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Clin Genet. 2016 Mar;89(3):359-66. doi: 10.1111/cge.12608. Epub 2015 Jun 4.

Mutations in RIT1 cause Noonan syndrome - additional functional evidence and expanding the clinical phenotype.

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Department of Otorhinolaryngology, Medical University of Vienna, Vienna, Austria.
Division of Genetics and Genomics, Boston Children's Hospital, Boston, MA, USA.
Dr. John T. Macdonald Foundation Department of Human Genetics, Miller School of Medicine, University of Miami, Miami, FL, USA.
Harvard Medical School, Boston, MA, USA.
John P. Hussman Institute for Human Genomics, Miller School of Medicine, University of Miami, Miami, FL, USA.
Department of Biology, University of Miami, Miami, FL, USA.
Bioinformatics Institute A*STAR Singapore, Singapore.
Division of Medical Genetics, Alfred I. duPont Hospital for Children, Wilmington, DE, USA.
Department of Pediatrics, Division of Pediatric Cardiology, Miller School of Medicine, University of Miami, Miami, FL, USA.
Department of Molecular and Cellular Biochemistry, College of Medicine, University of Kentucky, Lexington, KY, USA.


RASopathies are a clinically heterogeneous group of conditions caused by mutations in 1 of 16 proteins in the RAS-mitogen activated protein kinase (RAS-MAPK) pathway. Recently, mutations in RIT1 were identified as a novel cause for Noonan syndrome. Here we provide additional functional evidence for a causal role of RIT1 mutations and expand the associated phenotypic spectrum. We identified two de novo missense variants p.Met90Ile and p.Ala57Gly. Both variants resulted in increased MEK-ERK signaling compared to wild-type, underscoring gain-of-function as the primary functional mechanism. Introduction of p.Met90Ile and p.Ala57Gly into zebrafish embryos reproduced not only aspects of the human phenotype but also revealed abnormalities of eye development, emphasizing the importance of RIT1 for spatial and temporal organization of the growing organism. In addition, we observed severe lymphedema of the lower extremity and genitalia in one patient. We provide additional evidence for a causal relationship between pathogenic mutations in RIT1, increased RAS-MAPK/MEK-ERK signaling and the clinical phenotype. The mutant RIT1 protein may possess reduced GTPase activity or a diminished ability to interact with cellular GTPase activating proteins; however the precise mechanism remains unknown. The phenotypic spectrum is likely to expand and includes lymphedema of the lower extremities in addition to nuchal hygroma.


Costello syndrome; Noonan syndrome; RASopathy; RIT1

[Available on 2017-03-01]
[Indexed for MEDLINE]
Free PMC Article

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