOI Listing
April 2017

Biallelic Mutations in TBCD, Encoding the Tubulin Folding Cofactor D, Perturb Microtubule Dynamics and Cause Early-Onset Encephalopathy.

Am J Hum Genet 2016 Oct 22;99(4):962-973. Epub 2016 Sep 22.

Department of Human Genetics, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen 1105, the Netherlands.

Microtubules are dynamic cytoskeletal elements coordinating and supporting a variety of neuronal processes, including cell division, migration, polarity, intracellular trafficking, and signal transduction. Mutations in genes encoding tubulins and microtubule-associated proteins are known to cause neurodevelopmental and neurodegenerative disorders. Growing evidence suggests that altered microtubule dynamics may also underlie or contribute to neurodevelopmental disorders and neurodegeneration. We report that biallelic mutations in TBCD, encoding one of the five co-chaperones required for assembly and disassembly of the αβ-tubulin heterodimer, the structural unit of microtubules, cause a disease with neurodevelopmental and neurodegenerative features characterized by early-onset cortical atrophy, secondary hypomyelination, microcephaly, thin corpus callosum, developmental delay, intellectual disability, seizures, optic atrophy, and spastic quadriplegia. Molecular dynamics simulations predicted long-range and/or local structural perturbations associated with the disease-causing mutations. Biochemical analyses documented variably reduced levels of TBCD, indicating relative instability of mutant proteins, and defective β-tubulin binding in a subset of the tested mutants. Reduced or defective TBCD function resulted in decreased soluble α/β-tubulin levels and accelerated microtubule polymerization in fibroblasts from affected subjects, demonstrating an overall shift toward a more rapidly growing and stable microtubule population. These cells displayed an aberrant mitotic spindle with disorganized, tangle-shaped microtubules and reduced aster formation, which however did not alter appreciably the rate of cell proliferation. Our findings establish that defective TBCD function underlies a recognizable encephalopathy and drives accelerated microtubule polymerization and enhanced microtubule stability, underscoring an additional cause of altered microtubule dynamics with impact on neuronal function and survival in the developing brain.
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http://dx.doi.org/10.1016/j.ajhg.2016.08.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5065658PMC
October 2016

TBCE Mutations Cause Early-Onset Progressive Encephalopathy with Distal Spinal Muscular Atrophy.

Am J Hum Genet 2016 Oct 22;99(4):974-983. Epub 2016 Sep 22.

Genetics and Rare Diseases Research Division, Ospedale Pediatrico Bambino Gesù, 00146 Rome, Italy. Electronic address:

Tubulinopathies constitute a family of neurodevelopmental/neurodegenerative disorders caused by mutations in several genes encoding tubulin isoforms. Loss-of-function mutations in TBCE, encoding one of the five tubulin-specific chaperones involved in tubulin folding and polymerization, cause two rare neurodevelopmental syndromes, hypoparathyroidism-retardation-dysmorphism and Kenny-Caffey syndrome. Although a missense mutation in Tbce has been associated with progressive distal motor neuronopathy in the pmn/pmn mice, no similar degenerative phenotype has been recognized in humans. We report on the identification of an early-onset and progressive neurodegenerative encephalopathy with distal spinal muscular atrophy resembling the phenotype of pmn/pmn mice and caused by biallelic TBCE mutations, with the c.464T>A (p.Ile155Asn) change occurring at the heterozygous/homozygous state in six affected subjects from four unrelated families originated from the same geographical area in Southern Italy. Western blot analysis of patient fibroblasts documented a reduced amount of TBCE, suggestive of rapid degradation of the mutant protein, similarly to what was observed in pmn/pmn fibroblasts. The impact of TBCE mutations on microtubule polymerization was determined using biochemical fractionation and analyzing the nucleation and growth of microtubules at the centrosome and extracentrosomal sites after treatment with nocodazole. Primary fibroblasts obtained from affected subjects displayed a reduced level of polymerized α-tubulin, similarly to tail fibroblasts of pmn/pmn mice. Moreover, markedly delayed microtubule re-polymerization and abnormal mitotic spindles with disorganized microtubule arrangement were also documented. Although loss of function of TBCE has been documented to impact multiple developmental processes, the present findings provide evidence that hypomorphic TBCE mutations primarily drive neurodegeneration.
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http://dx.doi.org/10.1016/j.ajhg.2016.08.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5065657PMC
October 2016

Myeloid Dysregulation in a Human Induced Pluripotent Stem Cell Model of PTPN11-Associated Juvenile Myelomonocytic Leukemia.

Cell Rep 2015 Oct 8;13(3):504-515. Epub 2015 Oct 8.

