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      Defining RASopathy

      review-article
      1 , 2 , *
      Disease Models & Mechanisms
      The Company of Biologists Ltd

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          ABSTRACT

          The term RASopathy was originally created to describe a phenotypically similar group of medical genetic syndromes caused by germline pathogenic variants in components of the RAS/mitogen-activated protein kinase (RAS/MAPK) pathway. In defining a RASopathy syndrome, one needs to consider the complex nature of the RAS/MAPK pathway, the numerous genes and regulatory components involved, its crosstalk with other signaling pathways and the phenotypic spectrum among these syndromes. Three main guiding principles to the definition should be considered. First, a RASopathy is a clinical syndrome with overlapping phenotypic features caused by germline pathogenic variants associated with the RAS/MAPK pathway. Second, a RASopathy is caused by multiple pathogenetic mechanisms, all of which lead to a similar outcome of RAS/MAPK pathway activation/dysregulation. Finally, because a RASopathy has dysfunctional germline RAS/MAPK pathway activation/dysregulation, it may, therefore, be amenable to treatment with pathway modulators.

          Abstract

          Summary: RASopathy is a term used to unify a phenotypically similar group of medical genetic syndromes, yet its definition is challenging and should consider the perspectives of clinicians, scientists and the patients.

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          Most cited references33

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          RAS Proteins and Their Regulators in Human Disease.

          RAS proteins are binary switches, cycling between ON and OFF states during signal transduction. These switches are normally tightly controlled, but in RAS-related diseases, such as cancer, RASopathies, and many psychiatric disorders, mutations in the RAS genes or their regulators render RAS proteins persistently active. The structural basis of the switch and many of the pathways that RAS controls are well known, but the precise mechanisms by which RAS proteins function are less clear. All RAS biology occurs in membranes: a precise understanding of RAS' interaction with membranes is essential to understand RAS action and to intervene in RAS-driven diseases.
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            The RASopathies.

            The RASopathies are a clinically defined group of medical genetic syndromes caused by germline mutations in genes that encode components or regulators of the Ras/mitogen-activated protein kinase (MAPK) pathway. These disorders include neurofibromatosis type 1, Noonan syndrome, Noonan syndrome with multiple lentigines, capillary malformation-arteriovenous malformation syndrome, Costello syndrome, cardio-facio-cutaneous syndrome, and Legius syndrome. Because of the common underlying Ras/MAPK pathway dysregulation, the RASopathies exhibit numerous overlapping phenotypic features. The Ras/MAPK pathway plays an essential role in regulating the cell cycle and cellular growth, differentiation, and senescence, all of which are critical to normal development. Therefore, it is not surprising that Ras/MAPK pathway dysregulation has profound deleterious effects on both embryonic and later stages of development. The Ras/MAPK pathway has been well studied in cancer and is an attractive target for small-molecule inhibition to treat various malignancies. The use of these molecules to ameliorate developmental defects in the RASopathies is under consideration.
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              Activity of Selumetinib in Neurofibromatosis Type 1-Related Plexiform Neurofibromas.

              Background Effective medical therapies are lacking for the treatment of neurofibromatosis type 1-related plexiform neurofibromas, which are characterized by elevated RAS-mitogen-activated protein kinase (MAPK) signaling. Methods We conducted a phase 1 trial of selumetinib (AZD6244 or ARRY-142886), an oral selective inhibitor of MAPK kinase (MEK) 1 and 2, in children who had neurofibromatosis type 1 and inoperable plexiform neurofibromas to determine the maximum tolerated dose and to evaluate plasma pharmacokinetics. Selumetinib was administered twice daily at a dose of 20 to 30 mg per square meter of body-surface area on a continuous dosing schedule (in 28-day cycles). We also tested selumetinib using a mouse model of neurofibromatosis type 1-related neurofibroma. Response to treatment (i.e., an increase or decrease from baseline in the volume of plexiform neurofibromas) was monitored by using volumetric magnetic resonance imaging analysis to measure the change in size of the plexiform neurofibroma. Results A total of 24 children (median age, 10.9 years; range, 3.0 to 18.5) with a median tumor volume of 1205 ml (range, 29 to 8744) received selumetinib. Patients were able to receive selumetinib on a long-term basis; the median number of cycles was 30 (range, 6 to 56). The maximum tolerated dose was 25 mg per square meter (approximately 60% of the recommended adult dose). The most common toxic effects associated with selumetinib included acneiform rash, gastrointestinal effects, and asymptomatic creatine kinase elevation. The results of pharmacokinetic evaluations of selumetinib among the children in this trial were similar to those published for adults. Treatment with selumetinib resulted in confirmed partial responses (tumor volume decreases from baseline of ≥20%) in 17 of the 24 children (71%) and decreases from baseline in neurofibroma volume in 12 of 18 mice (67%). Disease progression (tumor volume increase from baseline of ≥20%) has not been observed to date. Anecdotal evidence of decreases in tumor-related pain, disfigurement, and functional impairment was observed. Conclusions Our early-phase data suggested that children with neurofibromatosis type 1 and inoperable plexiform neurofibromas benefited from long-term dose-adjusted treatment with selumetinib without having excess toxic effects. (Funded by the National Institutes of Health and others; ClinicalTrials.gov number, NCT01362803 .).
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                Author and article information

                Journal
                Dis Model Mech
                Dis Model Mech
                DMM
                dmm
                Disease Models & Mechanisms
                The Company of Biologists Ltd
                1754-8403
                1754-8411
                1 February 2022
                1 February 2022
                1 February 2022
                : 15
                : 2 , Special Issue: The RAS Pathway
                : dmm049344
                Affiliations
                [1 ]Department of Pediatrics, Division of Genomic Medicine, University of California Davis , Sacramento, CA 95817, USA
                [2 ]Department of Pediatrics, UC Davis MIND Institute , Sacramento, CA 95817, USA
                Author notes
                [* ]Author for correspondence ( rauen@ 123456ucdavis.edu )
                Author information
                http://orcid.org/0000-0003-1719-7228
                Article
                DMM049344
                10.1242/dmm.049344
                8821523
                35103797
                268525cc-cf93-4f39-9463-e6d5048ed776
                © 2022. Published by The Company of Biologists Ltd

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.

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                Molecular medicine
                Molecular medicine

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