rare-and-clear

FBN1 fibrillin 1

Also known as: asprosin, Marfan syndrome, MASS, OCTD, SGS.

Approximate pronunciation (generated from the name, not a recording):

What this gene does

The FBN1 gene provides instructions for making a large protein called fibrillin-1. This protein is transported out of cells into the extracellular matrix, which is an intricate lattice of proteins and other molecules that forms in the spaces between cells. In the extracellular matrix, fibrillin-1 proteins bind to each other and to other proteins to form threadlike filaments called microfibrils, which are organized into a network. This microfibrillar network acts as a platform or scaffold for the assembly of elastic fibers, which enable the skin, ligaments, and blood vessels to stretch. The microfibrillar network also provides support to the bones and to the tissues that support the nerves, muscles, and lenses of the eyes.

As part of the microfibrillar network, fibrillin-1 also regulates certain growth factor proteins. Growth factors are important proteins that help regulate cell processes such as the growth and division (proliferation) of cells, the process by which cells mature to carry out specific functions (differentiation), cell movement, and the self-destruction of cells (apoptosis). A particular growth factor called transforming growth factor beta (TGF-β) is stored within the microfibrillar network. When it is stored, TGF-β is turned off. Once it is released from the network, TGF-β is turned on and can activate important signaling pathways, including those involved in bone formation. By helping to regulate the availability of TGF-β, fibrillin-1 also helps regulate its activity.

Source: MedlinePlus Genetics (reviewed 2026-04; source updated 2026-04-01).

Marfan syndrome

Approximate pronunciation (generated from the name, not a recording):

  • Marfan syndrome marfan syndrome

Also known as: MFS, Marfan's syndrome.

What is Marfan syndrome?

Marfan syndrome is a disorder that affects the connective tissue in many parts of the body. Connective tissue provides strength and flexibility to structures such as bones, ligaments, muscles, blood vessels, and heart valves. The signs and symptoms of Marfan syndrome vary widely in severity, timing of onset, and rate of progression.

Because connective tissue is found throughout the body, Marfan syndrome can affect many systems, often causing abnormalities in the heart, blood vessels, eyes, bones, and joints. The two primary features of Marfan syndrome are vision problems caused by a dislocated lens (ectopia lentis) in one or both eyes and defects in the large blood vessel that distributes blood from the heart to the rest of the body (the aorta). The aorta can weaken and stretch, which may lead to a bulge in the blood vessel wall (an aneurysm). Stretching of the aorta may cause the aortic valve to leak, which can lead to a sudden tearing of the layers in the aorta wall (aortic dissection). Aortic aneurysm and dissection can be life threatening.

Many people with Marfan syndrome have additional heart problems including a leak in the valve that connects two of the four chambers of the heart (mitral valve prolapse) or the valve that regulates blood flow from the heart into the aorta (aortic valve regurgitation). Leaks in these valves can cause shortness of breath, fatigue, and an irregular heartbeat felt as skipped or extra beats (palpitations).

Individuals with Marfan syndrome are usually tall and slender, have elongated fingers and toes (arachnodactyly), loose joints, and have an arm span that exceeds their body height. Other common features include a long and narrow face, crowded teeth, an abnormal curvature of the spine (scoliosis or kyphosis), stretch marks (striae) not related to weight gain or loss, and either a sunken chest (pectus excavatum) or a protruding chest (pectus carinatum). Some individuals develop an abnormal accumulation of air in the chest cavity that can result in the collapse of a lung (spontaneous pneumothorax). A membrane called the dura, which surrounds the brain and spinal cord, can be abnormally enlarged (dural ectasia) in people with Marfan syndrome. Dural ectasia can cause pain in the back, abdomen, legs, or head. Most individuals with Marfan syndrome have some degree of nearsightedness (myopia). Clouding of the lens (cataract) may occur in mid-adulthood, and increased pressure within the eye (glaucoma) occurs more frequently in people with Marfan syndrome than in those without the condition.

The features of Marfan syndrome can become apparent anytime between infancy and adulthood. Depending on the onset and severity of signs and symptoms, Marfan syndrome can be fatal early in life; however, with proper treatment, many affected individuals have normal lifespans.

Source: MedlinePlus Genetics (reviewed 2012-03; source updated 2023-11-08).

How it is inherited

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder.

At least 25 percent of Marfan syndrome cases result from a new mutation in the FBN1 gene. These cases occur in people with no history of the disorder in their family.

Source: MedlinePlus Genetics (reviewed 2012-03; source updated 2023-11-08).

How common it is

MedlinePlus Genetics Frequency

The incidence of Marfan syndrome is approximately 1 in 5,000 worldwide.