The Mindich Child Health and Development Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA; Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA. Electronic address:

Somatic PTPN11 mutations cause juvenile myelomonocytic leukemia (JMML). Germline PTPN11 defects cause Noonan syndrome (NS), and specific inherited mutations cause NS/JMML. Here, we report that hematopoietic cells differentiated from human induced pluripotent stem cells (hiPSCs) harboring NS/JMML-causing PTPN11 mutations recapitulated JMML features. hiPSC-derived NS/JMML myeloid cells exhibited increased signaling through STAT5 and upregulation of miR-223 and miR-15a. Similarly, miR-223 and miR-15a were upregulated in 11/19 JMML bone marrow mononuclear cells harboring PTPN11 mutations, but not those without PTPN11 defects. Reducing miR-223's function in NS/JMML hiPSCs normalized myelogenesis. MicroRNA target gene expression levels were reduced in hiPSC-derived myeloid cells as well as in JMML cells with PTPN11 mutations. Thus, studying an inherited human cancer syndrome with hiPSCs illuminated early oncogenesis prior to the accumulation of secondary genomic alterations, enabling us to discover microRNA dysregulation, establishing a genotype-phenotype association for JMML and providing therapeutic targets.
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http://dx.doi.org/10.1016/j.celrep.2015.09.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4618050PMC
October 2015

Distinct Acute Lymphoblastic Leukemia (ALL)-associated Janus Kinase 3 (JAK3) Mutants Exhibit Different Cytokine-Receptor Requirements and JAK Inhibitor Specificities.

J Biol Chem 2015 Nov 7;290(48):29022-34. Epub 2015 Oct 7.

From the Ludwig Institute for Cancer Research, Brussels Branch and the de Duve Institute, Université Catholique de Louvain, 1200 Brussels, Belgium, the Hematology Unit, Cliniques Universitaires Saint-Luc, 1200 Brussels, Belgium, and

JAK1 and JAK3 are recurrently mutated in acute lymphoblastic leukemia. These tyrosine kinases associate with heterodimeric cytokine receptors such as IL-7 receptor or IL-9 receptor, in which JAK1 is appended to the specific chain, and JAK3 is appended to the common gamma chain. Here, we studied the role of these receptor complexes in mediating the oncogenic activity of JAK3 mutants. Although JAK3(V674A) and the majority of other JAK3 mutants needed to bind to a functional cytokine receptor complex to constitutively activate STAT5, JAK3(L857P) was unexpectedly found to not depend on such receptor complexes for its activity, which was induced without receptor or JAK1 co-expression. Introducing a mutation in the FERM domain that abolished JAK-receptor interaction did not affect JAK3(L857P) activity, whereas it inhibited the other receptor-dependent mutants. The same cytokine receptor independence as for JAK3(L857P) was observed for homologous Leu(857) mutations of JAK1 and JAK2 and for JAK3(L875H). This different cytokine receptor requirement correlated with different functional properties in vivo and with distinct sensitivity to JAK inhibitors. Transduction of murine hematopoietic cells with JAK3(V674A) led homogenously to lymphoblastic leukemias in BALB/c mice. In contrast, transduction with JAK3(L857P) induced various types of lymphoid and myeloid leukemias. Moreover, ruxolitinib, which preferentially blocks JAK1 and JAK2, abolished the proliferation of cells transformed by the receptor-dependent JAK3(V674A), yet proved much less potent on cells expressing JAK3(L857P). These particular cells were, in contrast, more sensitive to JAK3-specific inhibitors. Altogether, our results showed that different JAK3 mutations induce constitutive activation through distinct mechanisms, pointing to specific therapeutic perspectives.
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http://dx.doi.org/10.1074/jbc.M115.670224DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4661414PMC
November 2015

Mutations in KCNH1 and ATP6V1B2 cause Zimmermann-Laband syndrome.

Nat Genet 2015 Jun 27;47(6):661-7. Epub 2015 Apr 27.

Institute of Human Genetics, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.

