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The Biology and Genetics of Marfan Syndrome

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Marfan syndrome is caused by mutations in the FBN1 gene, which alters the production of fibrillin-1 and weakens the body's connective tissue. While typically inherited from a parent with a 50% passing chance, up to 30% of cases result from new, spontaneous genetic mutations.

Key Takeaways

  • • Marfan syndrome is caused by mutations in the FBN1 gene, which weakens the connective tissue that acts as the body's scaffolding.
  • • Faulty fibrillin-1 protein leads to an overactivation of TGF-beta, causing the body to grow and change in ways it shouldn't.
  • • A parent with Marfan syndrome has a 50% chance of passing the genetic mutation to each child.
  • • About 25% to 30% of people with Marfan syndrome are the first in their family to have it due to a spontaneous de novo mutation.
  • • Different types of FBN1 mutations, such as haploinsufficiency or dominant-negative, can cause varying symptoms and specific health risks.

To understand Marfan syndrome, it helps to think of your body’s connective tissue as the scaffolding of a building or the rubber bands in a piece of fabric [1]. This tissue provides the strength and elasticity your body needs to hold everything in place—from your heart and lungs to your skin and joints. In Marfan syndrome, a genetic change causes this scaffolding to be weaker and less stable than it should be [2].

The FBN1 Gene and Fibrillin-1

The instructions for building this scaffolding are contained in a gene called FBN1 [1]. This gene tells your body how to make a protein called fibrillin-1 [3]. These protein molecules normally cluster together to form tiny “microfibrils” that give your tissues their structure and resilience [4].

When the FBN1 gene has a mutation (a “misspelling” in the instructions), the body either produces too little fibrillin-1 or produces a version that doesn’t work correctly [5][6]. As a result, the “rubber bands” in the tissues are more prone to stretching or tearing [2].

The Role of TGF-beta

Fibrillin-1 doesn’t just provide structure; it also acts as a “storage locker” for a powerful growth protein called TGF-beta (transforming growth factor-beta) [4][7].

  • Normal Function: Healthy fibrillin-1 holds onto TGF-beta, keeping it inactive until the body needs it [8].
  • In Marfan Syndrome: Because the fibrillin-1 is faulty, it cannot hold onto TGF-beta properly. This leads to an overactivation of TGF-beta [3][2].

This excess of TGF-beta tells the body to grow and change in ways it shouldn’t, contributing to the tall stature, long fingers, and changes in the heart’s blood vessels seen in Marfan syndrome [9][10].

How Marfan Syndrome is Inherited

Marfan syndrome follows a pattern called autosomal dominant inheritance [1].

  • The 50% Rule: Every person has two copies of the FBN1 gene (one from each parent). If one parent has Marfan syndrome, there is a 50% chance in each pregnancy that the child will inherit the mutated gene [1].
  • De Novo (New) Mutations: About 25% to 30% of people with Marfan syndrome are the first in their family to have it [11][12]. This is called a de novo mutation, which happens spontaneously at the time of conception. Once someone has a de novo mutation, they can pass it on to their children following the 50% rule [1].

Why Symptoms Vary (Genotype-Phenotype)

Not all mutations in the FBN1 gene are the same. This helps explain why one person may have very different symptoms than another, even within the same family [13].

Tip: Ask your geneticist or genetic counselor to explain which type of mutation is on your lab report, as this can help connect the science to your actual care plan.

Mutation Type Description Common Clinical Insight
Haploinsufficiency (HI) The body produces only half the amount of normal fibrillin-1 [14]. Sometimes associated with a higher risk of aortic dissection at a younger age [5][15].
Dominant-Negative (DN) The body makes a “bad” protein that interferes with the “good” protein [5]. Often more frequently associated with ectopia lentis (lens dislocation) [5][15].
Neonatal Region Mutations occurring specifically in exons 24–32 [16]. Can lead to “Neonatal Marfan syndrome,” a very severe form that appears at birth [17][18].

