Germline gain-of-function mutations in SOS1 cause Noonan syndrome Amy E Roberts 1,2,5 , Toshiyuki Araki 3,5 , Kenneth D Swanson 3,5 , Kate T Montgomery 1 , Taryn A Schiripo 1 , Victoria A Joshi 1,4 , Li Li 1 , Yosuf Yassin 1 , Alex M Tamburino 1 , Benjamin G Neel 3 & Raju S Kucherlapati 1 Noonan syndrome, the most common single-gene cause of congenital heart disease, is characterized by short stature, characteristic facies, learning problems and leukemia predisposition 1 . Gain-of-function mutations in PTPN11, encoding the tyrosine phosphatase SHP2, cause B50% of Noonan syndrome cases. SHP2 is required for RAS-ERK MAP kinase (MAPK) cascade activation 2 , and Noonan syndrome mutants enhance ERK activation ex vivo 3,4 and in mice 5 . KRAS mutations account for o5% of cases of Noonan syndrome 6 , but the gene(s) responsible for the remainder are unknown. We identified missense mutations in SOS1, which encodes an essential RAS guanine nucleotide-exchange factor (RAS-GEF), in B20% of cases of Noonan syndrome without PTPN11 mutation. The prevalence of specific cardiac defects differs in SOS1 mutation–associated Noonan syndrome. Noonan syndrome–associated SOS1 mutations are hypermorphs encoding products that enhance RAS and ERK activation. Our results identify SOS1 mutants as a major cause of Noonan syndrome, representing the first example of activating GEF mutations associated with human disease and providing new insights into RAS-GEF regulation. The genes that cause Noonan syndrome (MIM 163950) and the related cardiofaciocutaneous syndrome (CFC) (MIM 115150) encode members of the RAS-ERK pathway 7 . RAS genes (KRAS, HRAS, NRAS) encode small GTP-binding proteins that act as molecular switches. In their GDP-bound state, RAS proteins are inactive. Cell stimulation promotes GDP-GTP exchange, a process catalyzed by RAS-GEFs. RAS-GTP binds and helps activate several downstream effectors, including RAF family kinases (cRAF, BRAF, A-RAF), phosphatidyl- inositol 3-kinase and RAL-guanine nucleotide dissociation stimulator (RAL-GDS). Activated RAF phosphorylates and activates MEK1 and MEK2, which phosphorylate and activate ERK1 and ERK2. RAS proteins also have an intrinsic GTPase activity, which, aided by RAS-GTPase-activating proteins (RAS-GAPs), inactivates RAS. Hypermorphic PTPN11 (ref. 1) or KRAS (ref. 6) mutations cause Noonan syndrome, whereas mutations in BRAF , MAP2K1 (also known as MEK1) or MAP2K2 (also known as MEK2) (refs. 8,9) cause CFC. The common features of these disorders probably result from increased ERK activation 7 . Because Noonan syndrome and CFC are distinguishable, and CFC is caused by mutations in genes acting downstream in the RAS-ERK pathway, we investigated upstream components as candidate Noonan syndrome genes in 91 probands with a confirmed diagnosis of Noonan syndrome, 34 of whom (37%) had a PTPN11 mutation. We did not find any mutations in KRAS, BRAF , CSK, PTPN6, PAG1 MRAS or SOS2 in the remaining 57 cases. However, we did find 14 probands with mutations in SOS1 (Fig. 1). SOS1, located on chromosome 2p22.1, has 23 coding exons (Fig. 1a) and encodes a major RAS-GEF. One proband and an unaffected parent had a previously reported, although not validated, SNP encoding N1011S in SOS1. The other 13 each had one of nine previously unreported missense changes, affecting six exons: T266K, D309Y, Y337C, G434R, S548R and P655L (each found in a single proband); M269R (two probands); R552G (two probands), and E846K (three probands) (Fig. 1a–d and Table 1). All but one of these mutations affected evolutionarily conserved residues. Although several residues occur at the position cognate to D309 in other species, none is a hydrophobic amino acid, as in the case of D309Y. We did not find these variants in 188 chromosomes from normal individuals or in the Ensembl SNP database. Four Noonan syndrome cases associated with SOS1 mutations were believed to be familial and nine sporadic. In three of the former, the affected parent, as expected, had the same mutation; the parents of the fourth were deceased. In five sporadic cases, analysis of the parents confirmed that the mutations occurred de novo; samples were unavail- able for three others. In the remaining sporadic case, an apparently unaffected mother had the same SOS1 allele (P655L) as her affected child. Because we cannot be sure if P655L or N1011S are the result of bona fide mutations or polymorphisms, we conservatively place the Received 15 August; accepted 23 October; published online 3 December 2006; doi:10.1038/ng1926 1 Harvard Partners Center for Genetics and Genomics and Harvard Medical School, Boston, Massachusetts 02115, USA. 2 Division of Genetics, Department of Medicine, Children’s Hospital Boston and Harvard Medical School, Boston, Massachusetts 02115, USA. 3 Cancer Biology Program, Division of Hematology/Oncology, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02115, USA. 4 Department of Pathology, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA. 5 These authors contributed equally to this work. Correspondence should be addressed to B.N. (bneel@bidmc.harvard.edu). 70 VOLUME 39 [ NUMBER 1 [ JANUARY 2007 NATURE GENETICS LETTERS © 2007 Nature Publishing Group http://www.nature.com/naturegenetics