Zimmermann-Laband syndrome (ZLS) is a developmental disorder characterized by facial dysmorphism with gingival enlargement, intellectual disability, hypoplasia or aplasia of nails and terminal phalanges, and hypertrichosis. We report that heterozygous missense mutations in KCNH1 account for a considerable proportion of ZLS. KCNH1 encodes the voltage-gated K(+) channel Eag1 (Kv10.1). Patch-clamp recordings showed strong negative shifts in voltage-dependent activation for all but one KCNH1 channel mutant (Gly469Arg). Coexpression of Gly469Arg with wild-type KCNH1 resulted in heterotetrameric channels with reduced conductance at positive potentials but pronounced conductance at negative potentials. These data support a gain-of-function effect for all ZLS-associated KCNH1 mutants. We also identified a recurrent de novo missense change in ATP6V1B2, encoding the B2 subunit of the multimeric vacuolar H(+) ATPase, in two individuals with ZLS. Structural analysis predicts a perturbing effect of the mutation on complex assembly. Our findings demonstrate that KCNH1 mutations cause ZLS and document genetic heterogeneity for this disorder.
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http://dx.doi.org/10.1038/ng.3282DOI Listing
June 2015

Cooperating JAK1 and JAK3 mutants increase resistance to JAK inhibitors.

Blood 2014 Dec 28;124(26):3924-31. Epub 2014 Oct 28.

Ludwig Institute for Cancer Research, Brussels Branch, Belgium; de Duve Institute, Université Catholique de Louvain, Brussels, Belgium;

The acquisition of growth signal self-sufficiency is 1 of the hallmarks of cancer. We previously reported that the murine interleukin-9-dependent TS1 cell line gives rise to growth factor-independent clones with constitutive activation of the Janus kinase (JAK)- signal transducer and activator of transcription (STAT) pathway. Here, we show that this transforming event results from activating mutations either in JAK1, JAK3, or in both kinases. Transient and stable expression of JAK1 and/or JAK3 mutants showed that each mutant induces STAT activation and that their coexpression further increases this activation. The proliferation of growth factor-independent TS1 clones can be efficiently blocked by JAK inhibitors such as ruxolitinib or CMP6 in short-term assays. However, resistant clones occur upon long-term culture in the presence of inhibitors. Surprisingly, resistance to CMP6 was not caused by the acquisition of secondary mutations in the adenosine triphosphate-binding pocket of the JAK mutant. Indeed, cells that originally showed a JAK1-activating mutation became resistant to inhibitors by acquiring another activating mutation in JAK3, whereas cells that originally showed a JAK3-activating mutation became resistant to inhibitors by acquiring another activating mutation in JAK1. These observations underline the cooperation between JAK1 and JAK3 mutants in T-cell transformation and represent a new mechanism of acquisition of resistance against JAK inhibitors.
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http://dx.doi.org/10.1182/blood-2014-05-576652DOI Listing
December 2014

RAF1 mutations in childhood-onset dilated cardiomyopathy.

Nat Genet 2014 Jun 28;46(6):635-639. Epub 2014 Apr 28.

Department of Pediatrics, Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, USA.

Dilated cardiomyopathy (DCM) is a highly heterogeneous trait with sarcomeric gene mutations predominating. The cause of a substantial percentage of DCMs remains unknown, and no gene-specific therapy is available. On the basis of resequencing of 513 DCM cases and 1,150 matched controls from various cohorts of distinct ancestry, we discovered rare, functional RAF1 mutations in 3 of the cohorts (South Indian, North Indian and Japanese). The prevalence of RAF1 mutations was ~9% in childhood-onset DCM cases in these three cohorts. Biochemical studies showed that DCM-associated RAF1 mutants had altered kinase activity, resulting in largely unaltered ERK activation but in AKT that was hyperactivated in a BRAF-dependent manner. Constitutive expression of these mutants in zebrafish embryos resulted in a heart failure phenotype with AKT hyperactivation that was rescued by treatment with rapamycin. These findings provide new mechanistic insights and potential therapeutic targets for RAF1-associated DCM and further expand the clinical spectrum of RAF1-related human disorders.
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http://dx.doi.org/10.1038/ng.2963DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4049514PMC
June 2014

Activating mutations in RRAS underlie a phenotype within the RASopathy spectrum and contribute to leukaemogenesis.

Hum Mol Genet 2014 Aug 4;23(16):4315-27. Epub 2014 Apr 4.

Genetica Clinica Pediatrica, Clinica Pediatrica Università Milano Bicocca, Fondazione MBBM, A.O. S. Gerardo, Monza 20900, Italy.

