Skip navigation

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

URL of this page:

SOS1 gene

SOS Ras/Rac guanine nucleotide exchange factor 1

Normal Function

The SOS1 gene provides instructions for making a protein that is involved in controlling (regulating) the activation of the RAS/MAPK signaling pathway, which helps control several important cell functions. Specifically, the pathway regulates the growth and division of cells (proliferation), the process by which cells mature to carry out specific functions (differentiation), cell movement (migration), and the self-destruction of cells (apoptosis). Within the RAS/MAPK signaling pathway, the SOS1 protein regulates a protein, called Ras, that stimulates cells to grow and divide. This regulation tightly controls the growth of cells and tissues, and is especially important for proper embryonic development.

Health Conditions Related to Genetic Changes

Noonan syndrome

More than 55 mutations causing Noonan syndrome have been identified in the SOS1 gene. Noonan syndrome is characterized by mildly unusual facial characteristics, short stature, heart defects, bleeding problems, skeletal malformations, and many other signs and symptoms. The SOS1 gene mutations change single protein building blocks (amino acids) in the SOS1 protein. The resulting protein is either continuously turned on (active) or has prolonged activation, rather than promptly switching on and off in response to other cellular proteins. This increase in protein activity disrupts the regulation of the RAS/MAPK signaling pathway that controls cell functions such as growth and division. This misregulation can result in the heart defects, growth problems, skeletal abnormalities, and other features of Noonan syndrome.

More About This Health Condition

Other disorders

Mutations in the SOS1 gene can also cause hereditary gingival fibromatosis type 1. This disorder is characterized by a slowly progressive overgrowth of the tissue of the gums (gingiva). Too much of this tissue can impair teeth from emerging through the gums, which can cause difficulties in speech and chewing food. At least one mutation in the SOS1 gene has been shown to cause hereditary gingival fibromatosis type 1. This mutation is an addition of a single building block of DNA (nucleotide). The mutation inserts the nucleotide cytosine into an area of the gene called exon 21 (written 3248_3249insC) and disrupts the gene's instructions, resulting in a shortened protein. Unlike the normal SOS1 protein, the shortened protein is permanently active because it is missing areas that regulate its activity. Instead of triggering cell growth in response to particular signals from outside the cell, the overactive protein directs cells to grow and divide constantly. It is unclear why the overgrowth of tissue is seen only in the gums.

Other Names for This Gene

  • alternate SOS1
  • GF1
  • GGF1
  • gingival fibromatosis
  • gingival fibromatosis, hereditary, 1
  • HGF
  • son of sevenless homolog 1
  • son of sevenless homolog 1 (Drosophila)

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Gene and Variant Databases


  • Calcagni G, Baban A, De Luca E, Leonardi B, Pongiglione G, Digilio MC. Coronary artery ectasia in Noonan syndrome: Report of an individual with SOS1 mutation and literature review. Am J Med Genet A. 2016 Mar;170(3):665-9. doi: 10.1002/ajmg.a.37505. Epub 2015 Dec 21. Citation on PubMed
  • Hart TC, Zhang Y, Gorry MC, Hart PS, Cooper M, Marazita ML, Marks JM, Cortelli JR, Pallos D. A mutation in the SOS1 gene causes hereditary gingival fibromatosis type 1. Am J Hum Genet. 2002 Apr;70(4):943-54. doi: 10.1086/339689. Epub 2002 Feb 26. Citation on PubMed or Free article on PubMed Central
  • Jang SI, Lee EJ, Hart PS, Ramaswami M, Pallos D, Hart TC. Germ line gain of function with SOS1 mutation in hereditary gingival fibromatosis. J Biol Chem. 2007 Jul 13;282(28):20245-55. doi: 10.1074/jbc.M701609200. Epub 2007 May 17. Citation on PubMed
  • Martinez Planello A, Sotillo M, Rodriguez-Santos F. Cognitive profile of a child with SOS1 mutation in Noonan syndrome. Neurologia (Engl Ed). 2018 Mar;33(2):137-138. doi: 10.1016/j.nrl.2016.01.002. Epub 2016 Mar 8. No abstract available. English, Spanish. Citation on PubMed
  • Roberts AE, Araki T, Swanson KD, Montgomery KT, Schiripo TA, Joshi VA, Li L, Yassin Y, Tamburino AM, Neel BG, Kucherlapati RS. Germline gain-of-function mutations in SOS1 cause Noonan syndrome. Nat Genet. 2007 Jan;39(1):70-4. doi: 10.1038/ng1926. Epub 2006 Dec 3. Citation on PubMed
  • Romano AA, Allanson JE, Dahlgren J, Gelb BD, Hall B, Pierpont ME, Roberts AE, Robinson W, Takemoto CM, Noonan JA. Noonan syndrome: clinical features, diagnosis, and management guidelines. Pediatrics. 2010 Oct;126(4):746-59. doi: 10.1542/peds.2009-3207. Epub 2010 Sep 27. Citation on PubMed
  • Shannon K, Bollag G. Sending out an SOS. Nat Genet. 2007 Jan;39(1):8-9. doi: 10.1038/ng0107-8. No abstract available. Citation on PubMed
  • Tartaglia M, Pennacchio LA, Zhao C, Yadav KK, Fodale V, Sarkozy A, Pandit B, Oishi K, Martinelli S, Schackwitz W, Ustaszewska A, Martin J, Bristow J, Carta C, Lepri F, Neri C, Vasta I, Gibson K, Curry CJ, Siguero JP, Digilio MC, Zampino G, Dallapiccola B, Bar-Sagi D, Gelb BD. Gain-of-function SOS1 mutations cause a distinctive form of Noonan syndrome. Nat Genet. 2007 Jan;39(1):75-9. doi: 10.1038/ng1939. Epub 2006 Dec 13. Erratum In: Nat Genet. 2007 Feb;39(2):276. Citation on PubMed
  • Zenker M, Horn D, Wieczorek D, Allanson J, Pauli S, van der Burgt I, Doerr HG, Gaspar H, Hofbeck M, Gillessen-Kaesbach G, Koch A, Meinecke P, Mundlos S, Nowka A, Rauch A, Reif S, von Schnakenburg C, Seidel H, Wehner LE, Zweier C, Bauhuber S, Matejas V, Kratz CP, Thomas C, Kutsche K. SOS1 is the second most common Noonan gene but plays no major role in cardio-facio-cutaneous syndrome. J Med Genet. 2007 Oct;44(10):651-6. doi: 10.1136/jmg.2007.051276. Epub 2007 Jun 23. Citation on PubMed or Free article on PubMed Central

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.