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SMAD4
SMAD family member 4
The SMAD4 gene provides instructions for a protein crucial in cellular signalling, regulating cell growth and division, and acting as a tumour suppressor. The SMAD4 gene encodes a protein that plays a central role in the transforming growth factor beta (TGF-β) signalling pathway, mediating signals from the cell surface to the nucleus.
SMAD4 is located on the long (q) arm of chromosome 18, at band 18q21.2. Arm ratio per GRCh38 - banding schematic.
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Overview
The SMAD4 gene is an important component of the cellular machinery responsible for transmitting signals that regulate cell growth, division, and differentiation. It encodes a protein known as Mothers Against Decapentaplegic Homolog 4, which is a key mediator within the TGF-β signalling pathway. This pathway is fundamental to many biological processes, including embryonic development, tissue repair, and immune regulation.
Dysfunction of the SMAD4 protein, often due to pathogenic variants in the SMAD4 gene, can lead to various health conditions. These include certain inherited cancer predisposition syndromes and vascular disorders. Understanding the role of SMAD4 is therefore critical for comprehending the genetic basis of these conditions and for developing potential therapeutic strategies.
What the gene does
The SMAD4 gene produces a protein that acts as a central mediator in the transforming growth factor beta (TGF-β) signalling pathway. This pathway initiates when a TGF-β protein binds to its receptor on the cell surface, activating a group of related SMAD proteins. These activated SMAD proteins then associate with the SMAD4 protein to form a complex, which subsequently translocates into the cell nucleus.
Within the nucleus, this SMAD protein complex binds to specific DNA regions, thereby influencing the activity of particular genes. This regulation of gene activity is crucial for controlling processes such as cell growth and division (proliferation). Consequently, the SMAD4 protein contributes significantly to the development of numerous bodily systems.
Beyond its role in signal transduction, the SMAD4 protein functions as both a transcription factor and a tumour suppressor. As a transcription factor, it helps to modulate the expression of specific genes. As a tumour suppressor, it plays a vital role in preventing cells from growing and dividing excessively or in an uncontrolled manner, thereby safeguarding against tumour formation.
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Chromosome location
The SMAD4 gene is situated on chromosome 18, specifically at band 18q21.2. This location refers to the long (q) arm of chromosome 18, within region 2, band 1, and sub-band 2. Chromosomes are highly organised structures found within the nucleus of eukaryotic cells, carrying genetic information in the form of DNA. The precise genomic coordinates help researchers locate the gene and understand its genetic neighbourhood, which can be relevant for inherited conditions like Edwards syndrome, a chromosomal disorder.
Protein structure
The SMAD4 protein consists of 552 amino acids and features several distinct regions and domains crucial for its function. The N-terminal region of the protein, spanning amino acids 1-322, mediates interactions with the ZBTB7A protein. Within this N-terminal part, the MH1 domain (amino acids 18-142) is present, which is essential for DNA binding and nuclear localisation. A specific segment from amino acids 44-69 is required for interaction with the TSC22D1 protein.
The protein also contains two distinct disordered regions, located at amino acids 168-194 and 236-256, respectively. These regions often contribute to protein flexibility and interactions. The SAD region, encompassing amino acids 275-320, is involved in SMAD activation and nuclear translocation. Finally, the C-terminal portion of the protein is characterised by the MH2 domain, spanning amino acids 323-552. This domain is critical for protein-protein interactions and signal transduction within the TGF-β pathway.
Key variants
Variants within the SMAD4 gene can alter the protein's structure or function, impacting its role in cellular signalling and tumour suppression. These changes can range from single nucleotide substitutions to larger deletions or insertions within the gene sequence. Depending on their nature and location, such variants may lead to a non-functional or abnormally short SMAD4 protein, disrupting the TGF-β signalling pathway. The clinical consequences of SMAD4 variants are diverse, contributing to a spectrum of inherited disorders with varying severities and implications for health. Individuals carrying certain SMAD4 variants may have an increased predisposition to specific conditions.
