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FBN1
fibrillin 1
The FBN1 gene provides instructions for producing fibrillin-1, a crucial protein that forms microfibrils, essential components of the extracellular matrix and connective tissues throughout the body. FBN1 encodes fibrillin-1, a large protein integral to the structural integrity and elasticity of various tissues.
FBN1 is located on the long (q) arm of chromosome 15, at band 15q21.1. Arm ratio per GRCh38 - banding schematic.
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Overview
The FBN1 gene is responsible for synthesising fibrillin-1, a key structural protein in the human body. Fibrillin-1 is a major component of microfibrils, which are thread-like filaments found within the extracellular matrix-the intricate network of proteins and molecules surrounding cells [PMID:18420993]. These microfibrils are crucial for the assembly of elastic fibres, providing tissues like skin, ligaments, and blood vessels with their characteristic stretch and recoil properties. Beyond its structural role, fibrillin-1 also plays a regulatory function by controlling the activity of certain growth factors, particularly transforming growth factor beta (TGF-β).
Dysfunction of the FBN1 gene can lead to a range of connective tissue disorders, collectively known as fibrillinopathies. The most well-known condition associated with FBN1 variants is Marfan syndrome, which affects the skeletal, ocular, and cardiovascular systems. Understanding the FBN1 gene and its protein product is therefore vital for comprehending the pathology of these complex conditions and developing targeted management strategies [PMID:24075133].
What the gene does
The FBN1 gene encodes fibrillin-1, a large glycoprotein that is fundamental to the architecture and function of the extracellular matrix. Once synthesised, fibrillin-1 is secreted from cells and integrates into the extracellular matrix, where it polymerises to form microfibrils [PMID:18420993]. These microfibrils act as a scaffold, facilitating the organisation of elastic fibres, which are crucial for the resilience and elasticity of connective tissues in organs such as the aorta, skin, lungs, and ligaments.
In addition to its structural role, fibrillin-1 is involved in regulating the bioavailability and activity of growth factors, notably members of the transforming growth factor beta (TGF-β) superfamily. Fibrillin-1 microfibrils serve as a reservoir for latent TGF-β complexes, sequestering them and preventing their premature activation. When released from the microfibrillar network, active TGF-β can then signal through various pathways, influencing cell proliferation, differentiation, migration, and apoptosis [PMID:18420993]. This regulatory capacity highlights fibrillin-1's role in tissue homeostasis and repair, as aberrant TGF-β signalling is implicated in the pathogenesis of several connective tissue disorders. For instance, dysregulation of TGF-β activity due to FBN1 variants can contribute to the skeletal, ocular, and cardiovascular manifestations observed in conditions like Marfan syndrome [PMID:24075133]. The precise balance of TGF-β storage and release mediated by fibrillin-1 is therefore critical for maintaining healthy tissue structure and function.
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Chromosome location
The FBN1 gene is located on the long arm of chromosome 15 at position 21.1, which is denoted as 15q21.1. This specific genomic address places FBN1 within a region of chromosome 15 that is frequently studied in the context of connective tissue disorders. The gene spans a significant length of DNA, encoding a protein comprising 2871 amino acids.
Protein structure
The fibrillin-1 protein, encoded by the FBN1 gene, is a large glycoprotein with a complex domain organisation. It comprises several distinct regions and domains crucial for its structural and regulatory functions. The N-terminal domain spans amino acids 45-450, within which lies the Fibrillin unique N-terminal (FUN) domain from amino acids 45-81. The protein features numerous Epidermal Growth Factor (EGF)-like domains, including EGF-like 1 (amino acids 81-112), EGF-like 2 (amino acids 115-146), EGF-like 3 (amino acids 147-178), EGF-like 4; calcium-binding (amino acids 246-287), EGF-like 5; calcium-binding (amino acids 288-329), EGF-like 6 (amino acids 449-489), EGF-like 7; calcium-binding (amino acids 490-529), EGF-like 8; calcium-binding (amino acids 530-571), and EGF-like 9; calcium-binding (amino acids 572-612).
Additionally, fibrillin-1 contains multiple Transforming Growth Factor beta binding protein (TB) domains, such as TB 1 (amino acids 184-236) and TB 2 (amino acids 334-389). A Hybrid domain 1 is also noted from amino acids 195-221. An important functional region for protein-protein interaction, specifically with MFAP4, is located between amino acids 119-329. The presence of calcium-binding EGF-like domains highlights the protein's reliance on calcium for proper folding and function, which is critical for its role in microfibril assembly and extracellular matrix integrity.