Understanding your specific mutation can help your doctors personalize your care and monitoring [13].

Frequently Asked Questions

What is the FBN1 gene and what does it do?
The FBN1 gene provides the instructions for making a protein called fibrillin-1. In Marfan syndrome, a mutation in this gene leads to faulty or insufficient fibrillin-1, which weakens the body's connective tissues and affects how it grows.
Is Marfan syndrome always inherited from a parent?
Not always. While most people inherit Marfan syndrome from a parent, about 25% to 30% of cases are caused by a spontaneous genetic change at conception, known as a de novo mutation.
What are the chances of passing Marfan syndrome to my children?
Because Marfan syndrome follows an autosomal dominant inheritance pattern, a person with the condition has a 50% chance of passing the mutated FBN1 gene to each of their children in every pregnancy.
What does haploinsufficiency mean on my Marfan genetic report?
Haploinsufficiency means your body produces only half the normal amount of the fibrillin-1 protein. This specific mutation type is sometimes associated with a higher risk for aortic issues at a younger age.
What is a dominant-negative mutation in Marfan syndrome?
A dominant-negative mutation means your body makes a faulty fibrillin-1 protein that interferes with the healthy protein. This type of mutation is frequently associated with a higher risk for eye issues, such as lens dislocation.

Questions for Your Doctor

  • • Was my FBN1 mutation inherited, or is it a 'de novo' mutation?
  • • Is my mutation considered 'haploinsufficient' or 'dominant-negative,' and how does that affect my risk for eye or heart issues?
  • • What does my specific genetic result mean for my siblings or future children?
  • • Are there other genes besides FBN1 that you tested for, such as those related to Loeys-Dietz syndrome?
  • • How often should my family members be screened if we haven't found a mutation yet?

Questions for You

  • • Has anyone else in my family ever had a sudden heart problem or eye surgery at a young age?
  • • How do I feel about sharing my genetic results with my relatives?
  • • What are my main concerns or fears when I think about the '50/50' chance of passing this on?

Want personalized information?

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References

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    Clinical Characteristics of Marfan Syndrome in Korea.

    Lim AY, Song JS, Kim EK, et al.

    Korean circulation journal 2016; (46(6)):841-845 doi:10.4070/kcj.2016.46.6.841.

    PMID: 27826344
  2. 2

    Nanoscale Structural Comparison of Fibrillin-1 Microfibrils Isolated from Marfan and Non-Marfan Syndrome Human Aorta.

    Șulea CM, Mártonfalvi Z, Csányi C, et al.

    International journal of molecular sciences 2023; (24(8)) doi:10.3390/ijms24087561.

    PMID: 37108724
  3. 3

    Engineered mutations in fibrillin-1 leading to Marfan syndrome act at the protein, cellular and organismal levels.

    Zeyer KA, Reinhardt DP

    Mutation research. Reviews in mutation research 2015; (765()):7-18.

    PMID: 26281765
  4. 4

    The N-Terminal Region of Fibrillin-1 Mediates a Bipartite Interaction with LTBP1.

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    Structure (London, England : 1993) 2017; (25(8)):1208-1221.e5 doi:10.1016/j.str.2017.06.003.

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    Genotype FBN1/phenotype relationship in a cohort of patients with Marfan syndrome.

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    Clinical genetics 2021; (99(2)):269-280 doi:10.1111/cge.13879.

    PMID: 33174221
  6. 6

    Betaglycan (TGFBR3) up-regulation correlates with increased TGF-β signaling in Marfan patient fibroblasts in vitro.

    Groeneveld ME, Bogunovic N, Musters RJP, et al.

    Cardiovascular pathology : the official journal of the Society for Cardiovascular Pathology 2018; (32()):44-49 doi:10.1016/j.carpath.2017.10.003.

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    Three-generation family with novel contiguous gene deletion on chromosome 2p22 associated with thoracic aortic aneurysm syndrome.