Source: MedlinePlus Genetics (reviewed 2012-03; source updated 2023-11-08).

Research studies

10 studies recruiting people with Marfan syndrome. Showing the first 5 of 10.

See all recruiting studies on ClinicalTrials.gov.

Source: ClinicalTrials.gov (retrieved 2026-10-04).

Family and care

What a diagnosis can mean for a family, and what to ask. This guidance is general, not specific to one gene.

What is a genetic consultation?

A genetic consultation is a health service that provides information and support to people who have, or may be at risk for, genetic conditions. During a consultation, a genetics professional meets with an individual or family to discuss genetic risks or to diagnose, confirm, or rule out a genetic condition.

Genetics professionals include medical geneticists (doctors who specialize in genetics) and genetic counselors (certified healthcare workers with experience in medical genetics and counseling). Other healthcare professionals such as nurses, psychologists, and social workers trained in genetics can also provide genetic consultations.

Consultations usually take place in a doctor’s office, hospital, genetics center, or other type of medical center. These meetings are most often in-person visits with individuals or families, but they are occasionally conducted in a group. Additionally, genetic consultations may be carried out using telemedicine (also known as telehealth), in which the meeting is done from a distance using computers, cameras, videoconferencing tools, or the telephone.

Source: MedlinePlus Genetics.

Why might someone have a genetic consultation?

Individuals or families who are concerned about an inherited condition may benefit from a genetic consultation. The reasons that a person might be referred to a genetic counselor, medical geneticist, or other genetics professional include:

A personal or family history of a genetic condition, birth defect, chromosomal disorder, or hereditary cancer.

Two or more pregnancy losses (miscarriages), a stillbirth, or a baby who died.

A child with a known inherited disorder, a birth defect, intellectual disability, or developmental delay.

A woman who is pregnant or plans to become pregnant at or after age 35. (Some chromosomal disorders occur more frequently in children born to older women.)

Abnormal test results that suggest a genetic or chromosomal condition.

An increased risk of developing or passing on a particular genetic disorder on the basis of a person’s ethnic background.

People related by blood (for example, cousins) who plan to have children together. (A child whose parents are related may be at an increased risk of inheriting certain genetic disorders.)

A person received results from direct-to-consumer genetic testing and they want to discuss the implications of the results.

A genetic consultation is also an important part of the decision-making process for genetic testing. A visit with a genetics professional may be helpful even if testing is not available for a specific condition, however.

Source: MedlinePlus Genetics.

What happens during a genetic consultation?

A genetic consultation provides information, offers support, and addresses a patient’s specific questions and concerns. To help determine whether a condition has a genetic component, a genetics professional asks about a person’s medical history and takes a detailed family health history (a record of health information about a person's immediate and extended family). The genetics professional may also perform a physical examination and recommend appropriate medical tests.

If a person is diagnosed with a genetic condition, the genetics professional provides information about the diagnosis, how the condition is inherited, the chance of passing the condition to future generations, and the options for testing and treatment.

During a consultation, a genetics professional will:

Interpret and communicate complex medical information.

Help each person make informed, independent decisions about their health care and reproductive options.

Respect each person’s individual beliefs, traditions, and feelings.

A genetics professional will NOT:

Tell a person which decision to make.

Coerce a couple about whether or not to have children.

Recommend that a woman continue or end a pregnancy.

Tell someone whether to undergo testing for a genetic disorder.

Source: MedlinePlus Genetics.

What is genetic counseling?

The goal of genetic counseling is to help you learn more about the causes of genetic conditions and how they affect you.

Genetic counselors can: Review your family and medical histories; Explain how genetic conditions are passed down through families; Figure out if you or your family members are at risk for disease; Find and give you information about genetic conditions; Offer guidance to help you make informed choices or life plans; Provide information about testing options and help you decide what is best for you and your family; Help you find referrals to medical specialists, advocacy and support networks, and other resources.

Source: National Society of Genetic Counselors and Genetic Alliance (CC BY; published 2008).

Where to go next

Words you may meet

Some technical words appear in the sections above and in the details below. Here is what they mean, in words from a public genetics glossary.