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.731_732insGCCC(p.Gln245Profs) | p.Gln245Profs | Pathogenic | ★★☆☆ | Familial thoracic aortic aneurysm and aortic dissection |
c.1023del | p.Pro342fs | Pathogenic | ★★☆☆ | Juvenile polyposis syndrome |
c.1028C>G | p.Ser343Ter | Pathogenic | ★★☆☆ | Familial thoracic aortic aneurysm and aortic dissection |
c.1045dup | p.Thr349fs | Pathogenic | ★★☆☆ | not provided |
c.1052A>T | p.Asp351Val | Pathogenic/Likely pathogenic | ★★☆☆ | Juvenile polyposis syndrome |
c.1054G>A | p.Gly352Arg | Pathogenic/Likely pathogenic | ★★☆☆ | Juvenile polyposis/hereditary hemorrhagic telangiectasia syndrome |
c.1059C>A | p.Tyr353Ter | Pathogenic | ★★☆☆ | Familial thoracic aortic aneurysm and aortic dissection |
c.1059C>G | p.Tyr353Ter | Pathogenic/Likely pathogenic | ★★☆☆ | not provided |
c.1067del | p.Pro356fs | Pathogenic | ★★☆☆ | Juvenile polyposis syndrome |
c.1081C>G | p.Arg361Gly | Pathogenic | ★★☆☆ | Juvenile polyposis 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
Pathogenic variants in the SMAD4 gene are associated with several inherited conditions, primarily affecting cell growth regulation and vascular development. These include Juvenile polyposis syndrome, characterised by the development of multiple non-cancerous growths called juvenile polyps in the gastrointestinal tract. Another associated condition is Hereditary haemorrhagic telangiectasia type 1, which involves abnormal blood vessel formation, leading to characteristic arteriovenous malformations. Additionally, SMAD4 variants have been implicated in an increased risk of developing various cancers due to its role as a tumour suppressor.
Inheritance pattern
Conditions caused by pathogenic SMAD4 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 SMAD4 gene is recognised on several NHS Genomic Medicine Service (GMS) pathways, reflecting its significance in clinical genomics. It is listed as 'green' on numerous PanelApp panels, indicating strong evidence for its association with specific conditions and its relevance for diagnostic testing. These panels include 'Adult solid tumours cancer susceptibility' and 'Childhood solid tumours cancer susceptibility', highlighting its role in cancer predisposition. Furthermore, SMAD4 is featured on panels for 'Hereditary haemorrhagic telangiectasia', 'Inherited polyposis and early onset colorectal cancer - germline testing', and 'Cerebral vascular malformations', underscoring its involvement in these distinct clinical presentations.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
Maintaining a healthy lifestyle, including a balanced diet and regular physical activity, is generally recommended for overall well-being. For individuals with conditions associated with SMAD4 variants, such as those that increase cancer risk, avoiding known carcinogens like tobacco and excessive alcohol consumption is prudent. Research suggests that a diet rich in fruits, vegetables, and whole grains may support cellular health and potentially reduce the risk of certain cancers in the general population, although specific dietary interventions for individuals with SMAD4 variants require further study and should be discussed with a healthcare professional.
Supplement considerations
There is no conclusive evidence to suggest that specific supplements can prevent or treat conditions associated with SMAD4 gene variants. While some nutrients and compounds are recognised for their general health benefits, their direct impact on the progression or manifestation of conditions linked to SMAD4 dysfunction has not been established. Individuals considering taking any supplements should consult with a healthcare provider to ensure their safety and appropriateness, particularly given potential interactions with medications or existing health conditions.
Frequently asked questions
What is the primary function of the SMAD4 gene?
The SMAD4 gene provides instructions for making a protein that is a central component of the TGF-β signalling pathway. This protein transmits signals from the cell surface to the nucleus, regulating gene activity, cell growth, and division, and also acts as a tumour suppressor.
What health conditions are associated with variants in the SMAD4 gene?
Pathogenic variants in the SMAD4 gene are associated with conditions such as Juvenile polyposis syndrome and Hereditary haemorrhagic telangiectasia type 1. They are also linked to an increased risk of developing various cancers due to the gene's role as a tumour suppressor.
Is SMAD4 involved in cancer?
Yes, the SMAD4 protein functions as a tumour suppressor. Variants in the SMAD4 gene can lead to uncontrolled cell growth, increasing the risk of various cancers. Some mutations are inherited, while others are acquired during a person's lifetime.
Where is the SMAD4 gene located?
The SMAD4 gene is located on chromosome 18, specifically at band 18q21.2. This indicates its position on the long arm of chromosome 18.