RASopathies, a family of disorders characterized by cardiac defects, defective growth, facial dysmorphism, variable cognitive deficits and predisposition to certain malignancies, are caused by constitutional dysregulation of RAS signalling predominantly through the RAF/MEK/ERK (MAPK) cascade. We report on two germline mutations (p.Gly39dup and p.Val55Met) in RRAS, a gene encoding a small monomeric GTPase controlling cell adhesion, spreading and migration, underlying a rare (2 subjects among 504 individuals analysed) and variable phenotype with features partially overlapping Noonan syndrome, the most common RASopathy. We also identified somatic RRAS mutations (p.Gly39dup and p.Gln87Leu) in 2 of 110 cases of non-syndromic juvenile myelomonocytic leukaemia, a childhood myeloproliferative/myelodysplastic disease caused by upregulated RAS signalling, defining an atypical form of this haematological disorder rapidly progressing to acute myeloid leukaemia. Two of the three identified mutations affected known oncogenic hotspots of RAS genes and conferred variably enhanced RRAS function and stimulus-dependent MAPK activation. Expression of an RRAS mutant homolog in Caenorhabditis elegans enhanced RAS signalling and engendered protruding vulva, a phenotype previously linked to the RASopathy-causing SHOC2(S2G) mutant. Overall, these findings provide evidence of a functional link between RRAS and MAPK signalling and reveal an unpredicted role of enhanced RRAS function in human disease.
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http://dx.doi.org/10.1093/hmg/ddu148DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4103678PMC
August 2014

Loss of function of the E3 ubiquitin-protein ligase UBE3B causes Kaufman oculocerebrofacial syndrome.

J Med Genet 2013 Aug 17;50(8):493-9. Epub 2013 May 17.

Dipartimento di Ematologia, Oncologia e Medicina Molecolare, Istituto Superioredi Sanità, Rome, Italy.

Background: Kaufman oculocerebrofacial syndrome (KOS) is a developmental disorder characterised by reduced growth, microcephaly, ocular anomalies (microcornea, strabismus, myopia, and pale optic disk), distinctive facial features (narrow palpebral fissures, telecanthus, sparse and laterally broad eyebrows, preauricular tags, and micrognathia), mental retardation, and generalised hypotonia. KOS is a rare, possibly underestimated condition, with fewer than 10 cases reported to date. Here we investigate the molecular cause underlying KOS.

Methods: An exome sequencing approach was used on a single affected individual of an Italian consanguineous family coupled with mutation scanning using Sanger sequencing on a second unrelated subject with clinical features fitting the disorder.

Results: Exome sequencing was able to identify homozygosity for a novel truncating mutation (c.556C>T, p.Arg186stop) in UBE3B, which encodes a widely expressed HECT (homologous to the E6-AP carboxyl terminus) domain E3 ubiquitin-protein ligase. Homozygosity for a different nonsense lesion affecting the gene (c.1166G>A, p.Trp389stop) was documented in the second affected subject, supporting the recessive mode of inheritance of the disorder. Mutation scanning of the entire UBE3B coding sequence on a selected cohort of subjects with features overlapping, in part, those recurring in KOS did not reveal disease-causing mutations, suggesting phenotypic homogeneity of UBE3B lesions.

Discussion: Our data provide evidence that KOS is caused by UBE3B loss of function, and further demonstrate the impact of misregulation of protein ubiquitination on development and growth. The available clinical records, including those referring to four UBE3B mutation-positive subjects recently described as belonging to a previously unreported entity, which fits KOS, document the clinical homogeneity of this disorder.
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http://dx.doi.org/10.1136/jmedgenet-2012-101405DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3717725PMC
August 2013

Progressive extreme heterotopic calcification.

Am J Med Genet A 2013 Jul 17;161A(7):1706-13. Epub 2013 May 17.

Dipartimento di Scienze della Sanità Pubblica e Pediatriche, Università di Torino, Torino, Italy.

The formation of ectopic calcifications in soft tissues can occur either sporadically or as a genetically determined condition, and is seen only infrequently. We report on a girl in whom widespread, rapidly progressive ectopic calcifications were detected shortly after birth. Calcifications became present around all joints, tendons and ligaments, but did not involve internal organs and skin, and eventually caused almost complete immobility of the child at 2 years. There were no other health problems and cognitive development was normal. We compare the manifestations in the child to the characteristics of known entities causing ectopic calcifications and conclude the child differs to each. Laboratory evaluation failed to identify autoimmune phenomena as well as calcium metabolism or other biochemical abnormalities; molecular studies did not identify occurrence of mutations in disease genes known to be involved in ectopic calcifications. We conclude the manifestations in the child represent an unreported entity of hitherto unknown etiology.
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http://dx.doi.org/10.1002/ajmg.a.35944DOI Listing
July 2013

Counteracting effects operating on Src homology 2 domain-containing protein-tyrosine phosphatase 2 (SHP2) function drive selection of the recurrent Y62D and Y63C substitutions in Noonan syndrome.

J Biol Chem 2012 Aug 18;287(32):27066-77. Epub 2012 Jun 18.

Dipartimento di Ematologia, Oncologia e Medicina Molecolare, Istituto Superiore di Sanità, 00161 Rome, Italy.