Key variants
Variants in the FBN1 gene encompass a wide spectrum of genetic changes, including missense, nonsense, frameshift, and splicing alterations. These variants can lead to a deficiency of functional fibrillin-1 protein or result in the production of a malformed protein that interferes with normal microfibril assembly and function. The location and type of variant often correlate with the specific clinical presentation, influencing the severity and manifestations of associated conditions. Pathogenic variants can affect various domains of the fibrillin-1 protein, impacting its ability to polymerise into microfibrils or regulate growth factors like TGF-β.
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 |
|---|---|---|---|---|
g.48415536delinsAA | - | Pathogenic | ★★★☆ | Marfan syndrome |
c.1453C>T | p.Arg485Cys | Pathogenic | ★★★☆ | MARFAN SYNDROME, AUTOSOMAL RECESSIVE |
c.1556A>G | p.Tyr519Cys | Pathogenic | ★★★☆ | Marfan syndrome |
c.1630G>A | p.Gly544Arg | Pathogenic | ★★★☆ | Familial thoracic aortic aneurysm and aortic dissection |
c.1708T>C | p.Cys570Arg | Pathogenic | ★★★☆ | Familial thoracic aortic aneurysm and aortic dissection |
c.1850G>A | p.Cys617Tyr | Pathogenic | ★★★☆ | not provided |
c.1A>C | p.Met1Leu | Pathogenic | ★★★☆ | Marfan Syndrome/Loeys-Dietz Syndrome/Familial Thoracic Aortic Aneurysms and Dissections |
c.2287T>G | p.Cys763Gly | Pathogenic | ★★★☆ | Marfan syndrome |
c.3290G>A | p.Cys1097Tyr | Pathogenic | ★★★☆ | Marfan syndrome |
c.3476G>A | p.Cys1159Tyr | Pathogenic | ★★★☆ | Marfan 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 FBN1 gene are primarily associated with Marfan syndrome, an autosomal dominant connective tissue disorder. Beyond Marfan syndrome, FBN1 variants have also been linked to a phenotypic spectrum that includes other conditions such as isolated ectopia lentis, acromicric dysplasia, geleophysic dysplasia, and Weill-Marchesani syndrome. These conditions, while distinct, share underlying defects in connective tissue integrity due to fibrillin-1 dysfunction, affecting various organ systems, including the skeletal, ocular, and cardiovascular systems.
Inheritance pattern
Conditions caused by pathogenic FBN1 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 FBN1 gene is recognised within the NHS Genomic Medicine Service (GMS) pathways, indicating its clinical significance for diagnostic testing and patient management. It is included on several green-rated panels in PanelApp, signifying strong evidence for its association with specific conditions. These panels include 'DDG2P', 'Ehlers Danlos syndrome with a likely monogenic cause (R101)', 'Foetal anomalies (R21)', 'Pneumothorax - familial (R190)', 'Rare syndromic craniosynostosis or isolated multisuture synostosis (R100)', 'Severe insulin resistance and lipodystrophy syndromes (R158)', 'Skeletal dysplasia (R104)', 'Structural eye disease (R36)', 'Thoracic aortic aneurysm or dissection', and 'Thoracic aortic aneurysm or dissection (GMS) (R125)'. The gene is also classified under the ACMG SF v3.2 - Secondary Findings category as a Tier 1 actionable gene, highlighting its importance for incidental findings in genomic sequencing.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
For individuals with FBN1-related conditions, lifestyle modifications are often recommended to manage symptoms and reduce the risk of complications. Generally, avoiding activities that place excessive strain on connective tissues is advised. For example, individuals with Marfan syndrome are typically counselled to avoid contact sports, heavy lifting, and sudden strenuous physical activity due to the increased risk of aortic dissection or rupture [PMID:24075133]. Regular, low-impact exercise, such as walking or swimming, may be beneficial for maintaining cardiovascular health and muscle tone without overstressing vulnerable tissues. Maintaining a healthy weight through a balanced diet can also help reduce the burden on the cardiovascular system and joints. Furthermore, avoiding smoking is crucial, as it can negatively impact connective tissue health and accelerate vascular degeneration. Research suggests that a heart-healthy diet, rich in fruits, vegetables, and whole grains, may support overall well-being, though no specific diet can prevent the progression of FBN1-related conditions. Individualised advice from healthcare professionals, including cardiologists and geneticists, is essential for tailoring lifestyle recommendations.
