Health condition
Marfan syndrome genetics
Marfan syndrome is caused by variants in the FBN1 gene affecting the connective tissue protein fibrillin-1 - genetics now sits at the heart of diagnosis, family testing and separating Marfan from its lookalike syndromes.
Why trust this guide
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Editorial team
Written by our editorial team from the UK sources listed on each page.
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Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
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Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
Which gene and test confirm it, who should be tested in the family, and which specialist to see.
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Caused by FBN1 variants; autosomal dominant - each child of an affected parent has a 50% chance; about a quarter of cases are new mutations
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Diagnosis uses the revised Ghent criteria: aortic root measurement, lens dislocation, systemic features and FBN1 result together
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Genetic testing distinguishes Marfan from Loeys-Dietz (TGFBR1/2 and related genes) and vascular EDS (COL3A1) - conditions with different surveillance thresholds
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A confirmed variant enables cascade testing of relatives, who enter aortic surveillance early
Understanding the condition
What it is and what happens next.
What causes it, how it is confirmed, and the testing and specialist routes available in the UK.
What it is and how it presents
Fibrillin-1 is scaffolding for elastic tissues and a regulator of growth signalling, which is why FBN1 variants stretch their effects across the skeleton (tall stature, long limbs and fingers, chest wall deformity), the eye (upward lens dislocation) and - decisively for prognosis - the aorta, which dilates at the root and can dissect. Not every FBN1 variant causes full Marfan syndrome, and not every marfanoid person has an FBN1 variant, which is exactly why diagnosis pairs genetics with clinical criteria.
Testing, surveillance and specialist care
Modern assessment runs an aortopathy gene panel rather than FBN1 alone, because the management stakes of distinguishing Marfan from Loeys-Dietz or vascular EDS are high - surgical thresholds and imaging schedules differ. A confirmed variant converts family screening from serial echocardiograms for everyone into a single definitive test per relative, organised with genetic counselling. NHS clinical genetics services carry some of the longest waits in the health service, often many months for a first appointment, whereas private genetic testing and a specialist review can typically be arranged within around two weeks.
Seeing a specialist
Who to see, and how quickly you can be seen.
The specialist for this condition is usually a clinical geneticist working with a cardiologist. Your GP can refer you on the NHS, or you can arrange a private consultation directly.
A quiet reminder
This guide is for information, not medical advice.
Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any emergency symptoms.
Frequently asked
Common questions about Marfan syndrome genetics.
Quick, plain-English answers to what people ask us most.
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What is the genetic basis of Marfan syndrome?
Marfan syndrome is caused by mutations in the FBN1 gene, which produces fibrillin-1, a protein essential for the structural integrity of connective tissue throughout the body. These mutations weaken connective tissue, affecting the heart, blood vessels, eyes, and skeleton.
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How is Marfan syndrome inherited?
It's inherited in an autosomal dominant pattern, meaning a person with Marfan syndrome has a 50% chance of passing the condition to each of their children. Around a quarter of cases arise from a new (de novo) mutation with no family history.
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Does everyone with the same Marfan mutation have the same symptoms?
No, there's considerable variation in how severely the condition affects different people, even within the same family sharing an identical mutation, due to other genetic and environmental factors that aren't yet fully understood. This variability makes individualised assessment and monitoring important for everyone diagnosed.
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Is genetic testing for Marfan syndrome always needed for diagnosis?
Not always, as diagnosis can sometimes be made based on characteristic clinical features alone using established diagnostic criteria, but genetic testing can help confirm uncertain cases and is particularly useful for testing family members who might be at risk. Genetic counselling helps explain the role and limitations of genetic testing in your specific situation.
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Can Marfan syndrome genetics predict how severe the condition will be?
To some extent certain specific mutations are associated with more or less severe disease patterns on average, but predicting individual severity remains imprecise, and regular clinical monitoring remains essential regardless of the specific genetic finding. Research continues to refine our understanding of these genotype-phenotype relationships.
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How does genetic testing for Marfan syndrome work?
It typically involves a blood test analysing the FBN1 gene for mutations, sometimes alongside testing for other genes that can cause similar conditions if the diagnosis is uncertain. Results are interpreted by a clinical geneticist in the context of your specific clinical features and family history.
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How does a Marfan syndrome diagnosis affect family planning decisions?
Given the 50% inheritance risk with each pregnancy, genetic counselling can help discuss options including prenatal testing or preimplantation genetic testing for those wanting to reduce the chance of passing on the condition. These are personal decisions best made with full information from a genetics specialist.
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Marfan syndrome vs other genetic connective tissue disorders — what's the difference?
Marfan syndrome is specifically caused by FBN1 mutations, while related conditions such as Loeys-Dietz syndrome and vascular Ehlers-Danlos syndrome are caused by different genes and can have overlapping but distinct clinical features, particularly regarding aortic disease risk and progression. Genetic testing helps distinguish between these related conditions when clinical features overlap, which is important because management approaches, including aortic surgery timing, can differ.
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If genetic testing is negative but I have Marfan-like features, what does that mean?
A negative genetic test doesn't necessarily rule out Marfan syndrome, since not all mutations are detectable with current testing methods, and clinical diagnosis based on established criteria remains valid even without a confirmed genetic finding. Your geneticist will interpret a negative result in the full context of your clinical presentation.
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When should I see a specialist about Marfan syndrome genetics, and how quickly can I be seen privately?
If you have features suggestive of Marfan syndrome or a relevant family history, clinical genetics assessment is worthwhile. Private genetics consultations can typically be arranged within about two weeks, considerably faster than standard NHS waiting times.