Gene
The gene is considered the basic unit of inheritance. Genes are passed from parents to offspring and contain the information needed to specify physical and biological traits. Most genes code for specific proteins, or segments of proteins, which have differing functions within the body. Humans have approximately 20,000 protein-coding genes. NHGRI Talking Glossary of Genomic and Genetic Terms
Chromosome
Chromosomes are threadlike structures made of protein and a single molecule of DNA that serve to carry the genomic information from cell to cell. In plants and animals (including humans), chromosomes reside in the nucleus of cells. Humans have 22 pairs of numbered chromosomes (autosomes) and one pair of sex chromosomes (XX or XY), for a total of 46. Each pair contains two chromosomes, one coming from each parent, which means that children inherit half of their chromosomes from their mother and half from their father. Chromosomes can be seen through a microscope when the nucleus dissolves during cell division. NHGRI Talking Glossary of Genomic and Genetic Terms
Autosomal Recessive Disorder
Autosomal recessive is a pattern of inheritance characteristic of some genetic disorders. “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Recessive” means that two copies of the mutated gene (one from each parent) are required to cause the disorder. In a family where both parents are carriers and do not have the disease, roughly a quarter of their children will inherit two disease-causing alleles and have the disease. By contrast, an autosomal dominant disorder requires only a single copy of the mutated gene from one parent to cause the disorder. Sickle cell anemia is an example of an autosomal recessive genetic disorder. NHGRI Talking Glossary of Genomic and Genetic Terms
Autosomal Dominant Disorder
Autosomal dominant is a pattern of inheritance characteristic of some genetic disorders. “Autosomal” means that the gene in question is located on one of the numbered, or non-sex, chromosomes. “Dominant” means that a single copy of the mutated gene (from one parent) is enough to cause the disorder. A child of a person affected by an autosomal dominant condition has a 50% chance of being affected by that condition via inheritance of a dominant allele. By contrast, an autosomal recessive disorder requires two copies of the mutated gene (one from each parent) to cause the disorder. Huntington’s disease is an example of an autosomal dominant genetic disorder. NHGRI Talking Glossary of Genomic and Genetic Terms
Mitochondrial DNA
Mitochondrial DNA is the circular chromosome found inside the cellular organelles called mitochondria. Located in the cytoplasm, mitochondria are the site of the cell’s energy production and other metabolic functions. Offspring inherit mitochondria — and as a result mitochondrial DNA — from their mother. NHGRI Talking Glossary of Genomic and Genetic Terms
Genetic Imprinting
Genomic imprinting is the process by which only one copy of a gene in an individual (either from their mother or their father) is expressed, while the other copy is suppressed. Unlike genomic mutations that can affect the ability of inherited genes to be expressed, genomic imprinting does not affect the DNA sequence itself. Instead, gene expression is silenced by the epigenetic addition of chemical tags to the DNA during egg or sperm formation. Epigenetic tags on imprinted genes usually stay in place for the life of the individual. NHGRI Talking Glossary of Genomic and Genetic Terms
Protein
Proteins are large, complex molecules that play many important roles in the body. They are critical to most of the work done by cells and are required for the structure, function and regulation of the body’s tissues and organs. A protein is made up of one or more long, folded chains of amino acids (each called a polypeptide), whose sequences are determined by the DNA sequence of the protein-encoding gene. NHGRI Talking Glossary of Genomic and Genetic Terms
Mutation
A mutation is a change in the DNA sequence of an organism. Mutations can result from errors in DNA replication during cell division, exposure to mutagens or a viral infection. Germline mutations (that occur in eggs and sperm) can be passed on to offspring, while somatic mutations (that occur in body cells) are not passed on. NHGRI Talking Glossary of Genomic and Genetic Terms
Pathogenic Variant
A pathogenic variant is a genomic variant that may increase a person’s risk of developing a condition, disorder or disease. In many cases, carrying a pathogenic variant does not guarantee that a person will develop the specific condition but increases the risk for it. Pathogenic variants can be inherited from a parent or can occur spontaneously due to factors such as environmental exposure and aging. NHGRI Talking Glossary of Genomic and Genetic Terms
Genetic Testing
Genetic testing is the use of a laboratory test to examine an individual’s DNA for variations, typically performed in the context of medical care, ancestry studies or forensics. In a medical setting, the results of a genetic test can be used to confirm or rule out a suspected genetic disease. Results may also be used to determine the likelihood of parents passing on a genetic mutation to their offspring. Genetic testing may be performed prenatally or after birth. Genetic testing is also used to study the genomes of tumors in cancer cases. NHGRI Talking Glossary of Genomic and Genetic Terms
Carrier
A carrier, as related to genetics, is an individual who “carries” and can pass on to its offspring a genomic variant (allele) associated with a disease (or trait) that is inherited in an autosomal recessive or sex-linked manner, and who does not show symptoms of that disease (or features of that trait). The carrier has inherited the variant allele from one parent and a normal allele from the other parent. Any offspring of carriers is at risk of inheriting a variant allele from their parents, which would result in that child having the disease (or trait). NHGRI Talking Glossary of Genomic and Genetic Terms
Allele
An allele is one of two or more versions of DNA sequence (a single base or a segment of bases) at a given genomic location. An individual inherits two alleles, one from each parent, for any given genomic location where such variation exists. If the two alleles are the same, the individual is homozygous for that allele. If the alleles are different, the individual is heterozygous. NHGRI Talking Glossary of Genomic and Genetic Terms
Mendelian Inheritance
Mendelian inheritance refers to certain patterns of how traits are passed from parents to offspring. These general patterns were established by the Austrian monk Gregor Mendel, who performed thousands of experiments with pea plants in the 19th century. Mendel’s discoveries of how traits (such as color and shape) are passed down from one generation to the next introduced the concept of dominant and recessive modes of inheritance. NHGRI Talking Glossary of Genomic and Genetic Terms
Details you may see on a test report