How does the SMAD4 gene relate to cell signalling?
The SMAD4 gene encodes a protein that forms a complex with other SMAD proteins after activation by TGF-β signals. This complex then moves to the cell nucleus to bind DNA and regulate gene activity, thereby mediating external cellular signals.
References
- Lin AE, Alali A, Starr LJ. Gain-of-function pathogenic variants in SMAD4 are associated with neoplasia in Myhre syndrome. American journal of medical genetics. Part A. 2020. PMID: 31837202
- Meerschaut I, Beyens A, Steyaert W. Myhre syndrome: A first familial recurrence and broadening of the phenotypic spectrum. American journal of medical genetics. Part A. 2019. PMID: 31595668
- Lin AE, Michot C, Cormier-Daire V. Gain-of-function mutations in SMAD4 cause a distinctive repertoire of cardiovascular phenotypes in patients with Myhre syndrome. American journal of medical genetics. Part A. 2016. PMID: 27302097
- Caputo V, Bocchinfuso G, Castori M. Novel SMAD4 mutation causing Myhre syndrome. American journal of medical genetics. Part A. 2014. PMID: 24715504
- Teekakirikul P, Milewicz DM, Miller DT. Thoracic aortic disease in two patients with juvenile polyposis syndrome and SMAD4 mutations. American journal of medical genetics. Part A. 2013. PMID: 23239472
- Caputo V, Cianetti L, Niceta M. A restricted spectrum of mutations in the SMAD4 tumor-suppressor gene underlies Myhre syndrome. American journal of human genetics. 2012. PMID: 22243968
- Lindor NM, Gunawardena SR, Thibodeau SN. Mutations of SMAD4 account for both LAPS and Myhre syndromes. American journal of medical genetics. Part A. 2012. PMID: 22585601
- Andrabi S, Bekheirnia MR, Robbins-Furman P. SMAD4 mutation segregating in a family with juvenile polyposis, aortopathy, and mitral valve dysfunction. American journal of medical genetics. Part A. 2011. PMID: 21465659
- Le Goff C, Mahaut C, Abhyankar A. Mutations at a single codon in Mad homology 2 domain of SMAD4 cause Myhre syndrome. Nature genetics. 2011. PMID: 22158539
- Calva-Cerqueira D, Chinnathambi S, Pechman B. The rate of germline mutations and large deletions of SMAD4 and BMPR1A in juvenile polyposis. Clinical genetics. 2009. PMID: 18823382
- Aretz S, Stienen D, Uhlhaas S. High proportion of large genomic deletions and a genotype phenotype update in 80 unrelated families with juvenile polyposis syndrome. Journal of medical genetics. 2007. PMID: 17873119
- Pyatt RE, Pilarski R, Prior TW. Mutation screening in juvenile polyposis syndrome. The Journal of molecular diagnostics : JMD. 2006. PMID: 16436638
- Chow E, Macrae F. A review of juvenile polyposis syndrome. Journal of gastroenterology and hepatology. 2005. PMID: 16246179
- Gallione CJ, Repetto GM, Legius E. A combined syndrome of juvenile polyposis and hereditary haemorrhagic telangiectasia associated with mutations in MADH4 (SMAD4). Lancet (London, England). 2004. PMID: 15031030
- Howe JR, Sayed MG, Ahmed AF. The prevalence of MADH4 and BMPR1A mutations in juvenile polyposis and absence of BMPR2, BMPR1B, and ACVR1 mutations. Journal of medical genetics. 2004. PMID: 15235019
- Merg A, Howe JR. Genetic conditions associated with intestinal juvenile polyps. American journal of medical genetics. Part C, Seminars in medical genetics. 2004. PMID: 15264272
- Howe JR, Shellnut J, Wagner B. Common deletion of SMAD4 in juvenile polyposis is a mutational hotspot. American journal of human genetics. 2002. PMID: 11920286
- Woodford-Richens KL, Rowan AJ, Poulsom R. Comprehensive analysis of SMAD4 mutations and protein expression in juvenile polyposis: evidence for a distinct genetic pathway and polyp morphology in SMAD4 mutation carriers. The American journal of pathology. 2001. PMID: 11583957
- Adam MP, Bick S, Mirzaa GM. Myhre Syndrome. 1993. PMID: 28406602