The C9orf72 gene helps nerve cells and immune cells manage waste and keep the cell’s internal transport system running smoothly. If it does not work properly, cells can become stressed, and in some people a large repeat expansion in this gene is linked to amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Some people first learn about this gene when a family has several relatives with ALS or FTD. It is one of the best known genetic causes of inherited ALS and FTD.
What is a gene?
A gene is a stretch of DNA that holds instructions your cells use to make molecules or guide processes throughout the body. Some genes provide the directions for producing proteins, which are the parts of cells that do much of the work. Others mainly regulate when certain processes happen, where they take place, and how active they are. Taken together, genes affect how the body grows and works, and they can also influence how you respond to food, stress, and medicines. For a deeper look at this subject, more information is available in LearnHub.
Overview
C9orf72Gene function
What if the gene works
The C9ORF72 gene helps cells move and recycle worn out materials. It also supports immune cell activity and may help nerve cells stay healthy.
Risk
What if the gene does not work
Some C9ORF72 gene variants can cause frontotemporal dementia, amyotrophic lateral sclerosis, or both. Effects may range from milder thinking or behavior changes to more severe weakness, and the age at onset can vary.
Treatment
What does that mean for your treatment
For the C9orf72 gene, no gene specific treatment or management approach is currently established in clinical guidelines. C9orf72 linked ALS and frontotemporal dementia are active areas of research, and therapies that aim to lower the effects of the repeat expansion are being studied, but they are not standard treatment yet.
Conditions associated with C9orf72
Gene function
What if the gene works
Inside your cells, materials are constantly being moved, sorted, and recycled. The C9orf72 gene helps keep these everyday cleanup and transport tasks running smoothly. Understanding what the C9orf72 gene does in your cells makes its role in routine cell maintenance easier to picture.
The C9orf72 gene helps guide autophagy, a cleanup process that delivers worn out proteins and damaged cell parts for breakdown. This lets cells clear space and reuse some of the building blocks.
Its protein helps small membrane packages carry material between cell compartments. This keeps sorting and cleanup pathways connected and orderly.
C9orf72 supports lysosomes, the cell's cleanup compartments. These compartments break down old material so useful parts can be recycled.
What is a variant?
A genetic variant is a minor difference in the DNA sequence within a gene. These differences are common and are part of normal human variation, including traits such as appearance, metabolism, and the way the body responds to environmental influences. Many do not have any noticeable effect and simply represent natural genetic diversity. In some cases, though, a variant can change how a gene works more substantially and may contribute to, or directly cause, a genetic condition.
Genetic variants
What if the gene does not work
Many changes in the C9orf72 gene are mild, but a C9orf72 repeat expansion can have a much stronger effect. It may lower the amount of normal protein made and also produce toxic RNA and abnormal repeat proteins that interfere with nerve cell function. Larger or more disruptive expansions often have greater functional impact, though in C9orf72 related ALS and frontotemporal dementia, age at onset and symptom severity still vary.
How variants are linked to conditions
Pathogenic repeat expansions in the C9orf72 gene are a well established cause of some cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). In families with a C9orf72 gene linked to ALS and frontotemporal dementia, some people develop ALS, some develop FTD, and some have features of both. This finding is one of the most common inherited genetic causes identified in the ALS and FTD spectrum.
A variant is not necessarily a diagnosis
Variants in genes are a routine part of human biology and are widely found across the general population. Most do not directly affect health and simply reflect natural human variation. For many genes, having a variant associated with a condition points to a possible link rather than a confirmed diagnosis, particularly when several genes and environmental influences play a role. In certain situations, though, one well-characterized variant in a particular gene is enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For C9orf72, risk is driven mainly by having a harmful repeat expansion, and the chance of developing related nerve or memory problems rises with age. Family history can also matter. There is not enough evidence to say that lifestyle changes lower this inherited risk.
Inheritance of C9orf72 variants
For the best known C9orf72-related conditions, including some forms of ALS and frontotemporal dementia, C9orf72 inheritance is autosomal dominant. This means a person with the disease linked expansion in one copy of the C9orf72 gene can pass it to each child, with a 50% chance in each pregnancy. Men and women can inherit and pass on the expansion equally. Even within the same family, the age symptoms begin and the pattern of symptoms can vary.
What does my C9orf72 result mean for my family?
For a disease-causing C9orf72 repeat expansion, close relatives can also carry the same change. In families where it is passed down, each child, brother, sister, or parent has a 1 in 2 chance of having it. Some people who carry the expansion develop nerve or thinking problems, while others may stay well for many years, so the family impact can vary.
Genetic information
Genetic testing
How you find out about variants
To look for changes in the C9orf72 gene, labs usually test a blood or saliva sample with special methods that measure whether its repeated DNA section is in the usual range or expanded. C9orf72 genetic testing may also check for a known family variant when one has already been identified.
When should I consider getting a genetic test?
Consider genetic testing for the C9ORF72 gene if you or close relatives have ALS or a form of dementia that mainly affects behavior and language, especially when several family members are affected. Testing can help show whether an inherited change in this gene is the cause.
A genetic result is only one part of your health story
A genetic result can be informative, but how much it reveals depends on the condition and on the kind of variant involved. Over time, many factors, including lifestyle, environment, age, and medical history, influence how the body functions. For some conditions, especially those shaped by many genes, genetic information offers context rather than certainty and is best interpreted alongside other parts of care. In other situations, a genetic result may give a clear answer. In areas like medication response, genetic results can also help put individual experiences into context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how people respond to medicines. This helps explain why the same treatment works well for one person, has less effect in another, or causes more side effects in someone else. These differences are common and often reflect how the body absorbs, breaks down, or responds to a drug, which can influence both benefit and sensitivity.
What is Pharmacogenetics?
Pharmacogenetics examines how genetic variation can affect the way a person responds to medications. It studies the relationship between genes and drugs to help explain why the same treatment may work differently from one person to another. With many medicines, genes can influence both how strongly a drug works and how the body processes it. This understanding can help support treatment decisions that are more informed and more individualized. You can read more about this topic in the LearnHub.
Drugs influenced by the C9orf72 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in guiding medication choice or dosing, so any concerns about medicines, side effects, or changes in your health are best discussed with your doctor.
History
For years, families affected by amyotrophic lateral sclerosis and frontotemporal dementia were known to share an inherited change on chromosome 9, but the exact cause remained unclear. In 2011, researchers identified an unusual repeated DNA sequence in the C9orf72 gene, a finding that helped explain many inherited cases of both conditions. From these first observations, research expanded steadily. This discovery was a major turning point because it linked two illnesses once studied more separately and gave families a clearer genetic answer. It also reshaped research on neurodegenerative disease by showing that repeated stretches of DNA can play a central role. Today, the C9orf72 gene remains one of the most studied genes in ALS and frontotemporal dementia history.