The CD55 gene helps protect your own cells from part of the immune system called complement, which is meant to attack germs. This gene plays an important role in keeping that response under control so blood cells and the lining of the gut are not harmed. When the gene does not work properly, uncontrolled complement activity can lead to a rare inherited condition with bowel inflammation, protein loss, swelling, blood clots, and low blood counts.
What is a gene?
A gene is a section of DNA that holds instructions your cells use to make molecules or regulate processes in the body. Some genes provide the information needed to produce proteins, the parts of cells that carry out much of their work. Other genes mainly direct when certain processes happen, where they happen, and how strongly they take place. Together, genes influence how the body develops and functions, and they can shape how you respond to food, stress, and medications. To explore this topic further, you can find more in the LearnHub.
Overview
CD55Gene function
What if the gene works
The CD55 gene helps make a cell surface protein that protects your own cells from a part of the immune system called complement. This helps limit unwanted inflammation and cell damage.
Risk
What if the gene does not work
More disruptive variants in the CD55 gene can cause loss of protein from the gut, chronic diarrhea, swelling, blood clots, and repeated infections, while milder variants may lead to later onset or fewer features.
Treatment
What does that mean for your treatment
For people with pathogenic loss-of-function variants in the CD55 gene, treatment often centers on complement-blocking therapy, most commonly eculizumab. This gene-specific approach can improve protein loss from the gut and may reduce clotting-related complications, so it can strongly influence drug choice and long term management.
Conditions associated with CD55
Gene function
What if the gene works
Your immune system uses the CD55 gene to keep one of its defense pathways under control. It makes a cell surface protein that acts like a brake on complement, a group of blood proteins that helps mark targets for attack. This allows normal immune defense while helping protect your own cells.
CD55 sits on the outer surface of many cells and slows complement, a protein system that helps the immune system react to threats. It does this by breaking apart complement enzyme teams before they can keep the signal going.
By calming complement on the cell surface, the CD55 gene helps healthy blood cells and body tissues avoid being caught up in everyday immune activity. This is a central part of what the CD55 gene does in the immune system.
CD55 helps keep immune tagging and attack more targeted rather than spreading too far. This supports a steadier inflammatory response and helps the body clear microbes while limiting spillover onto nearby cells.
What is a variant?
Genetic variants are small differences in a gene’s DNA sequence. They are common and help explain normal differences between people, such as appearance, metabolism, and the way the body responds to environmental influences. Many do not have any noticeable effect and are simply part of natural genetic variation. Sometimes, though, a variant changes how a gene works more significantly and can contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
CD55 gene variants can reduce cell surface protein levels or weaken the protein's ability to shut down complement activity. Some changes create a shortened or unstable protein that is broken down before it can work. Others alter key regions needed for proper folding or binding, leaving partial activity. This effect ranges from mild to near-complete loss of function, and more severe variants are often linked to earlier and more pronounced CHAPLE syndrome features.
How variants are linked to conditions
Pathogenic variants in both copies of the CD55 gene cause CD55 deficiency, also called CHAPLE syndrome. Among conditions linked to CD55 gene variants, this is the main well-established one. People with this inherited condition often have chronic diarrhea, protein-losing enteropathy, low blood protein, swelling, poor growth, and a higher chance of blood clots.
A variant is not necessarily a diagnosis
Variants in genes are a usual part of human biology and are common in the general population. Most do not have a direct effect on health and simply reflect natural human diversity. For many genes, carrying a variant connected with a condition indicates a possible association rather than a definite diagnosis, especially when several genes and environmental factors are involved. In some situations, however, a single well-characterized variant in a specific gene can be enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For CD55, risk is mainly shaped by genetics rather than lifestyle. A person’s chance of having the related condition is much higher if they inherit harmful changes in both copies of the CD55 gene, and family history or parents who are related by blood can raise that chance.
Inheritance of CD55 variants
CD55-related conditions are inherited in an autosomal recessive pattern. This means a child usually develops the condition only after inheriting two altered copies of the CD55 gene, one from each parent. Parents who carry one altered copy are typically called carriers and usually do not have the condition themselves. In practical terms, how CD55 gene variants are inherited often means brothers and sisters can share the same risk, while parents may be unaffected carriers. Because the CD55 gene is on chromosome 1, an autosome, this inheritance pattern is the same for females and males.
What does my CD55 result mean for my family?
For families affected by CD55-related disease, close relatives may also carry the gene change. Brothers and sisters can sometimes have the same condition or be carriers even if they feel well, and parents are usually healthy carriers. Because of this, family members may want to talk with a genetics professional about whether testing would be helpful for them.
Genetic information
Genetic testing
How you find out about variants
Genetic testing for CD55 variants uses a blood sample or cheek swab to read the DNA in the CD55 gene and look for changes. The lab compares your sequence with the usual version to see whether a variant is present, which can help confirm or rule out a CD55-related condition.
When should I consider getting a genetic test?
Consider CD55 genetic testing if someone has severe ongoing protein loss from the gut, repeated blood clots, swelling, and low blood protein levels starting in childhood, or if a close family member has a confirmed CD55-related condition. A positive result can help confirm the diagnosis.
A genetic result is only one part of your health story
A genetic finding can provide useful insight, but how much it reveals depends on the condition and 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 adds context rather than certainty and is best understood together with other parts of care. In other situations, a genetic result may offer a clear answer. In areas such as 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. A treatment that works well for one person may work less well for another, or may cause more side effects, because the body can absorb, break down, or respond to drugs in different ways. These inherited differences are common and are one reason medication response is not the same for everyone. In some situations, genetic test results can help explain why a medicine seems more effective or why someone is more sensitive to it.
What is Pharmacogenetics?
Pharmacogenetics looks at how genetic differences can shape the way a person responds to medications. It examines links between genes and drugs to help explain why the same treatment can work differently from one person to another. For many medicines, genes may affect how strongly a drug works or how the body handles it. This information can support more informed and more individualized treatment decisions. You can read more about this topic in the LearnHub.
Drugs influenced by the CD55 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in predicting how most medicines will work or what side effects they may cause. General health concerns or questions about medication response are best discussed with your doctor. In rare CD55-related illness, specialists may use the genetic finding as part of discussions about complement-blocking treatment, but this is not a routine drug-response result for most people.
History
CD55 entered medical research through studies of the complement system, a part of the immune system that can damage cells if not tightly controlled. In the 1980s, researchers identified the protein known as decay accelerating factor on blood cells and other tissues. Building on this early work, scientists linked loss of this surface protein to paroxysmal nocturnal hemoglobinuria, which helped clarify why blood cells in that condition break down more easily. As gene mapping improved in the late 20th century, the CD55 gene was identified and its place in regulating complement became clearer. Its history is mainly scientific rather than public, but it has been important in shaping modern understanding of immune balance and rare blood conditions.