Activating mutations in PTPN11 cause Noonan syndrome, the most common nonchromosomal disorder affecting development and growth. PTPN11 encodes SHP2, an Src homology 2 (SH2) domain-containing protein-tyrosine phosphatase that positively modulates RAS function. Here, we characterized functionally all possible amino acid substitutions arising from single-base changes affecting codons 62 and 63 to explore the molecular mechanisms lying behind the largely invariant occurrence of the Y62D and Y63C substitutions recurring in Noonan syndrome. We provide structural and biochemical data indicating that the autoinhibitory interaction between the N-SH2 and protein-tyrosine phosphatase (PTP) domains is perturbed in both mutants as a result of an extensive structural rearrangement of the N-SH2 domain. Most mutations affecting Tyr(63) exerted an unpredicted disrupting effect on the structure of the N-SH2 phosphopeptide-binding cleft mediating the interaction of SHP2 with signaling partners. Among all the amino acid changes affecting that codon, the disease-causing mutation was the only substitution that perturbed the stability of the inactive conformation of SHP2 without severely impairing proper phosphopeptide binding of N-SH2. On the other hand, the disruptive effect of the Y62D change on the autoinhibited conformation of the protein was balanced, in part, by less efficient binding properties of the mutant. Overall, our data demonstrate that the selection-by-function mechanism acting as driving force for PTPN11 mutations affecting codons 62 and 63 implies balancing of counteracting effects operating on the allosteric control of the function of SHP2.
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http://dx.doi.org/10.1074/jbc.M112.350231DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3411048PMC
August 2012

Transcriptional hallmarks of Noonan syndrome and Noonan-like syndrome with loose anagen hair.

Hum Mutat 2012 Apr 14;33(4):703-9. Epub 2012 Feb 14.

Department of Pediatrics, University of Torino Medical School, Torino, Italy.

Noonan syndrome (NS) is among the most common nonchromosomal disorders affecting development and growth. NS is genetically heterogeneous, being caused by germline mutations affecting various genes implicated in the RAS signaling network. This network transduces extracellular signals into intracellular biochemical and transcriptional responses controlling cell proliferation, differentiation, metabolism, and senescence. To explore the transcriptional consequences of NS-causing mutations, we performed global mRNA expression profiling on peripheral blood mononuclear cells obtained from 23 NS patients carrying heterozygous mutations in PTPN11 or SOS1. Gene expression profiling was also resolved in five subjects with Noonan-like syndrome with loose anagen hair (NS/LAH), a condition clinically related to NS and caused by an invariant mutation in SHOC2. Robust transcriptional signatures were found to specifically discriminate each of the three mutation groups from 21 age- and sex-matched controls. Despite the only partial overlap in terms of gene composition, the three signatures showed a notable concordance in terms of biological processes and regulatory circuits affected. These data establish expression profiling of peripheral blood mononuclear cells as a powerful tool to appreciate differential perturbations driven by germline mutations of transducers involved in RAS signaling and to dissect molecular mechanisms underlying NS and other RASopathies.
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http://dx.doi.org/10.1002/humu.22026DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3332054PMC
April 2012

Mutation of SHOC2 promotes aberrant protein N-myristoylation and causes Noonan-like syndrome with loose anagen hair.

Nat Genet 2009 Sep 16;41(9):1022-6. Epub 2009 Aug 16.

Dipartimento di Ematologia, Oncologia e Medicina Molecolare, Istituto Superiore di Sanità, Rome, Italy.

N-myristoylation is a common form of co-translational protein fatty acylation resulting from the attachment of myristate to a required N-terminal glycine residue. We show that aberrantly acquired N-myristoylation of SHOC2, a leucine-rich repeat-containing protein that positively modulates RAS-MAPK signal flow, underlies a clinically distinctive condition of the neuro-cardio-facial-cutaneous disorders family. Twenty-five subjects with a relatively consistent phenotype previously termed Noonan-like syndrome with loose anagen hair (MIM607721) shared the 4A>G missense change in SHOC2 (producing an S2G amino acid substitution) that introduces an N-myristoylation site, resulting in aberrant targeting of SHOC2 to the plasma membrane and impaired translocation to the nucleus upon growth factor stimulation. Expression of SHOC2(S2G) in vitro enhanced MAPK activation in a cell type-specific fashion. Induction of SHOC2(S2G) in Caenorhabditis elegans engendered protruding vulva, a neomorphic phenotype previously associated with aberrant signaling. These results document the first example of an acquired N-terminal lipid modification of a protein causing human disease.
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http://dx.doi.org/10.1038/ng.425DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2765465PMC
September 2009
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