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SOS1
SOS Ras/Rac guanine nucleotide exchange factor 1
The SOS1 gene provides instructions for a protein that plays a key role in regulating cell growth, division, and differentiation by controlling the RAS/MAPK signalling pathway. The SOS1 gene encodes a protein that acts as a guanine nucleotide exchange factor (GEF), primarily regulating the activation of Ras proteins within the RAS/MAPK pathway.
SOS1 is located on the short (p) arm of chromosome 2, at band 2p22.1. Arm ratio per GRCh38 - banding schematic.
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Overview
The SOS1 gene, or SOS Ras/Rac guanine nucleotide exchange factor 1, is essential for orchestrating cellular responses to external cues. It produces a protein that is a critical component of the conserved RAS/MAPK signalling pathway, which governs fundamental biological processes. These processes include cellular growth, division, specialisation, and movement, making SOS1 vital for normal embryonic development and overall physiological function. [PMID:18492981]
Pathogenic variants within the SOS1 gene are associated with certain inherited conditions, notably Noonan syndrome, which affects multiple bodily systems. Understanding the role of SOS1 helps clarify the molecular basis of these conditions and their diverse clinical presentations.
What the gene does
The SOS1 protein functions as a guanine nucleotide exchange factor (GEF), specifically activating Ras and Rac proteins. Within the cell, Ras proteins act as molecular switches, cycling between an inactive, GDP-bound state and an active, GTP-bound state. The SOS1 protein facilitates this activation by promoting the release of GDP, allowing GTP to bind, thereby turning the Ras protein 'on'. This activation is a crucial step in initiating the RAS/MAPK signalling cascade.
The RAS/MAPK pathway is fundamental for numerous cellular activities, including regulating cell growth and proliferation, guiding cellular differentiation into specialised cell types, facilitating cell migration, and mediating programmed cell death (apoptosis). The precise control exerted by SOS1 over Ras activation is paramount for maintaining normal cellular homeostasis and development. Dysregulation, such as through activating variants, can lead to uncontrolled signalling, which has implications for various developmental disorders.
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Chromosome location
The SOS1 gene is located on the short arm of chromosome 2, specifically at position 2p22.1. This genomic address specifies the precise band on the chromosome where the gene resides. The human genome is organised into 23 pairs of chromosomes, and chromosome 2 is one of the larger ones, carrying a substantial number of genes. The SOS1 gene spans a significant region of this chromosomal segment, providing the genetic blueprint for its relatively large protein product.
Protein structure
The SOS1 protein is composed of 1333 amino acids and features several distinct functional domains. Towards the N-terminus, it contains a DH (Dbl homology) domain, spanning amino acids 200-390, which is typically involved in Rho-family GTPase regulation. Following this is a PH (Pleckstrin homology) domain, located between amino acids 444-548, often implicated in membrane localisation and protein-lipid interactions. A pivotal N-terminal Ras-GEF domain exists from amino acids 597-741, preceding the main Ras-GEF domain found between amino acids 780-1019. These GEF domains are directly responsible for the protein's guanine nucleotide exchange activity on Ras proteins. The C-terminal region of the protein includes two disordered regions, one from amino acids 1019-1103 and another from 1129-1333, which may contribute to flexible protein-protein interactions or regulatory mechanisms.
Key variants
Variants within the SOS1 gene can alter the protein's normal function, leading to various clinical manifestations. These genetic changes often involve single nucleotide substitutions affecting individual protein building blocks (amino acids). Pathogenic variants can result in altered protein function, often increasing its activity. This gain-of-function effect can lead to persistent activation of the downstream RAS/MAPK signalling pathway, disrupting the intricate balance required for normal cellular processes and development.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1642A>C | p.Ser548Arg | Pathogenic | ★★★☆ | Noonan syndrome |
c.1654A>G | p.Arg552Gly | Pathogenic | ★★★☆ | Noonan syndrome |
c.1655G>A | p.Arg552Lys | Pathogenic | ★★★☆ | Noonan syndrome |
c.1655G>C | p.Arg552Thr | Pathogenic | ★★★☆ | Noonan syndrome |
c.1656G>C | p.Arg552Ser | Pathogenic | ★★★☆ | RASopathy |
c.1656G>T | p.Arg552Ser | Pathogenic | ★★★☆ | Noonan syndrome and Noonan-related syndrome |
c.2536G>A | p.Glu846Lys | Pathogenic | ★★★☆ | Noonan syndrome |
c.322G>A | p.Glu108Lys | Pathogenic | ★★★☆ | Noonan syndrome |
c.508A>G | p.Lys170Glu | Pathogenic | ★★★☆ | Noonan syndrome |
c.806T>C | p.Met269Thr | Pathogenic | ★★★☆ | Noonan syndrome |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Variants in the SOS1 gene are predominantly associated with Noonan syndrome, an autosomal dominant genetic condition [PMID:14634732]. Noonan syndrome is characterised by a diverse range of features, which can include distinctive facial characteristics, short stature, heart defects, bleeding tendencies, and bone abnormalities. Additionally, SOS1 gene variants can also be implicated in hereditary gingival fibromatosis type 1, a condition defined by progressive overgrowth of gum tissue, which can potentially impact tooth eruption, speech, and chewing.
