Contribution of RIT1 mutations to the pathogenesis of Noonan syndrome: Four new cases and further evidence of heterogeneity

Abstract

Noonan syndrome (NS) is a common developmental disorder presenting with dysmorphic craniofacial features, heart defects, and short stature. It belongs to the group of RASopathies caused by germline mutations in genes encoding proteins involved in the RAS/MAPK signaling pathway. Although mutations in nine genes are known to cause NS, approximately 30% of the cases still have unexplained etiology. To identify the new causative genes, 42 patients with a clinical diagnosis of NS, who had negative results on Sanger sequencing of PTPN11, SOS1, and RAF1 (the most common NS genes), were selected for whole exome sequencing. In two patients, mutations in recently described new NS gene—RIT1 were found (c.244T>G [p.Phe82Val] and c.270G>C [p.Met90Ile]). Further analysis of a larger cohort (n = 64) of NS patients with classic Sanger sequencing revealed the presence of RIT1 mutation c.284G>C (p.Gly95Ala) in two additional patients. All the detected mutations were localized in switch II domain responsible for GTPase activity. The modeling of RIT1 protein structure revealed that the mutated amino acids and their interacting residues are evolutionary conserved and any residue replacement might change the structural stability and/or protein internal dynamics influencing catalytic activity of the protein. It seems that the identified mutations might alter protein function and therefore, the activity of ERK and P38 MAPK pathways, thus underlying the specific phenotype observed in NS patients. Our study independently confirms the role of RIT1 in the pathogenesis of Noonan syndrome. © 2014 Wiley Periodicals, Inc.

A de novo 1q22q23.1 Interstitial Microdeletion in a Girl with Intellectual Disability and Multiple Congenital Anomalies Including Congenital Heart Defect

“…The encoded protein is involved in a wide variety of cellular processes, including cell proliferation, differen-tiation, and survival. It has been shown that different pathogenic variants in the RIT1 gene cause autosomal dominant Noonan syndrome through a gain-of-function mechanism resulting in increased RAS/MAPK signaling [Bertola et al, 2014;Gos et al, 2014;Milosavljević et al, 2016;Yaoita et al, 2016]. Recent reports have demonstrated that copy number variations containing disease-causing genes of RAS/MAPK pathway may be a pathogenetic mechanism for the etiology of RASopathies or related disorders [Graham et al, 2009;Luo et al, 2012;Chen et al, 2014].…”

Mutations in RIT1 cause Noonan syndrome with possible juvenile myelomonocytic leukemia but are not involved in acute lymphoblastic leukemia

“…Bertola et al 15 have described six Brazilian patients picked up by exome sequencing from a cohort of 70 NS patients who screened negative for PTPN11, SOS1, KRAS, RAF1, SHOC2, and CBL. Gos et al 16 have identified four RIT1-NS cases out G1 G2 G3…”

“…The second one has a more severe delay (DQ of 44 at 23 months) but a mild craniofacial phenotype (see Aoki's Figures 1a and d). Interestingly, the two causative mutations (p.Met90Ile and p.Phe82Leu) were subsequently found in patients clinically diagnosed as NS (by Gos et al 16 and by ourselves), illustrating the well-known challenge of intrinsic variability of most RASopathy mutations, and the limits of clinically based differential diagnosis of NS and CFC.…”

“…The involvement of RIT1 mutations in some cases of NS was subsequently confirmed in 14 other patients by others. 12,15,16 RIT1 is a widely expressed small GTPase belonging to a subfamily of the RAS family. It has 50% sequence homology with classic RAS GTPases (KRAS, HRAS, NRAS), and shows canonical GTPase activity but lacks the prenylation motif (CAAX, XXCC or CXC) required for its association with the plasma membrane.…”

Biochemical Classification of Disease-associated Mutants of RAS-like Protein Expressed in Many Tissues (RIT1)

“…Mutations-To deepen our understanding of the mechanistic rationale for the GTPase cycle defects of the RIT1 mutants, we modeled them using the structure of RIT1-GDP (PDB code 4KLZ) recently solved by Siegal and co-workers, 7 and gained insight into these mutations from the extensive literature available on characterization of RAS mutations.…”