These names and numbers are the technical ones doctors and labs use. You do not need to memorize them.

Location

This is where the gene sits on its chromosome, so you can match it to coordinates on a test report.

15q21.1 · GRCh38 chr15:48,408,016–48,645,791

Chromosome 15 ideogram with band 15q21.1 highlighted A simplified map of chromosome 15; the highlighted band marks where the gene sits.

Open in Ensembl (primary) or UCSC Genome Browser (secondary).

Source: HGNC (HGNC:3603).

Recommended transcript

This is the reference transcript labs use when they report a change in this gene.

MANE Select
NM_000138.5 (RefSeq) / ENST00000316623.10 (Ensembl)

Source: NCBI MANE.

Protein domains

These are the working parts of the protein, with the amino-acid positions each one covers.

  • EGF-like domain — amino acids 84–112, 118–146, 146–178, 246–287, 288–329, 452–489, 490–529, 530–571, 572–612, 613–653, 723–764, 765–806, 807–846, 910–951, 1028–1069, 1070–1112, 1113–1154, 1155–1196, 1200–1237, 1238–1279, 1280–1321, 1322–1362, 1363–1403, 1404–1445, 1446–1486, 1487–1527, 1606–1647, 1648–1688, 1766–1807, 1808–1848, 1849–1890, 1891–1929, 1930–1972, 1973–2012, 2013–2054, 2127–2165, 2166–2205, 2209–2246, 2250–2290, 2291–2332, 2402–2443, 2447–2484, 2485–2523, 2524–2566, 2567–2606, 2607–2647, 2651–2687
  • EGF-like calcium-binding domain — amino acids 246–287, 288–329, 451–489, 490–529, 530–571, 572–612, 613–653, 723–764, 765–806, 807–846, 910–951, 1028–1069, 1070–1112, 1113–1154, 1155–1196, 1197–1237, 1238–1279, 1280–1321, 1322–1362, 1363–1403, 1404–1445, 1446–1486, 1487–1527, 1606–1647, 1648–1688, 1766–1807, 1808–1848, 1849–1890, 1891–1929, 1930–1972, 1973–2012, 2013–2054, 2127–2165, 2166–2205, 2206–2246, 2247–2290, 2291–2332, 2402–2443, 2444–2484, 2485–2523, 2524–2566, 2567–2606, 2607–2647, 2648–2687
  • TB domain — amino acids 184–228, 334–389, 659–711, 851–891, 956–1008, 1532–1589, 1693–1748, 2059–2111, 2337–2390
  • NELL2-like, EGF domain — amino acids 1367–1402
  • Complement Clr-like EGF domain — amino acids 593–616, 787–810, 1426–1449, 1953–1976, 2547–2570
  • Fibrillin 1, unique N-terminal domain — amino acids 48–82
  • Fibrillin, first EGF domain — amino acids 89–110
  • NOTCH1, EGF-like calcium-binding domain — amino acids 246–286, 288–328, 451–486, 490–528, 530–570, 723–763, 910–944, 1028–1068, 1070–1103, 1113–1153, 1155–1192, 1238–1278, 1280–1320, 1322–1361, 1487–1525, 1606–1646, 1648–1687, 1766–1802, 1808–1845, 1849–1889, 1891–1921, 2013–2053, 2127–2162, 2166–2200, 2206–2245, 2247–2289, 2291–2331, 2402–2442, 2444–2483, 2485–2522, 2607–2641, 2648–2679

Source: InterPro (UniProt P35555).

Protein structure

This lets you look at the protein's 3D shape if you want to.

View the predicted structure in AlphaFold, or search the PDB for solved structures.

Source: UniProt (P35555).

Reported gene variants

ClinVar collects gene variants people have reported; it is a place to search, not a list on this page.

This page does not list individual variants. Search ClinVar for FBN1 instead.

Source: ClinVar.

What this page is not

This page is for education only. It is not medical advice, and it is not a diagnosis or a treatment plan. Talk with a doctor or a genetic counselor about your family's situation.