Inheritance pattern
Conditions caused by pathogenic SOS1 variants typically follow autosomal dominant inheritance.
Each child has a 50% chance of inheriting the pathogenic variant, regardless of sex.
UK clinical status
In the UK, the SOS1 gene is routinely analysed within several NHS Genomic Medicine Service (GMS) panels, reflecting its established clinical significance. It is included in panels for Adult solid tumours cancer susceptibility, Childhood solid tumours, and Childhood solid tumours cancer susceptibility. Furthermore, SOS1 is covered by panels for conditions such as DDG2P (Developmental Disorders Genotyping Panel), Embryonal tumour of possible germline origin (R456), Foetal anomalies (R21), Foetal hydrops, Intellectual disability (R29), IUGR and IGF abnormalities, Monogenic short stature (R453), Paediatric or syndromic cardiomyopathy (R135), Pigmentary skin disorders (R236), and Primary lymphoedema (R136). It is also part of the broader RASopathies panel, indicating its role in this group of related conditions.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
Research into the impact of general lifestyle factors on conditions directly linked to SOS1 gene variants is ongoing. Maintaining a balanced diet, engaging in regular physical activity, and avoiding smoking and excessive alcohol consumption are generally recommended for overall health and well-being. These broad lifestyle choices support cardiovascular health and reduce general disease risk. However, there is no conclusive evidence to suggest that specific lifestyle interventions can prevent the onset or alter the progression of conditions caused by SOS1 variants. [PMID:33671427]
Supplement considerations
There is currently no definitive scientific evidence to support the use of specific dietary supplements for preventing or treating conditions associated with SOS1 gene variants. While some supplements may be advertised for general health benefits, their efficacy in the context of specific genetic conditions is not established. Individuals considering any supplements should consult with a healthcare professional to discuss potential benefits, risks, and interactions with other medications.
Frequently asked questions
What is the primary function of the SOS1 gene?
The SOS1 gene provides instructions for creating a protein that activates Ras proteins, which are key components of the RAS/MAPK signalling pathway. This pathway controls vital cell functions like growth, division, and differentiation.
What is Noonan syndrome, and how is it related to SOS1?
Noonan syndrome is an inherited condition characterised by various features including distinct facial traits, short stature, and heart defects. It is often caused by pathogenic variants in the SOS1 gene, which lead to hyperactivation of the RAS/MAPK pathway.
Are there other conditions associated with SOS1 gene variants?
Yes, beyond Noonan syndrome, variants in the SOS1 gene can also cause hereditary gingival fibromatosis type 1, a condition involving the overgrowth of gum tissue.
How common are SOS1 gene variants?
While specific prevalence figures are not provided, SOS1 gene variants are identified in a significant proportion of individuals diagnosed with Noonan syndrome, making it one of the common genetic causes for this condition.
Is the SOS1 gene considered clinically actionable in the UK?
Yes, the SOS1 gene is included in several NHS Genomic Medicine Service (GMS) panels in the UK, indicating its established clinical significance for diagnosing certain cancers and developmental disorders.
References
- Martínez Planelló A, Sotillo M, Rodríguez-Santos F. Cognitive profile of a child with SOS1 mutation in Noonan syndrome. Neurologia. 2018. PMID: 26968820
- Calcagni G, Baban A, De Luca E. Coronary artery ectasia in Noonan syndrome: Report of an individual with SOS1 mutation and literature review. American journal of medical genetics. Part A. 2016. PMID: 26686981
- Romano AA, Allanson JE, Dahlgren J. Noonan syndrome: clinical features, diagnosis, and management guidelines. Pediatrics. 2010. PMID: 20876176
- Tartaglia M, Pennacchio LA, Zhao C. Gain-of-function SOS1 mutations cause a distinctive form of Noonan syndrome. Nature genetics. 2007. PMID: 17143282
- Roberts AE, Araki T, Swanson KD. Germline gain-of-function mutations in SOS1 cause Noonan syndrome. Nature genetics. 2007. PMID: 17143285
- Shannon K, Bollag G. Sending out an SOS. Nature genetics. 2007. PMID: 17192780
- Jang SI, Lee EJ, Hart PS. Germ line gain of function with SOS1 mutation in hereditary gingival fibromatosis. The Journal of biological chemistry. 2007. PMID: 17510059
- Zenker M, Horn D, Wieczorek D. SOS1 is the second most common Noonan gene but plays no major role in cardio-facio-cutaneous syndrome. Journal of medical genetics. 2007. PMID: 17586837
- Hart TC, Zhang Y, Gorry MC. A mutation in the SOS1 gene causes hereditary gingival fibromatosis type 1. American journal of human genetics. 2002. PMID: 11868160