The CTPS1 gene helps cells make a key building block needed to copy genetic material, especially when white blood cells need to multiply. This gene plays an important role in helping T cells and B cells expand during an infection. If the CTPS1 gene does not work properly, these immune cells may not grow well, which can lead to repeated or unusually severe infections, often starting in childhood. Rare harmful variants in the CTPS1 gene cause an inherited immune deficiency.
What is a gene?
Genes are stretches of DNA that carry instructions your cells use to make molecules or direct activities in the body. Some genes contain the code for proteins, the parts of cells that do much of the work. Other genes 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 influence how you respond to food, stress, and medicines. More information on this topic is available in the LearnHub.
Overview
CTPS1Gene function
What if the gene works
The CTPS1 gene helps immune cells make a building block called CTP, which is needed for DNA and RNA. This supports rapid growth of T cells and B cells when your body fights infection.
Risk
What if the gene does not work
Variants in the CTPS1 gene can weaken infection-fighting T and B cells, causing an inherited immune condition with recurrent severe viral and bacterial infections. Milder to more severe variants may influence when symptoms begin and how strongly immunity is affected.
Treatment
What does that mean for your treatment
For people with pathogenic variants in the CTPS1 gene, treatment usually centers on immune support and infection control, and hematopoietic stem cell transplantation can be a definitive option. Doctors may use immunoglobulin replacement, antimicrobial prophylaxis, and close monitoring while planning longer term care. No CTPS1-specific drug is currently established.
Conditions associated with CTPS1
Gene function
What if the gene works
When immune cells need to multiply, they depend on a steady supply of small chemical building blocks. The CTPS1 gene helps make one of these, called CTP, which cells use to build RNA, DNA, and cell membranes. This job is especially important during periods of fast cell growth, including normal immune responses.
The CTPS1 gene helps cells make CTP, a key building block used every day inside the body. This supply supports normal cell activity and gives growing cells the material they need.
Cells use CTP to make RNA, which helps turn genetic instructions into working proteins. By supporting this step, the CTPS1 gene helps many cells carry out routine tasks.
CTP also feeds into the pathway that makes DNA building blocks for new cells. This is a core part of the CTPS1 gene’s function in immune cells, especially when T cells and B cells begin to multiply.
Cells also use CTP to make phospholipids (fats that form cell membranes). This helps cells build and refresh their outer covering as they grow and divide.
What is a variant?
A genetic variant is a small difference in the DNA sequence of a gene. These differences are common and are part of normal human diversity, such as variation in appearance, metabolism, or the way the body responds to environmental influences. Many variants do not cause any noticeable effect and simply represent natural genetic variation. In some cases, though, a variant can change the function of a gene more significantly and may contribute to or cause a genetic condition.
Genetic variants
What if the gene does not work
Variants in the CTPS1 gene can lower how much CTPS1 protein a cell makes or leave the protein shortened, unstable, or less active. In CTPS1 gene variants, milder changes may partly reduce enzyme activity, while more severe variants can almost shut it down. This limits a cell's supply of key DNA and RNA building blocks, especially during rapid immune cell growth. Greater functional loss often links to earlier and more pronounced CTPS1 deficiency.
How variants are linked to conditions
Pathogenic variants in both copies of the CTPS1 gene cause CTPS1 deficiency, a rare inherited immune condition also called immunodeficiency 54. People with this diagnosis often have repeated or more severe than expected infections, especially after common viruses such as Epstein-Barr virus. Carrying one CTPS1 variant usually does not cause the condition.
A variant is not necessarily a diagnosis
Genetic variants are common across the general population and are a normal feature of human biology. Most do not directly affect health and simply contribute to natural differences among people. For many genes, having a variant associated with a condition points to a possible link rather than a certain diagnosis, particularly when several genes and environmental influences are part of the picture. In some 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 CTPS1, risk is mainly shaped by inheritance rather than lifestyle. A child’s chance of having CTPS1-related immune problems is higher when both parents carry a harmful change in the CTPS1 gene, especially in families with a known history of the condition.
Inheritance of CTPS1 variants
CTPS1-related disease is inherited in an autosomal recessive pattern. This means a person usually develops the condition only if they inherit two disease-causing variants in the CTPS1 gene, one from each parent. Parents who each carry one variant are typically unaffected carriers, and with each pregnancy they have a 25% chance of having an affected child, a 50% chance of having a child who is a carrier, and a 25% chance of having a child with neither variant. Because the CTPS1 inheritance pattern is recessive, boys and girls are affected equally.
What does my CTPS1 result mean for my family?
For CTPS1, family implications are usually in line with a recessive inherited condition. Parents of someone with a disease-causing CTPS1 result are often healthy carriers, and brothers or sisters may also be affected or be carriers. Other close relatives may carry the same gene change, so the result can matter for family planning and for understanding health risks in the wider family.
Genetic information
Genetic testing
How you find out about variants
To find out whether you carry a CTPS1 gene variant, genetic testing uses a blood sample, saliva, or a cheek swab. Genetic testing for CTPS1 variants reads the DNA code of the CTPS1 gene and looks for changes linked to immune problems related to CTPS1, including whether someone has a harmful variant or is a carrier.
When should I consider getting a genetic test?
Consider CTPS1 genetic testing if a child has severe, repeated infections, especially unusual viral infections, and doctors suspect an inherited immune system condition. Testing can also help when a close relative has a confirmed CTPS1 change or this condition runs in the family.
A genetic result is only one part of your health story
Genetic test results can provide useful insight, but how much they reveal depends on the condition and the type of variant involved. Many factors, including lifestyle, environment, age, and medical history, also shape how the body works over time. For some conditions, especially those influenced by many genes, genetic information provides context rather than certainty and is best understood along with other parts of care. In other situations, a genetic result may offer 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 drug works well for one person, has little effect in another, or causes more side effects in someone else. Differences in how the body breaks down, moves, or responds to a medicine are common, and they can influence both treatment benefit and sensitivity to the drug.
What is Pharmacogenetics?
Pharmacogenetics examines how differences in a person’s genes can affect the way they respond to medicines. By studying links between genes and medications, it helps explain why the same treatment may not work the same way for everyone. With many drugs, genes influence both how the body handles the medicine and how strong its effects are. This information can support more personalized, better informed treatment choices. More detail on this topic is available in the LearnHub.
Drugs influenced by the CTPS1 gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in predicting how medicines will work or what side effects they may cause. If you have questions about a medicine, new side effects, or changes after starting treatment, talk with your doctor or pharmacist.