Supplement considerations
Currently, there is no conclusive scientific evidence to suggest that specific dietary supplements can prevent or treat conditions associated with pathogenic FBN1 variants. While some research explores the potential roles of various nutrients in connective tissue health, these findings are not specific to FBN1-related disorders. For instance, some studies have investigated compounds that might modulate TGF-β signalling, which is often dysregulated in FBN1 conditions, but these are generally in experimental stages and not recommended as clinical interventions [PMID:24075133]. Individuals considering any supplements should consult with a healthcare professional, such as their GP or a registered dietitian, to discuss potential benefits, risks, and interactions with any existing medications or health conditions. It is important to prioritise conventional medical management and adhere to prescribed treatments for FBN1-related disorders.
Frequently asked questions
What is the FBN1 gene?
The FBN1 gene provides genetic instructions for making fibrillin-1, a protein vital for forming microfibrils, which are key components of the extracellular matrix and essential for the structure and elasticity of connective tissues.
What does fibrillin-1 do in the body?
Fibrillin-1 helps build elastic fibres, providing stretch and support to tissues like skin, blood vessels, and ligaments. It also regulates growth factors, particularly TGF-β, which influences cell growth and development.
Which conditions are associated with FBN1 variants?
Pathogenic variants in FBN1 are primarily associated with Marfan syndrome, but also with isolated ectopia lentis, acromicric dysplasia, geleophysic dysplasia, and Weill-Marchesani syndrome.
How are FBN1-related conditions inherited?
FBN1-related conditions, such as Marfan syndrome, generally follow an autosomal dominant inheritance pattern, meaning only one copy of a pathogenic FBN1 variant is sufficient to cause the condition.
Can lifestyle changes help manage FBN1-related conditions?
Yes, certain lifestyle adjustments, such as avoiding strenuous activities and maintaining a healthy diet, can help manage symptoms and reduce the risk of complications in individuals with FBN1-related conditions, especially Marfan syndrome.
Are there specific supplements for FBN1-related conditions?
Currently, there is no conclusive evidence that specific dietary supplements can prevent or treat FBN1-related conditions. Any supplement use should be discussed with a healthcare professional.
References
- Chandra A, Patel D, Aragon-Martin JA. The revised ghent nosology; reclassifying isolated ectopia lentis. Clinical genetics. 2015. PMID: 24635535
- Le Goff C, Mahaut C, Wang LW. Mutations in the TGFβ binding-protein-like domain 5 of FBN1 are responsible for acromicric and geleophysic dysplasias. American journal of human genetics. 2011. PMID: 21683322
- Loeys BL, Gerber EE, Riegert-Johnson D. Mutations in fibrillin-1 cause congenital scleroderma: stiff skin syndrome. Science translational medicine. 2010. PMID: 20375004
- Faivre L, Collod-Beroud G, Callewaert B. Pathogenic FBN1 mutations in 146 adults not meeting clinical diagnostic criteria for Marfan syndrome: further delineation of type 1 fibrillinopathies and focus on patients with an isolated major criterion. American journal of medical genetics. Part A. 2009. PMID: 19353630
- Mizuguchi T, Matsumoto N. Recent progress in genetics of Marfan syndrome and Marfan-associated disorders. Journal of human genetics. 2007. PMID: 17061023
- Faivre L, Collod-Beroud G, Loeys BL. Effect of mutation type and location on clinical outcome in 1,013 probands with Marfan syndrome or related phenotypes and FBN1 mutations: an international study. American journal of human genetics. 2007. PMID: 17701892
- Robinson PN, Arteaga-Solis E, Baldock C. The molecular genetics of Marfan syndrome and related disorders. Journal of medical genetics. 2006. PMID: 16571647
- Arbustini E, Grasso M, Ansaldi S. Identification of sixty-two novel and twelve known FBN1 mutations in eighty-one unrelated probands with Marfan syndrome and other fibrillinopathies. Human mutation. 2005. PMID: 16222657
- Faivre L, Gorlin RJ, Wirtz MK. In frame fibrillin-1 gene deletion in autosomal dominant Weill-Marchesani syndrome. Journal of medical genetics. 2003. PMID: 12525539
- Dietz HC, McIntosh I, Sakai LY. Four novel FBN1 mutations: significance for mutant transcript level and EGF-like domain calcium binding in the pathogenesis of Marfan syndrome. Genomics. 1993. PMID: 8406497
- Glesby MJ, Pyeritz RE. Association of mitral valve prolapse and systemic abnormalities of connective tissue. A phenotypic continuum. JAMA. 1989. PMID: 2739055