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    American journal of medical genetics. Part A 2018; (176(3)):560-569 doi:10.1002/ajmg.a.38590.

    PMID: 29350460
  8. 8

    Co-existence of Marfan syndrome and systemic sclerosis: A case report and a hypothesis suggesting a common link.

    Yap WF, Chong HC

    International journal of rheumatic diseases 2020; (23(11)):1568-1573 doi:10.1111/1756-185X.13965.

    PMID: 32969582
  9. 9

    Ulnar Artery Aneurysm as a Late Sequela of Marfan Syndrome.

    Goodenough CJ, Afifi RO, Prakash SK, et al.

    The Journal of hand surgery 2020; (45(11)):1090.e1-1090.e5 doi:10.1016/j.jhsa.2020.01.010.

    PMID: 32213296
  10. 10

    Transforming Growth Factor β Receptor Type I Inhibitor, Galunisertib, Has No Beneficial Effects on Aneurysmal Pathological Changes in Marfan Mice.

    Park JH, Kim MS, Ham S, et al.

    Biomolecules & therapeutics 2020; (28(1)):98-103 doi:10.4062/biomolther.2019.042.

    PMID: 31284709
  11. 11

    FBN1 gene mutations in 26 Hungarian patients with suspected Marfan syndrome or related fibrillinopathies.

    Madar L, Szakszon K, Pfliegler G, et al.

    Journal of biotechnology 2019; (301()):105-111 doi:10.1016/j.jbiotec.2019.05.012.

    PMID: 31163209
  12. 12

    Novel Marfan Syndrome-Associated Mutation in the FBN1 Gene Caused by Parental Mosaicism and Leading to Abnormal Limb Patterning.

    Martínez-Quintana E, Caballero-Sánchez N, Rodríguez-González F, et al.

    Molecular syndromology 2017; (8(3)):148-154 doi:10.1159/000467909.

    PMID: 28588436
  13. 13

    Clinical relevance of genotype-phenotype correlations beyond vascular events in a cohort study of 1500 Marfan syndrome patients with FBN1 pathogenic variants.

    Arnaud P, Milleron O, Hanna N, et al.

    Genetics in medicine : official journal of the American College of Medical Genetics 2021; (23(7)):1296-1304 doi:10.1038/s41436-021-01132-x.

    PMID: 33731877
  14. 14

    Marfan syndrome: current perspectives.

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    The application of clinical genetics 2016; (9()):55-65 doi:10.2147/TACG.S96233.

    PMID: 27274304
  15. 15

    Combining clinical examination with exome sequencing for the diagnosis and treatment of Marfan syndrome: a case series of 6 families from China.

    Duan Y, Li P, Ding T, et al.

    Annals of palliative medicine 2021; (10(9)):9953-9962 doi:10.21037/apm-21-2305.

    PMID: 34628919
  16. 16

    Genotype-phenotype spectrum and prognosis of early-onset Marfan syndrome.

    Kemezyte A, Gegieckiene R, Burnyte B

    BMC pediatrics 2023; (23(1)):539 doi:10.1186/s12887-023-04357-8.

    PMID: 37891508
  17. 17

    Early-onset Marfan syndrome with a novel missense mutation: A case report.

    Soma K, Kitagawa Y, Toki T, et al.

    Journal of cardiology cases 2023; (27(6)):283-286 doi:10.1016/j.jccase.2023.02.019.

    PMID: 37283908
  18. 18

    Variable severity of cardiovascular phenotypes in patients with an early-onset form of Marfan syndrome harboring FBN1 mutations in exons 24-32.

    Maeda J, Kosaki K, Shiono J, et al.

    Heart and vessels 2016; (31(10)):1717-23 doi:10.1007/s00380-016-0793-2.

    PMID: 26796135

This page explains the genetics and biology of Marfan syndrome for educational purposes. A genetic counselor or medical geneticist is the best source to interpret your specific genetic test results and family risks.

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